Fetal ripening.
Babies do not manifest complications of organ immaturity such as hyaline membrane disease when they are born from a hormone milieu dominated by estrogen as shown by vaginal cytology. Those who are delivered from a progesterone-influenced environment are at risk for developing the problems of immaturity. A fetus probably 'ripens' in late pregnancy under the control of estrogen.
D004967:Estrogens / Q000502:physiology*; D005260:Female; D005325:Fetal Organ Maturity; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D011263:Pregnancy Trimester, Third; D011374:Progesterone / Q000502:physiology*
D004967:Estrogens; D011374:Progesterone