Which of the following are functions of the trophoblast cells in early pregnancy? Select all that apply.

Trophoblast function is central to early pregnancy, beginning immediately after blastocyst implantation. These cells differentiate into cytotrophoblasts and syncytiotrophoblasts, which invade the endometrial lining, allowing for implantation and formation of the placenta. Syncytiotrophoblasts secrete human chorionic gonadotropin (hCG), which supports the corpus luteum to maintain progesterone levels until placental steroidogenesis is established. Trophoblasts are not involved in surfactant production or neural development. Normal hCG levels in early pregnancy double approximately every 48–72 hours and peak around 100,000 mIU/mL by 10 weeks gestation.

Rationale for correct answers

A. Trophoblasts, specifically syncytiotrophoblasts, secrete hCG starting at implantation. hCG maintains the corpus luteum during early pregnancy, which secretes progesterone to support the endometrium.

B. Trophoblast cells give rise to the placenta, forming both fetal components such as the chorionic villi and contributing to maternal-fetal interface development.

E. Trophoblasts penetrate the endometrial epithelium, enabling implantation of the blastocyst. This process involves enzymatic digestion of maternal tissue and establishment of early uteroplacental circulation.

Rationale for incorrect answers

C. Surfactant is produced by type II alveolar cells in the fetal lungs starting around weeks 24–28, not by trophoblasts. It reduces surface tension in alveoli to aid postnatal lung expansion.

D. Neural tube closure is a function of the ectoderm, occurring around days 21–28 post-fertilization. Trophoblasts are extraembryonic cells and do not contribute to neuroectodermal development.

Take home points

• Trophoblasts facilitate implantation by invading maternal endometrium.

• They secrete hCG to maintain the corpus luteum and progesterone production.

• Trophoblasts form the fetal component of the placenta.

• They are not involved in neural or pulmonary development.

Fundal height measurement is a non-invasive clinical tool used to assess uterine growth and indirectly estimate fetal development. It is measured in centimeters from the pubic symphysis to the top of the uterine fundus. From weeks 18 to 32, the fundal height in centimeters typically equals the gestational age in weeks ±2 cm. Before 20 weeks, the uterus gradually rises through the abdomen. By 16 weeks, the fundus is typically located midway between the pubic symphysis and the umbilicus, and the expected measurement is approximately 14–18 cm.

Rationale for correct answers

B. At 16 weeks gestation, the uterus has ascended into the abdomen, and the expected fundal height is between 14 and 18 cm. This corresponds anatomically to a position halfway between the pubic symphysis and the umbilicus.

Rationale for incorrect answers

A. A fundal height of 8–10 cm is expected at approximately 12 weeks gestation, when the uterus is still just palpable above the pubic symphysis. At 16 weeks, this measurement would indicate uterine growth lag.

C. A measurement of 20–22 cm correlates with about 20–22 weeks gestation. At this point, the fundus is typically at the level of the umbilicus, not applicable to a 16-week pregnancy.

D. A fundal height of 24–26 cm is appropriate for 24–26 weeks gestation, when the fundus is well above the umbilicus. This would be significantly advanced for a 16-week pregnancy and may indicate incorrect dating or conditions like polyhydramnios.

Take home points

• Fundal height in cm generally matches gestational age in weeks between 18–32 weeks.

• At 16 weeks, fundal height should be 14–18 cm and located midway between symphysis and umbilicus.

• Lower-than-expected height may indicate fetal growth restriction or incorrect dating.

• Higher-than-expected height may suggest multiple gestation or polyhydramnios.