A 23-year-old woman, gravida 1, para 0, comes to the office for a routine prenatal care visit. She is at 35 weeks gestation and feels well. She reports regular fetal movement and no contractions, loss of fluid, or vaginal bleeding. Pregnancy to date has been uncomplicated and the patient has no underlying medical conditions. She signed up for a clinical trial investigating prolactin. At 34 weeks gestation, she had a serum prolactin level several times higher than what was recorded prior to pregnancy. Which of the following hormones prevents lactation in this patient?

Question

A 23-year-old woman, gravida 1, para 0, comes to the office for a routine prenatal care visit.  She is at 35 weeks gestation and feels well.  She reports regular fetal movement and no contractions, loss of fluid, or vaginal bleeding.  Pregnancy to date has been uncomplicated and the patient has no underlying medical conditions.  She signed up for a clinical trial investigating prolactin.  At 34 weeks gestation, she had a serum prolactin level several times higher than what was recorded prior to pregnancy.  Which of the following hormones prevents lactation in this patient?

Quizplus · Accepted Answer

Progesterone and estrogen promote normal development and maternal breast growth during the prenatal period. In the first trimester of pregnancy, progesterone is secreted by the corpus luteum and is crucial to successful implantation. In the second and third trimesters, progesterone is produced by the placenta and suppresses FSH and LH though action on the anterior pituitary (Choice C). Prolactin is a peptide hormone that promotes lactogenesis (ie, maturation of breast alveolar cells) and milk production. It is released by the anterior pituitary gland due to stimulation by thyrotropin-releasing hormone (TRH) and increases steadily in circulation as pregnancy progresses. Although lactogenesis may begin during the second trimester, lactation is suppressed due to the high progesterone levels inhibiting the binding of prolactin to receptors on breast alveolar cells. After delivery, the precipitous drop in progesterone allows prolactin to stimulate lactation. (Choice A) β-hCG is secreted by the embryonic syncytiotrophoblast during the first trimester, rising to its highest levels at the ninth week of gestation. β-hCG serves to maintain the corpus luteum until the placenta can assume responsibility for estrogen and progesterone synthesis. By mid-pregnancy, the corpus luteum degenerates and serum β-hCG decreases to a very low level. Therefore, β-hCG is not likely to have a significant effect on lactation during late pregnancy. (Choices B and E) Thyroxine and insulin contribute to normal gestational mammary gland hypertrophy. Although high dose thyroxine can decrease the production of TRH, this patient has an elevated prolactin level which indicates that TRH production is not suppressed. Educational objective: In pregnancy, progesterone is secreted by the corpus luteum and later by the placenta. Although prolactin secretion increases as pregnancy progresses, high progesterone levels inhibit lactation by preventing binding of prolactin to receptors on alveolar cells in the breast. __________ References: Prolactin secretion patterns: basic mechanisms and clinical implications for reproduction (http://www.ncbi.nlm.nih.gov/pubmed/20733016)

A 23-Year-Old Woman, Gravida 1, Para 0, Comes to the Office