Astrology was very much popular in the Middle Ages and each astrological sign was correlated with a part of the human anatomy. This interesting tidbit appears on page 111 in Nancy G. Siraisi's "Medieval and Early Renaissance Medicine":
"In addition the the general influence of the heavenly bodies the horoscope at conception or birth was also considered to signal or predispose the physical and mental constitution of each individual down to the most minute detail; Pietro d'Abano held the stars responsible for his own dislike of, or possibly allergy to, milk. Horoscopic astrology thus had a place in reproductive theory as well as medical practice, in which its main uses were in selecting regimen and treatment. It could also provide a form of reproductive planning: the Emperor Frederick II delayed sexual intercourse with his bride until his astrologers told him the propitious moment for the generation of a male had arrived; immediately after the marriage had been consummated according to the astrologers' recommendations, the emperor confidently informed the empress that she was now pregnant with a son. According to the chronicler Matthew Paris, who reported the story, the astrologers had given the right advice, and nine months later the empress duly gave birth to a boy."