24 Obstetrics and Gynecology Board Review •••
❍ When is hCG detectable in plasma of pregnant women?
8 to 9 days after ovulation.
❍ Name four physiologic actions of hCG.
(1) Maintenance of corpus luteum and continued progesterone production.
(2) Stimulation of fetal testicular testosterone secretion promoting male sexual differentiation.
(3) Stimulation of the maternal thyroid by binding to TSH receptors as its alpha-subunit is identical.
(4) Promotes relaxin secretion by the corpus luteum.
❍ During the second half of pregnancy, what effect do insulin-like growth factors (I&II) have on
adrenocorticotropic hormone (ACTH)?
IGF I&II are important in increasing adrenal responsiveness to ACTH.
❍ In early pregnancy (weeks 5–12), where is amniotic and maternal alpha-fetoprotein (AFP) produced?
Amniotic fluid AFP is mainly from the yolk sac, while maternal circulating AFP is from fetal liver.
❍ When do AFP levels peak in fetal blood?
At the end of the first trimester.
❍ Where can relaxin production be found other than by the corpus luteum?
Relaxin is also produced by the placenta and myometrium.
❍ What is the most highly produced substance generated by the placenta?
Human placental lactogen (hPL), otherwise known as human chorionic somatomammotropin (hCS) is produced
in amounts as high as 1 to 4 g/day.
❍ What are the functions of hPL?
(1) Lipolysis and an increase in the levels of circulating free fatty acids.
(2) Antiinsulin action leading to an increase in maternal levels of insulin providing mobilized sugars and amino acids.
❍ Is hPL required for successful pregnancy?
No. Probably is a backup mechanism to ensure fetal nutrient supply.
❍ What other two hormones are homologous to hPL?
Growth hormone (96% homology) and prolactin (67% homology).
❍ Where is hPL produced?
Cytotrophoblast and syncytiotrophoblast.
❍ What is the biologic half-life of hPL?
The half-life is 15 minutes.