••• Chapter 3^ Physiology of Normal Pregnancy^25
❍ When does the corpus luteum stop producing progesterone in pregnancy?
7 to 8 weeks of gestation.
❍ Name two consequences of excessive luteinization of the ovary.
This may result in theca lutein cysts or a pregnancy luteoma.
❍ What is the daily rate of progesterone production in third trimester singleton pregnancy?
250 mg/day.
❍ How is progesterone synthesized in the human placenta?
Two-step reaction. Cholesterol is converted to pregnenolone in mitochondria by cytochrome P450 side-chain cleavage
enzyme. Pregnenolone is converted to progesterone in microsomes by 3b-hydroxysteroid dehydrogenase, d 5–4 isomerase.
❍ What is the primary source of cholesterol for placental progesterone synthesis?
Maternal plasma low-density lipoprotein (LDL) cholesterol (90%).
❍ What is the principal estrogen found in the plasma and urine of pregnant women?
Estriol.
❍ What are the major forms of estriol present in the amniotic fluid?
16-glucosiduronate or 3-sulfate-16-glucosiduronate. 3-sulfate is also present in small quantities.
❍ Which hormone is decreased significantly after fetal death, umbilical cord ligation, and in anencephalic fetuses?
Estrogen. However, measurements of estriol to predict fetuses at risk have not been shown to change perinatal
morbidity or mortality.
❍ What is the average weight and volume of the nonpregnant uterus?
Average weight is 40 to 70 g with a volume of 10 mL.
❍ What is the average weight and volume of the pregnant uterus at term?
Average weight is 1100 to 1200 g with a volume of 5 L.
❍ What types of cellular changes occur during uterine enlargement in pregnancy?
Hypertrophy and stretching of existing muscle. Hyperplasia is very limited. Hypertrophy results from the actions
of estrogen and progesterone and occurs mostly before 12 weeks. The increase in uterine size after 12 weeks results
from pressure from expanding products of conception.
❍ How many layers of muscle are in the uterus? Describe them.
Three:
(1) An external layer that arches over the fundus to insert into the various ligaments.
(2) A middle layer of multidirectional interlacing muscle fibers between which extend blood vessels.
(3) An inner layer consisting of sphincter like fibers around the orifices of the tubes and internal os.