American Scientist

Human Chorionic Gonadotropin (hCG)

hCG is produced by the placenta after implantation. It supports the function of the corpus luteum, a temporary structure in the ovaries essential in early pregnancy. It's also the hormone detected by pregnancy tests.

Progesterone

Progesterone helps establish the placenta. It stimulates growth of blood vessels that supply the womb, and it inhibits contraction of the uterus so it grows as the baby does. Progesterone also strengthens pelvic wall muscles for labor.

Estrogen

Estrogen helps the uterus grow, maintains the uterine lining, and helps fetal organs develop. It activates and regulates production of other hormones. With progesterone, estrogen stimulates breast growth and milk duct development.

Prolactin

Prolactin is the main hormone needed to produce breast milk. It contributes to enlargement of the mammary glands and prepares them for milk production. Progesterone inhibits lactation during pregnancy.

Relaxin

Relaxin inhibits uterus contraction to prevent premature birth. It relaxes blood vessels, increasing blood flow to the placenta and kidneys. It relaxes the joints of the pelvis and softens and lengthens the cervix during birth.

Oxytocin

Oxytocin levels rise at the start of labor, stimulating contractions of uterine muscle. It triggers production of prostaglandins, which increase contractions further. If labor doesn't start naturally, oxytocin can be used to induce it.