In pregnancy the placenta becomes a major endocrine organ. Its hormones keep the pregnancy going and adapt the mother's body to feed the growing baby.
hCG
The early placenta makes hCG, which keeps the corpus luteum making progesterone in the first weeks. Pregnancy tests detect hCG in urine or blood, and early on its level roughly doubles every two to three days.
Progesterone and estrogen
From about 10 weeks the placenta takes over making these hormones. Progesterone keeps the uterus calm, and estrogen grows the uterus and the breasts.
Human placental lactogen
This hormone makes the mother's tissues less sensitive to insulin so more glucose reaches the baby. It is the reason gestational diabetes can appear in the second half of pregnancy.
Labor and breastfeeding
Oxytocin makes the uterus contract during labor and after birth, which helps control bleeding. Prolactin makes milk, and oxytocin releases it when the baby suckles.
At the bedside
Do a pregnancy test before X-rays, many medicines and procedures in anyone who could be pregnant. After delivery, a firm uterus and early breastfeeding both rely on oxytocin to limit bleeding.
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Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).