Which hormones characterize the first, second, and third trimesters, respectively?

• A. First: b-HCG; Second: Estriol; Third: Progesterone
• B. First: Estradiol; Second: hCG; Third: Estriol
• C. First: Progesterone; Second: hCG; Third: Estrogen
• D. First: hCG; Second: Progesterone; Third: Estradiol

Answer: (A)

The hormones that dominate each stage of pregnancy reflect where they come from and what they’re doing. In early pregnancy, beta-hCG is the key signal because it is produced by the developing placenta to maintain the corpus luteum and its production of progesterone, which supports the early pregnancy. As pregnancy progresses and the placenta takes over hormone production, estriol becomes the main placental estrogen, rising as the fetus grows and placental function expands. In the final months, progesterone stays high to keep the uterus relaxed and to support the ongoing pregnancy, helping prevent premature contractions. So the sequence—hCG in the first trimester, estriol in the second, and progesterone in the third—fits the physiological pattern of sources and roles across gestation.