Theses medicae de divina et admiranda hominis in utero formatione

LXVIII.
Twins arise when there is such an abundance of matter that it suffices for generating two or more fetuses: or even the matter itself is split and divided, especially if it is received in different ends of the uterus.

LXIX.
After the fetus has attained its maturity in the mother's womb, it desires fuller nourishment, and it cannot be contained within any longer due to the narrowness of the place and its own weight. Therefore, it inverts its head, which had been directed upwards for nearly eight months, and as birth is imminent, it kicks with its hands and feet and breaks the membranes: once these are broken, the urine flows out, which is a sign that birth is imminent.

LXX.
From this flow of urine, two advantages arise. First, the orifice of the uterus and the female parts are made slippery and looser, so that the exit of the infant is easier. Second, more space is made in the uterus, so that the fetus can more easily turn itself onto its head.

LXXI.
Man comes into the light with more difficulty than all other animals, because of the size and roundness of the head. For other animals are endowed with a smaller head, which tapers to a point.

LXXII.
To the birth, there also concur: both the expulsive faculty of the uterus itself, which expels the fetus with great effort; and the woman herself, who, by holding her breath and contracting and tensing the muscles of the abdomen, strives to push out the fetus vigorously.

LXXIII.
Miscarriage, which is nothing other than the immature and violent excretion of the fetus, can happen for various reasons: as when the uterus is oppressed by the weight of humors that it contains beyond its strength; or when it is disturbed by humor poured into it, the membranes in which it was contained having been ruptured; or because it is irritated by a putrid and sanious fetus, or vexed for some other cause situated outside it, such as a vehement fever, a flux of the bowels, an immoderate evacuation of blood, jumping, shouting, anger, sadness, fear, a more sparing diet, or by amblōtikois abortifacient medicines, it is forced to corrupt and emit the fetus before the legitimate time.