What is the primary role of the placenta during fetal development?

Folic acid supplementation is critical for preventing neural tube defects (NTDs) such as spina bifida and anencephaly, which arise from failure of neural tube closure by day 28 post-conception. Folate, a B-vitamin (B9), is required for DNA synthesis, methylation, and cell division. Since neural tube formation occurs early, often before pregnancy is confirmed, supplementation should begin at least 1 month prior to conception. The recommended daily intake for women of childbearing age is 400 mcg (0.4 mg) of folic acid. For women with a history of NTDs or high-risk conditions (e.g., diabetes, antiseizure therapy), the dosage increases to 4 mg daily.

Rationale for correct answers

C. The CDC and WHO recommend 400 mcg of folic acid daily for all women of childbearing potential to reduce the risk of NTDs. This amount ensures adequate folate status for early embryonic neural tube closure, which completes by the 4th week of gestation.

Rationale for incorrect answers

A. 100 mcg is insufficient for NTD prevention. This dose may be found in food but is below the therapeutic threshold required for reducing neural tube malformations.

B. 200 mcg is still subtherapeutic. Evidence-based guidelines consistently show that at least 400 mcg per day is needed for effective neural tube defect risk reduction.

D. 800 mcg is above the general recommendation. While not harmful in most cases, this higher dose is reserved for special populations or prenatal supplements and is not routinely recommended for all women unless otherwise indicated.

Take home points

• The neural tube closes by day 28; early folic acid intake is essential.

• 400 mcg daily is recommended for all women of reproductive age.

• Higher doses are used in women with prior NTD-affected pregnancies or high-risk conditions.

• Folate is vital for DNA synthesis and embryonic cell division.

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.