CHAPTER 4: Breastfeeding, Fertility and Population Growth

Roger Short, Department of Physiology, Monash University, Melbourne, Australia.

Introduction

Humans belong to the Class Mammalia, one of whose distinguishing features is that the newborn young are totally dependent on their mother’s milk for survival. Today, many people have come to regard breastfeeding as an inconvenience, and in one way or another we have been trying to circumvent this biological activity since the dawn of civilization. But breastmilk is our birthright. Breastfeeding has been honed to perfection by millions of years of natural selection, so it is hardly surprising that the premature abandonment of breastfeeding carries heavy penalties for both the mother and her baby. The mother looses the natural contraceptive protection afforded by breastfeeding, and if her children are born too close together their chances of survival are seriously impaired. The mother also looses the protection that breastfeeding can give against the development of ovarian and breast cancer in later life; breast cancer has now become one of the commonest women’s cancers in developed countries. The baby looses both short-term and long-term protection against gastrointestinal and respiratory diseases; diarrhoea is the commonest cause of infant morbidity in developed countries, and mortality in developing ones. Bottle fed babies are also much more likely to develop fatal necrotizing enterocolitis, and to be prone to a whole range of allergies in later life, and may even be less intelligent than their breastfed counterparts, and more likely to develop early age onset diabetes.

Since breastmilk is both the cheapest and the best food ever devised for human infants, why has it taken us so long to appreciate its many benefits? What were the historical factors that led to the abandonment of breastfeeding?

The History of Breastfeeding

Aristotle, writing in 350 B.C., had this to say of breastfeeding:

“Women continue to have milk until their next conception; and then the milk stops coming and goes dry, alike in the human species and in the quadrupedal vivipara. So long as there is a flow of milk the menstrual discharges do not take place as a general rule, though the discharge has been known to occur during the period of suckling.”⁽¹⁾

Thus Aristotle had a clear understanding of the phenomenon of lactational amenorrhoea, and he also appreciated that menstruation could return even though the woman was continuing to breastfeed. He even commented on the contraceptive effect of lactational amenorrhoea:

“While women are suckling children menstruation does not occur according to nature, nor do they conceive; if they do conceive, the milk dries up”.⁽²⁾

The fact that if a woman became pregnant whilst lactating, her milk secretion would cease, is an important point to which we will return later.

Since the dawn of civilization, we have been interfering with the normal pattern of breastfeeding^(3,4). Even the Pharaohs used wet nurses for rearing their children. Both Moses and Mahomed owed their lives to wet nurses after they were rescued from the bullrushes. The earliest known feeding bottles for administering animal milks to human infants date from about 4000 B.C., and large numbers of these feeding vessels of different designs were found in children’s graves all over Greece and Italy; perhaps they had unknowingly been the cause of the infant’s death in many instances. The suckling of human infants by animals was also a common theme in mythology - Romulus and Remus, the twin founders of Rome in the 8th Century B.C., were suckled by a wolf, and Zeus was suckled by a goat.

Table 1 summarizes some of the evidence⁽³⁾ about the ages at which babies were weaned from the breast in the ancient world. It is interesting that although most Egyptians, Babylonians and Hebrews traditionally breastfed their children for about 3 years, the wealthier Greeks and Romans hired slaves as wet-nurses to take over this duty. In Plato’s Republic, he advocates the rearing of all children in creches by wet nurses, “while taking every precaution that no mother shall know her own child”. The bonding effect of breastfeeding was evidenced by the lifelong attachments that were often formed between children and their wet nurses, sometimes at the expense of the child’s relationship with its natural mother⁽⁴⁾; this was the reason why many Roman philosophers and moralists such as Pliny, Plutarch and Tacitus spoke out so strongly against wet nursing.

Table 1: Age of Weaning in the Ancient World

Culture	Age (months)
Pharaonic Egypt	36
Babylonian	36
Hebrew	36
Greek	6 wet nursing contract
Roman	6-36 16 wet nursing contract
Byzantine	24
Islamic	24

In the Middle Ages, medical writers began to recommend earlier and earlier ages at weaning (see Table 2), and there was much interest in the development of paps, panadas and gruels as early weaning foods⁽³⁾. Gradually, the administration of these foods, referred to as “dry nursing”, came to be regarded as an alternative to wet nursing for the artificial rearing of infants, although the mortality rates associated with this practice were staggeringly high. Nowhere was this more evident that in the Foundling Hospitals, established in most of the big cities of Europe to care for illegitimate, abandoned or orphaned children. Table 3 summarizes the figures for just 3 of these institutions. The Dublin Foundling Hospital functioned more like a slaughterhouse. Many Foundling Hospitals were opened in Italy between the 11th and 15th centuries, supported by the Church, and it is particularly fitting that the Florence Foundling Hospital, the Spedale degli Innocenti, should have given its name to the 1990 U.N.-sponsored Innocenti Declaration on the Protection, Promotion and Support of Breastfeeding⁽⁵⁾. With our new-found knowledge about the manifold benefits of breastfeeding, perhaps we can begin to redress the centuries of abuse of this practice.

Table 2: Ages of Weaning Recommended by Early Medical Writers

Date	Weaning age (months)
1540 - 1584 (4 authors)	24 - 36
1612 - 1699 (7 authors)	12 - 24
1729 - 1748 (5 authors)	8 - 24
1753 - 1799 (13 authors)	6 - 12

Table 3: Mortality Rates in European Foundling Hospitals in the 18th Century

Hospital	Dates	No. of deaths and % of mortality		Method of Feeding
London	1741-59	7,833	56%	wet nursing
Paris	1773-77	25,476	80%	wet nursing
Dublin	1775-96	10,227	99.6%	dry nursing

It was an Eighteenth Century English physician, Dr. W. Cadogan, often regarded as the Founding Father of Paediatrics, who probably determined many of our present-day attitudes to breastfeeding. He was Physician to London’s Foundling Hospital, and achieved fame by lowering the rates of infant mortality in that institution to around 56% by bringing in wet nurses from the surrounding countryside to breastfeed the inmates, in contrast to the dry nursing with paps and gruels that effectively killed 99.6% of the inmates of Dublin’s infamous Foundling Hospital. Cadogan published a pamphlet entitled “An Essay upon Nursing and the Management of Children from their Birth to Three Years of Age” in 1748⁽⁶⁾, and this 43 page treatise was translated into French and reprinted many times in England, France and America throughout the eighteenth century. It must have had an enormous influence on the attitudes of nurses and doctors to breastfeeding; many of Cadogan’s prejudices have persisted up until the present day. Some of Cadogan’s statements therefore bear close attention in the light of what we now know about human lactational physiology.

A large number of Cadogan’s observations were perfectly correct, and remarkably perceptive. For example, when speaking about when it first becomes necessary to supplement the diet of the breastfed baby, he says

“If I could prevail, no Child should ever be crammed with any unnatural mixture, till the Provision of Nature was ready for it; nor afterwards fed with any ungenial diet whatever, at least for the first three months: for it is not well able to digest and assimilate other aliments sooner.”

Most significantly, he goes on to say

“I have seen very healthy fine Children, that never eat or drank any thing whatever but the Mother’s milk for the first ten or twelve months. Nature seems to direct this, by giving them no teeth ‘till about that time.”

The use of tooth eruption to indicate the time at which supplements should first be introduced into the diet of the breastfed baby makes sound physiological sense, and it is surely part of Nature’s design. For our hunter-gatherer ancestors, whose dental eruption patterns we have inherited, there were no special weaning foods available such as animal milks or cereal flour; the infant had to be supplemented with items from the adult’s diet, which would have required that the infant had teeth for biting and chewing. Table 4 summarizes the development of a child’s primary dentition. Maybe we should revert to tooth eruption as an excellent signpost for the mother about when to start supplementing the baby’s diet.

Table 4: Development of Human Primary Dentition

Tooth	Age at Eruption (months)	Age at Root Completion (years)
Central Incisors	6	1.5
Lateral Incisors	8	1.5 - 2
Canines	17	3.25
First Molars	13	2.5
Second Molars	22	3

But if Cadogan gave good advice about the timing of first supplement introduction, he gave manifestly bad advice about the frequency of breastfeeding:

“By night I would not have them fed or suckled at all, that they might at least be hungry in a morning. It is this night-feeding that makes them so over-fat and bloated. If they be not used to it at first, and, perhaps, awaked on purpose, they will never seek it; and if they are not disturbed from the birth, in a week’s time they will get into a habit of sleeping all or most part of the night very quietly; awakening possibly once or twice for a few minutes when they are wet, and ought to be changed. Their meals, and, in my opinion, their sucking too, ought to be at stated times, and the same every day; that the stomach may have intervals to digest, and the appetite return.”

This last sentence seems to have been the origin of those rigid feeding schedules, so well suited to a hospital’s routine, so ill-suited to the needs of the baby and its mother. In traditional hunter-gatherer societies, where the baby sleeps beside its mother, on the ground, it can feed at will throughout the night without even wakening its mother. Frequent feeding, both by night and by day, is the best way of increasing the mother’s milk supply, whilst at the same time ensuring that breastfeeding has its greatest contraceptive impact because of the frequent nipple stimulation. Night-time feeding became increasingly impractical and unpopular as we began to sleep on raised beds. The mother feared that the baby might fall out, or might be smothered by the blankets, so the baby was put into a separate cot. Then it began to cry when it wanted a feed, waking both husband and wife; so the cot was banished to another room, where the baby’s cries would be muted, at least to the husband’s ears. Thus began the irrevocable separation of the infant from its mother, subsequently reinforced by the advent of nannies, and more modern paraphernalia such as creches, perambulators, playpens and “dummies” or “comforters”.

Cadogan was at a loss to explain why breastfeeding was becoming so unpopular:

“Because most Mothers, of any condition, either cannot, or will not undertake the troublesome task of suckling their own Children; which is troublesome only for want of proper method; were it rightly managed, there would be much pleasure in it, to every Woman that can prevail upon herself to give up a little of the beauty of her breast to feed her offspring; though this is a mistaken notion, for the breasts are not spoiled by giving suck, but by growing fat.”

In today’s breast-conscious Western society, some women, and probably many men, secretly resent breastfeeding because of a fear, expressed in a recent letter by a male correspondent to the Lancet⁽⁷⁾, that it will inevitably result in drooping, saggy breasts in later life. But I have yet to meet a gynaecologist who could diagnose with conviction whether or not a woman had ever breastfed, based on a clinical examination of her breasts. Maybe we need some “Before and After” photographs of the breasts of breastfeeding and bottlefeeding women taken during youth and again in middle age to drive the point home to men and women alike. This might be more effective in changing Western attitudes than publicity about the manifold health benefits of breastfeeding. And since the Western, developed world is so often the trendsetter for change in the developing world, changing Western attitudes should be a most important objective.

Unfortunately, Cadogan’s idea about the optimal frequency of the baby’s breastfeeds was hopelessly wide of the mark:

“Four times in four and twenty hours will be often enough to give it suck”.

This would seem to be the origin of the 4-hourly feeds that some nurses and doctors have made almost a statutory requirement. But we now know that the breast is ingeniously designed to ensure that milk supply meets milk demand, and that the frequency of feeding is best determined by the baby. The mammary alveoli secrete an inhibitory peptide into the milk, and if the breast is not emptied frequently, the peptide will prevent further milk synthesis⁽⁸⁾. Normal suckling frequencies, as observed in!Kung hunter-gatherers, are about 4 times an hour⁽⁹⁾ - sixteen times the frequency advocated by Cadogan! Since the human breast, unlike the udder of the cow, does not contain a large storage area or milk cistern for the accumulation of all the milk secreted between feeds, its very anatomy tells us that it was designed for frequent feeding. The composition of the milk reinforces this. Mammals that feed their young relatively infrequently, such as once a day or less as in rabbits, hares, tree shrews, seals etc., have milk with a high protein and fat content; in contrast, humans, with their incredibly slowly growing but frequently fed infants have a very low protein and a low fat content milk that is extremely rich in the carbohydrate lactose⁽¹⁰⁾.

Adoption of Cadogan’s 4 feeds a day routine would make early introduction of supplements essential, since the baby would soon not be getting enough milk to sustain its needs. Four feeds a day is also not enough to provide long-term contraceptive protection; the breastfeeding mother on such a regime would soon become pregnant again. Reducing the suckling frequency in this way would therefore put at hazard not only the baby at the breast, which would be starved of appropriate nutrients and rendered susceptible to a range of diseases when supplements were introduced, but it would also endanger the life of the subsequent child, which would have been conceived prematurely. A new conception following too hard on the heels of a preceding birth leaves the mother with depleted energy stores, and so the growth rate of the fetus is reduced, resulting in the birth of a small-for-dates baby with impaired chances of survival⁽¹¹⁾ (see Fig. 1). And as Aristotle had correctly observed, a new pregnancy would soon dry up the mother’s remaining milk supply, so that the older child might develop Kwashiorkor - originally a West African word, with the prophetic meaning “The evil eye of the child in the womb upon the child already born”, used to describe the often fatal signs of protein and calorie malnutrition in infants.

Figure 1. Annual mortality rates per 1,000 children aged 1-4 in 24 developing countries, depending on whether the child was born after a short (<2 years) or a long (2-6 year) preceding birth interval.

Source: Adapted from Chart 4 in Maine, O. and McNamara, R. (1985). Birth Spacing and Child Survival, Center for Population and Family Health, Columbia University.

Cadogan made only one brief mention of the contraceptive effects of breastfeeding, and this was in relation to criteria for the selection of appropriate wet nurses; he recommended using only those who have given birth less than 2-3 months previously, believing, incorrectly, that the milk was of little nutritional value if a woman lactated beyond a year, especially if her periods (catamenia) had returned:

“Nature intending a Child should suck about a twelvemonth, the milk seldom continues good much longer. About that time, Women in general, though they give suck, are apt to breed again; some, indeed, that are very sanguine, will breed sooner; these, notwithstanding their milk, are apt to be troubled with the catamenia, which disturb it greatly; and therefore are not so proper to be made Nurses of.”

In summary therefore, although Cadogan was a strong advocate of breastfeeding, it is ironical that some of his recommendations undermined many of its advantages for the mother and her baby.

The aristocracy, who were the trend-setters in European society in times past, had been quick to exploit the fact that the contraceptive effect of breastfeeding could be circumvented by the use of wet nurses, thereby making it possible for their wives to produce a child a year, even if many of the infants failed to survive (see Fig. 2). Large families were an advantage to royalty and the nobility, since by arranging the appropriate marriages of sons and daughters, the family could acquire wealth, power and influence.

Figure 2.

A seventeenth-century engraving of Sir Thomas and Lady Remmington of Lund, Yorkshire, with their 20 children five of whom evidently died in childhood. The skull in the bottom left foreground presumably indicates an additional late fetal death or stillbirth. Lady Remmington could never have produced so many children if she had breastfed them; she must have practiced the custom of the day and sent them out to be wet nursed.

The short-sightedness of using wet nurses, or artificial feeding with infant gruels, paps and panadas, was well known. Newcome⁽¹²⁾, in a late 17th Century pamphlet entitled “The Compleat Mother or, An earnest persuasive to all mothers (especially those of rank and quality) to nurse their own children”, had this to say on the subject:

“So vain is that popular pretence that nursing is an impediment to fruitfulness, and to be declin’d by great persons for the better securing of succession, by a numerous posterity: for if those bear faster who dry up their breasts, they that nurse their children commonly bear longer, and bring up more to maturity.”

Almost a century later, Mary Wollstonecraft⁽¹³⁾, the pioneer of the feminist movement, made a plea for breastfeeding in her book “Vindication of the rights of woman”:

“Nature has so wisely ordered things that did women suckle their children, they would preserve their own health, and there would be such an interval between the birth of each child, that we should seldom see a houseful of babies.”

But these admonitions went largely unheeded in the male-dominated societies of those times. Jean-Jacques Rousseau, the renowned French philosopher, and exponent of the idea that all goodness resided in primitive man, the Noble Savage, only to be corrupted by civilization, had a great influence on how middle-and upper-class parents reared their children following the publication of his book Emile in 1762. Rousseau was greatly admired by Mary Wollstonecraft, but he set a pretty bad example by having all his own five children sent to a foundling hospital at birth, never to be seen by him again! In his later years, he made fruitless attempts to trace their whereabouts.

This reliance of the nobility on wet nurses may have had unforseen consequences for family structure, surely a rich field of exploration for some future social historian. Remembering the Roman philosophers’ concern for the powerful bonding of the infant to its wet nurse rather than to its natural mother, it is difficult to imagine a more traumatic succession of events that those that would take place during the early years of life of a young aristocrat. Despatched to a wet nurse, often many miles away in the countryside, within a few days of birth⁽⁴⁾, the mother might not see it again for a couple of years. The wet nurse, in the early months of her lactation, would be some poor country girl, probably unmarried, who had recently lost her own baby, or been forced to give it away, or even worse. She would naturally transfer all her maternal affection to this surrogate child, and could earn a reasonable living by caring for it. Imagine her grief when, at the end of this time, “her” child was taken away from her, never to be seen again. But imagine the greater grief of the child, forcibly removed from its adoring wet nurse, to be returned to a mother it did not recognize, a mother who herself would have had another one or two children in the interim, and who would have neither the time nor the inclination to give the child her undivided love and attention. What chance was there of ever re-establishing those broken mother-infant bonds? Little wonder that in such large, cold, impersonal extended families, children were often little more than chattels, to be bought and sold in marriage. Could it even be that the Age of Exploration was ushered in by such behavioural upheavals? Forsaking home and family for years on end to travel the world might have been a welcome escape from a loveless home environment.

There is even some evidence to suggest that wet nursing was a practice that was exported to the slave colonies of the Caribbean. Since slaves were worth money, the more babies a slave woman could produce the better. Thus it apparently became a practice to employ elderly wet nurses on the slave farms to rear several children at a time, so that the mothers could become pregnant again as soon as possible. When we look at breastfeeding practices in the independent Caribbean nations today, it seems significant that those with the lowest acceptance of breastfeeding are also those that were longest under the colonial yoke⁽¹¹⁾.

We can begin to get some idea of the consequences of the inappropriate artificial feeding of infants from Hugh Smith’s “Letters to Married Women on Nursing and the Management of Children”, published in 1772⁽¹⁴⁾. He tabulated the annual number of births registered in the City of London for each of the 10 years from 1762 to 1771, and related it to the annual number of burials of children. The averages worked out at 16,283 births per year, with 7,987 burials of children under the age of 2, and 10,145 burials under the age of 5. Thus almost half the children born in the City were dead within 2 years; he was in no doubt as to the cause of this staggering mortality:

“It is well known, that the thrush and watery gripes generally terminate their existence in the early months ..... The thrush and watery gripes are, in the author’s opinion, artificial diseases, and both of them totally occasioned by improper food, such as all kinds of pap, whether made from flour, bread, or biscuit; they all cause too much fermentation in an infant’s stomach, and irritate their tender bowels beyond what Nature can support.... Let me then intreat those who are desirous of rearing their children, not to rob them of their natural breast. Would they wish them to be healthy and beautiful, let such mothers give suck: for even wet-nurses, we shall find, are very little to be depended upon”.

How right he was.

The Uniqueness of Human Milk

The enormous infant mortality rate consequent upon the artificial feeding of babies with wholly inappropriate foods was a challenge to the nutritionists of the day. Some of the Foundling Hospitals, appreciating the benefits of wet nursing as opposed to dry nursing, started to experiment with animal milks in place of human milk. Some French hospitals even kept their own lactating goats and donkeys, and the babies were wheeled beneath them at feeding time, so that they could suck directly from the animal’s teats⁽⁴⁾. But no milk from any domesticated animal comes close to the high lactose, low protein content of human milk, and so it was necessary to try and re-formulate the animal milk, to “humanize” it in order to make it more appropriate for the baby’s needs. Thus was born the powdered milk industry, which is still trying, in vain, to turn cow’s milk products into something that could pass for human milk. But even if we were able to emulate the chemical composition of human milk, it would be impossible to devise an animal milk with the unique biological properties of human milk.

Recent research has revealed the great subtlety of the enteromammary circulation⁽¹⁵⁾ (see Fig. 3). The mother stores up an immunological memory of all the pathogens ingested during her life, a memory that is retained in specific b cells in the Peyer’s Patches, large aggregates of lymphoid tissue lying in the mesentery of the small intestine. During lactation, probably under the influence of the hormone prolactin, these b cells migrate via the blood circulation and come to rest in the mammary gland (and also the salivary glands). There, they become transformed into plasma cells, which secrete immunoglobulin A into the breast milk in enormous quantities - up to ½ gm a day in the early months of lactation. This immunoglobulin is scarcely absorbed by the baby, but remains in the gut lumen, where it can prevent organisms attaching to the gut wall and setting up an inflammation. The mother is constantly biopsying her environment through her mouth, and should she swallow a pathogen to which her b cells have previously been sensitized, she will immediately start excreting large quantities of the appropriate neutralizing immunoglobulin in her milk.

Figure 3. The Entero-Mammary Circulation

The ingestion of a pathogen by the mother results in the activation of previously sensitized B lymphocytes in the Peyer’s patches of her small intestine. These migrate in the blood stream to the breast, where they develop into plasma cells secrete into the milk a specific immunoglobulin A directed against the pathogen. This antibody is ingested by the baby, and is neither absorbed nor destroyed, but remains in the gut lumen, where it protects against gastroenteritis.

There is even one further twist to this remarkable story; many animals including the higher primates will lick the faeces of their infants during suckling, thereby biopsying their excreta for signs of pathogens. Although humans do not normally indulge in coprophagia because of our revulsion at the smell of our own faeces, it seems significant that women universally find the smell of the faeces of exclusively breastfed babies not the least unpleasant, so there is no need to wash your hands if the baby defaecates on you. Thus even in humans, there is ample opportunity for the mother, albeit unknowingly, to swallow any pathogen that here baby may be excreting, and subsequently passively immunize the baby against the organism with a specific 1gA excreted in her breast milk.

Thus human breast milk is a living, dynamic secretion, changing in composition in response to the baby’s needs. There is no way that any manufacturing process could ever tailor-make a synthetic milk to meet the different immunological demands of each and every infant.

The uniqueness of breast milk is not confined solely to its immunological composition. Recent research has shown that human breast milk also contains a high concentration of epidermal growth factor⁽¹⁶⁾, in contrast to cow’s milk which contains relatively little. This may have a vital role to play in the post-natal maturation of the infant’s gastrointestinal tract. The human baby is born with a relatively porous gut, and if foreign proteins, such as cow’s milk, are introduced into the baby’s diet in the first months of life before gut closure has occurred, they can be absorbed unchanged into its circulation, where they may provoke an immune response. This precocious sensitization of the baby to foreign proteins may be the reason why bottle-fed babies are so much more prone to allergies in later life. The role of epidermal growth factor in promoting post-natal development of the gut may also explain why it is that the protective effects of early breastfeeding against gastrointestinal infections far outlast the duration of breastfeeding. A recent study in Dundee, Scotland, showed that babies that had been exclusively breastfed for a full 3 months were protected from gastroenteritis for at least a year⁽¹⁷⁾.

The mechanism by which breastfeeding exerts its contraceptive effect

We now have a good understanding of the mechanisms by which breastfeeding exerts its contraceptive effect⁽¹¹⁾. Afferent nerve impulses generated by the sucking activity of the baby on the nipple pass up the spinal cord to reach the hypothalamus at the base of the brain. In response to these neural inputs, the brain opiate b endorphin is released in the hypothalamic area, where it appears to have two important effects. Firstly, it decreases the hypothalamic secretion of the gonadotrophin releasing hormone, GnRH, which in turn regulates the secretion of the gonadotrophins follicle stimulating hormone (FSH) and luteinizing hormone (LH) by the anterior pituitary gland. These gonadotrophins are normally responsible for ovarian follicular development and ovulation; women in lactational amenorrhoea have an impaired pulsatile secretion of LH from the anterior pituitary, and this is thought to be the principal mechanism suppressing ovarian follicular development and ovulation⁽¹⁸⁾. Secondly, b endorphin also suppressed the hypothalamic secretion of dopamine. Dopamine is the prolactin-inhibitory hormone; it normally holds prolactin secretion by the anterior pituitary gland in check. During the early months of lactation, when the suckling frequency is highest, b endorphin suppresses dopamine secretion and prolactin secretion is therefore elevated. Prolactin appears to be an important metabolic hormone, and is essential for the long-term maintenance of lactation.

Suckling also causes the release of the hormone oxytocin from the posterior pituitary gland, and this acts on the myoepithelial cells of the mammary alveoli, causing them to contract and squeeze the recently synthesized milk out into the milk ducts that are connected to the nipple; the breastfeeding mother knows this as the milk ejection reflex. Thus in response to suckling oxytocin serves today’s meal, whilst prolactin prepares the menu for tomorrow, but neither of these hormones is now thought to play any role in the contraceptive effect of breastfeeding.

From this account, it can readily be appreciated that coupled with a relatively high rate of infant and childhood mortality, this effectively held rates of population growth in check. Breastfeeding was Nature’s contraceptive. But those days are gone, never to return; few societies would be prepared to breastfeed their infants so intensively. The challenge we face today is to retain as many of the advantages of breastfeeding as possible, and to augment its contraceptive effects by the frequent nipple stimulation is important not only for ensuring an adequate production of milk, but also for suppressing ovarian activity.

How can we capitalize on the natural contraceptive effects of breastfeeding, and integrate it into family planning programmes in order to achieve optimal birth spacing?

In our hunter-gatherer ancestors, who had no knowledge of or access to other forms of contraception, frequent and prolonged breastfeeding by day and by night resulted in children being born about 4 years apart, and appropriate introduction of modern forms of contraception. Even to this day, breastfeeding still prevents more births in most developing countries than all modern forms of contraception⁽¹¹⁾, but breastfeeding alone will no longer keep population growth in check, especially since we have now lowered infant and childhood mortality rates to more acceptable levels.

The ultimate objective must be to achieve an interval between successive births of at least 2 years, since this will maximize infant survival (see Fig. 4). This means that the mother must be guaranteed at least 15 months of postpartum contraception. But how long should she breastfeed for, and for how long will breastfeeding protect her against pregnancy?

Figure 4.

An aboriginal woman with her six children, including one pair of twins. At the time this photograph was taken the mother was 20.6 years old, the eldest child was 7 and the twins 6 months old. All the children grew normally whilst exclusively breastfed, yet all demonstrated growth failure following the introduction of supplementary feeding, which also obviously eroded the contraceptive effect of breastfeeding and resulted in such spectacular fertility. Source: Cox (1978)²⁵.

The Innocenti Declaration states that all women should be enabled to practice exclusive breastfeeding for 4-6 months, and that thereafter, children should continue to be breastfed for up to two years of age or beyond, whilst at the same time receiving appropriate and adequate complementary foods. The Declaration makes no recommendation about the timing or frequency of feeds, but if the baby is fed on demand, and not according to some prearranged schedule, it will regulate its suckling frequency and hence the supply of milk according to its needs. Under such circumstances, most mothers will experience at least 6 months of lactational amenorrhoea. In a population of 101 well-nourished Australian women, 97% of whom breastfed exclusively for at least 4-6 months, and some for as long as 8-10 months, the mean duration of lactational amenorrhoea was 9.5 months⁽²⁰⁾. During the early months of lactation, the first post-partum menstruation is likely to precede the first post-partum ovulation, so initially lactational amenorrhoea affords excellent contraceptive protection. The Bellagio Consensus Conference on breastfeeding as a family planning method established that a mother who is fully or nearly fully breastfeeding her infant and who remains amenorrhoeic will have more than 98% protection from pregnancy in the first 6 months postpartum⁽²¹⁾. In our large Australian cohort, only 1.7% would have become pregnant during the first 6 months of amenorrhoea and only 7% during the first 12 months or amenorrhoea, regardless of whether or not they had begun to introduce supplements into the baby’s diet⁽²²⁾ (see Fig. 5). But when lactational amenorrhoea extends beyond 12 months, ovulation is increasingly likely to precede the first postpartum menstruation, so the woman can no longer rely on the first menstruation as a preliminary sign that her fertility is about to return.

Figure 5.

The cumulative probability of becoming pregnant during breastfeeding, based on a prospective study of 101 well-nourished Australian women who breastfed throughout the duration of the study, and in whom the time of first postpartum ovulation and menstruation was carefully recorded. The data show that lactational amenorrhoea provides excellent contraception for the first 6 months postpartum. - - - - = non-lactating women of normal fertility having unprotected intercourse; = our breastfeeding women having unprotected intercourse throughout 24 mo of lactation; = our breastfeeding women having unprotected intercourse only during lactational amenorrhoea, and adopting effective contraceptive measures at resumption of menstruation. Percentage of women in lactational amenorrhoea by month post partum () is also shown. Adapted from Short et al., ref. 22.

The programmatic implications are therefore relatively straightforward. Women should be encouraged to breastfeed their babies exclusively for at least 4-6 months, and can rely on lactational amenorrhoea during these first 6 months to give excellent contraceptive protection. Once their periods resume, they must adopt alternative forms of contraception if they do not wish to become pregnant. If the contraceptive failure rate is to be kept below 5%, it would be advisable to take alternative contraceptive precautions after 6 months, even though lactational amenorrhoea still persists.

If hormonal methods of contraception are to be used by breastfeeding mothers, gestagen-only pills, injections or implants are the methods of choice, since they have no adverse effects on milk composition or yield. Oestrogen-containing contraceptives, such as the combined oestrogen/gestagen pill, can cause a significant depression of milk yield. In cultures where HIV infection is prevalent and there are taboos on intercourse during the postpartum period which might encourage the husbands to cohabit with other women during that time, condoms are the contraceptive of choice, especially since the baby is most likely to become infected with HIV via the breastmilk if the mother herself first becomes infected during lactation.

The Effects of Nutrition on Lactation

The maternal plane of nutrition has to be severely depressed before milk yield is adversely affected; farmers are well used to the concept that a lactating dairy cow will “milk off her back”, first depleting her own energy reserves in order to keep up her milk supply. And since the contraceptive effect of breastfeeding depends on a neuroendocrine reflex, not a metabolic one, it is not surprising that within limits, the duration of lactational amenorrhoea is unrelated to the mother’s nutritional status⁽²⁰⁾. But in extreme cases, when the mother is so severely malnourished that her milk supply starts to decline, the suckling frequency of the infant will increase in an attempt to make up the deficit, and this in turn can increase the duration of lactational amenorrhoea. These considerations also suggest why it is that supplementing the diet of the breastfeeding mother has relatively little effect on her milk yield²³.

Since many mothers in developing countries are malnourished, we need to determine how best to supplement their diet, and that of their infants, without repeating the mistakes of the past. The Western world, with its highly developed agriculture, can produce enormous surpluses of cow’s milk. But whilst cow’s milk is an excellent form of nutrition for adults, it is disastrous for young infants. It can be particularly inappropriate for famine relief, since there may be no clean water available for reconstituting the milk, and if mothers are encouraged to forsake breastfeeding for bottlefeeding, many will soon become pregnant again, and many of their infants will die of diarrhoea.

One way of ensuring that the milk is not fed to infants is to distribute it not as a powder which has to be reconstituted as a liquid, but as a high protein, high energy biscuit. Several milk biscuits have been developed²⁴, and these should be ideal for supplementing the diet of mothers during pregnancy and lactation, and as a supplement to the diet of the breastfed infant. Since the infant requires teeth to chew the biscuit, this will ensure that the supplement is not given to it prematurely, and hence the biscuit will not interfere with the 4-6 months of exclusive breastfeeding that is so important for infant health. Because the biscuits will encourage the mother to continue breastfeeding, they will also serve as contraceptives. Since the biscuits are relatively sterile, and do not have to be mixed with contaminated water, or fed through contaminated bottles and teats, they should reduce the chances of the infants picking up infections at the time of supplement introduction. Biscuits are also simpler to package than milk powder - they can be kept in paper wrappings rather than in tins - and they have a long shelf life.

The export of milk biscuits by donor countries would support their own dairy industries. And instead of the UN agencies and health authorities having to berate the multinational infant formula companies for the inappropriate advertising, distribution and sale of breastmilk substitutes in developing countries, the donor nations, the UN agencies, the multinational companies and the recipient nations could make common cause to promote the product. Everybody would have something to gain in this system, and each could be seen to be doing well by doing good.

Conclusions

Since the dawn of civilization, we have been interfering with breastfeeding. The rearing of infants on artificial foods has been the largest uncontrolled clinical experiment ever undertaken, and it is still going on, despite the disastrous consequences. It has brought untold suffering, disease and death to countless millions of babies. The erosion of breastfeeding’s natural contraceptive effect has been a major factor in bringing about the recent explosive growth of the human population. With human numbers now increasing by a quarter of a million people a day, this is surely the transcending problem of our time.

There is no cheaper or more effective way of improving maternal and infant health and lowering fertility, than the promotion of breastfeedings. As Hugh Smith said, over 200 years ago, “Let me intreat those who are desirous of rearing their children, not to rob them of their natural breast”. When will we ever learn?

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