38 Obstetrics and Gynecology Board Review •••
❍ Which form of vitamin D is increased in pregnancy and why?
The activated form 1,25-dihydroxyvitamin D is increased in pregnancy with nonpregnant values doubling to a
range of 75 to 100 pg/mL. This is a PTH-related mechanism. As PTH increases, the hydroxylation of 25-vitamin
D at the 1 position is increased at the level of the kidney. In addition, vitamin D-binding protein also increases in
pregnancy, which may increase 1,25 vitamin D levels.
❍ Does PTH and/or calcitonin cross the placenta?
Neither hormone crosses the placenta.
❍ Which of the substances produced by the adrenal cortex are decreased in pregnancy?
Dehydroepiandrosterone sulfate (DHEAS) remains unaltered or slightly decreased through extensive
16 alpha-hydroxylation. All other products (sex steroids, cortisol, and aldosterone) increase.
❍ If testosterone is increased in the maternal serum, why is the female fetus not masculinized?
Total testosterone is doubled from nonpregnancy levels of 0.5 mg/L to 1.0 mg/L. Free testosterone levels are
decreased in pregnancy by about one half. Little or no testosterone enters the fetal circulation as testosterone. There
is complete conversion of testosterone to 17b-estradiol by the trophoblast. This has been documented in women
who have very high testosterone levels due to androgen secreting tumors.
❍ Describe the ACTH response to pregnancy.
ACTH levels rise in pregnancy after an initial decrease early in pregnancy. The levels rise despite a dramatically
increased cortisol level (three times nonpregnancy values). This is a paradox postulated to be due to a resetting of
the feedback system secondary to tissue refractoriness to cortisol.
❍ A pregnant patient complains that her contact lenses are painful to wear recently. Is this normal?
Yes. Corneal thickness increases in pregnancy and can cause discomfort when wearing lenses fitted before
pregnancy.
❍ Is vision affected by pregnancy?
Visual acuity remains the same; however, a transient loss of accommodation has been reported during pregnancy
and lactation.
❍ Which hormones, aside from hCG, increase the most in pregnancy?
Hormone Increase
Human placental lactogen (hPL) 5000-fold
Progesterone 1000-fold
Estradiol 400-fold
Prolactin 10-fold