Parturition and Lactation

Parturition and Lactation

The journey from fertilisation to birth is a carefully orchestrated sequence of events. After the embryo implants in the uterus, it develops over approximately nine months into a fully formed foetus. The final stage of this journey — the delivery of the baby — is called parturition, and the mother's body prepares for this event through hormonal changes that also initiate the production of milk for the newborn.

Parturition — The Process of Childbirth

Parturition is the act of giving birth, and it is set off by a complex neuroendocrine mechanism, not a single trigger.

The first signal comes from the foetus and placenta themselves, once they are fully developed. Together they generate signals that produce mild uterine contractions — this initial response is called the foetal ejection reflex. It is this reflex, not a foetal hormone travelling to the mother, that sets the whole process in motion.

The foetal ejection reflex triggers the release of oxytocin from the mother's own pituitary. Oxytocin then acts on the uterine muscle, causing stronger contractions. These stronger contractions in turn stimulate the release of still more oxytocin — a positive feedback loop in which each round of contraction and oxytocin release reinforces the next, so labour intensifies rather than settling down.

This escalating cycle continues until the contractions are strong enough to expel the baby out of the uterus and through the birth canal. The placenta follows shortly afterwards as the afterbirth.

Lactation — The Production of Milk

After the baby is born, the mother's body must provide nourishment. This is achieved through lactation, the process by which the mammary glands produce and release milk.

The hormonal preparation for lactation actually begins during pregnancy. Several hormones work together to develop the mammary glands:

• Estrogens and progestogens (progesterone-like hormones), produced in large amounts by the placenta during pregnancy, stimulate the growth and branching of the milk ducts and the development of the milk-secreting alveoli (the clusters of cells within the mammary lobes).
• Human placental lactogen (hPL) also contributes to the development of the mammary glands during pregnancy.

However, the actual secretion of milk does not occur until after delivery. The high levels of estrogen and progesterone during pregnancy actually inhibit the secretion of milk. Once the placenta is expelled after birth, the levels of these hormones drop sharply. This drop removes the inhibition, allowing the hormone prolactin (secreted by the anterior pituitary) to act on the alveoli and initiate milk secretion. …