A 25-year-old woman comes to the office due to amenorrhea. The patient's last menstrual period was 8 weeks ago, and she normally has regular, monthly menses. The patient has no chronic medical conditions and has had no surgeries. She takes no daily medications. Blood pressure is 100/60 mm Hg and pulse is 92/min. BMI is 24 kg/m². Abdominal examination shows a soft, nontender abdomen with no palpable masses. Pelvic examination shows an 8-week-sized, nontender uterus. Serum β-hCG level is elevated. Which of the following is the most important direct role of hCG in this patient?

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11ec160b_3b1e_d409_9249_2b8a2685a355_MD0001_00 Early pregnancy depends on hormonal feedback between the ovary, uterine endometrium, and embryo. In a normal menstrual cycle, ovulation (ie, oocyte release) creates the ovarian corpus luteum, which increases progesterone production to induce endometrial decidualization (ie, uterine lining thickening, formation of the decidua basalis) in preparation for both promotion and maintenance of embryonic implantation (Choice E). When the oocyte is fertilized, a blastocyst eventually develops and implants into the uterine decidua basalis approximately 6-7 days after fertilization. The outer cells of the blastocyst (ie, trophoblast) then differentiate into the cytotrophoblast and syncytiotrophoblast, which develop into the placenta. The syncytiotrophoblast invades the decidua basalis and secretes β-hCG into maternal circulation. β-hCG signals the ovary to maintain the corpus luteum and to continue progesterone production, which maintains both the decidualized endometrium and the pregnancy until the placenta has developed enough to completely take over progesterone production (typically by 10 weeks gestation). Following this luteal-placental transition, the corpus luteum degenerates, and the role of progesterone changes to maintain uterine quiescence (ie, inhibit contractions) (Choice B). (Choice A) Estrogen, not hCG, stimulates the anterior pituitary to produce prolactin during pregnancy. (Choice C) The process of embryonic cell division and differentiation begins before the formation of the placental syncytiotrophoblast, which secretes hCG; therefore, hCG does not cause embryonic cell division. Educational objective: β-hCG is a hormone secreted by the placental syncytiotrophoblast after uterine invasion that signals the ovary to maintain the corpus luteum, which produces progesterone in early pregnancy. __________ References: hCG: biological functions and clinical applications. (http://www.ncbi.nlm.nih.gov/pubmed/28937611)

A 25-Year-Old Woman Comes to the Office Due to Amenorrhea