Parturition and lactation

Parturition, the delivery of the foetus, is brought about by strong uterine contractions when pregnancy ends. A complex neuroendocrine mechanism controls it.

The signals that start it come from the placenta and the fully developed foetus, and they produce mild uterine contractions called the foetal ejection reflex.

This reflex triggers the release of oxytocin from the mother's pituitary. Oxytocin acts on the uterine muscle to cause stronger contractions, which in turn prompt still more oxytocin release, a positive feedback loop.

The loop continues, with contractions growing stronger, until the baby is pushed out through the birth canal. The placenta is expelled from the uterus soon after birth.

The mammary glands differentiate during pregnancy and begin producing milk towards its end; making milk is called lactation and it helps the mother feed her newborn.

The milk of the first few days is colostrum. It contains several antibodies that are essential for building resistance in the newborn, which is why breastfeeding in this early period is recommended by doctors.