Step by Step
1
First trimester — the corpus luteum is in charge
hCG, produced by the trophoblast, maintains the corpus luteum, which in turn produces progesterone and estrogen — maintaining the endometrium and suppressing new menstrual cycles. hCG peaks around week 8-10, and its levels correlate with morning sickness severity.
2
The luteoplacental shift (week 10-12)
Around week 10-12, the placenta itself takes over progesterone and estrogen production — at this point, the corpus luteum is no longer needed and can degenerate without ending the pregnancy.
3
Second and third trimester — the placenta takes full control
The placenta produces estrogen (using fetal adrenal DHEA, converted via placental aromatase) and progesterone, with levels of both rising throughout the remainder of pregnancy. Progesterone specifically suppresses myometrial contractions — essential for preventing premature labor.
4
Other pregnancy hormones
Relaxin (from the corpus luteum and placenta) loosens pelvic ligaments and softens the cervix, preparing the body for delivery. Human placental lactogen (hPL), from the placenta, promotes fetal growth, prepares the mammary glands, and causes insulin resistance (a diabetogenic effect).
Applied Walkthrough
1
In early pregnancy, hCG from the developing trophoblast keeps the corpus luteum alive, which continues producing progesterone and estrogen to maintain the endometrium and prevent the return of menstrual cycles.
2
Around week 10-12, a critical transition (the luteoplacental shift) occurs: the placenta itself becomes capable of producing sufficient progesterone and estrogen on its own, meaning the corpus luteum is no longer essential and can begin to degenerate.
3
Throughout the remainder of pregnancy, the placenta continues producing rising levels of both estrogen and progesterone — with progesterone specifically working to suppress myometrial contractions, helping prevent premature labor.
4
Meanwhile, human placental lactogen promotes fetal growth and begins preparing the mammary glands for breastfeeding, while also inducing a degree of insulin resistance in the mother — a normal pregnancy adaptation that can occasionally progress to gestational diabetes.
Exam Application
Exams test whether you understand the luteoplacental shift (when the placenta takes over hormone production from the corpus luteum) and whether you can identify the roles of hCG, progesterone, estrogen, relaxin, and hPL at different stages of pregnancy.
⚠ Common Trap
The most common trap is assuming the corpus luteum continues producing hormones throughout pregnancy — after the luteoplacental shift (around week 10-12), the placenta itself takes over, and the corpus luteum's continued function is no longer necessary.
✓ Quick Self-Check
1. What hormone maintains the corpus luteum in early pregnancy, and where is it produced?
hCG, produced by the trophoblast.
Tap to reveal / hide
2. What is the luteoplacental shift, and when does it occur?
The transition where the placenta takes over progesterone and estrogen production from the corpus luteum, around week 10-12.
Tap to reveal / hide
3. What effect does progesterone have on the uterus during pregnancy, and why does this matter?
It suppresses myometrial contractions, which is essential for preventing premature labor.
Tap to reveal / hide
4. What does relaxin do?
Loosens pelvic ligaments and softens the cervix, in preparation for delivery.
Tap to reveal / hide
5. What does human placental lactogen (hPL) do?
Promotes fetal growth, prepares the mammary glands, and causes insulin resistance (diabetogenic effect).
Tap to reveal / hide