Pregnancy
- Pregnancy increases estrogen and progesterone, which maintain the endometrium and suppress new ovarian follicle development.
- Placental hCG rescues the corpus luteum soon after fertilization.
- During the first trimester, hCG-driven corpus-luteum secretion supplies estradiol and progesterone.
- hCG peaks near gestational week 9 and then declines.
- During the second and third trimesters, the placenta becomes the main progesterone producer.
- Placental estrogen is made from fetal adrenal dehydroepiandrosterone sulfate and modified by the fetal liver and placenta.
- Estriol is the major placental estrogen.
- Human placental lactogen is produced throughout pregnancy and has growth-hormone-like and prolactin-like actions.
- hCG maintains the corpus luteum early in pregnancy, while later placental estrogen synthesis depends on fetal adrenal, fetal liver, and placental processing steps.
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