What is the primary role of human chorionic gonadotropin (hCG) in early pregnancy?
Stimulates fetal lung maturation
Maintains the corpus luteum
Promotes fetal weight gain
Initiates labor contractions
The Correct Answer is B
Human chorionic gonadotropin (hCG) is a glycoprotein hormone produced by syncytiotrophoblasts of the developing placenta beginning around day 6–8 post-fertilization. Its primary role in early pregnancy is to maintain the corpus luteum, which in turn secretes progesterone to sustain the endometrial lining and prevent menstruation. hCG levels double every 48–72 hours in a viable early pregnancy, peaking around 100,000 mIU/mL by weeks 8–11, then gradually decline. Normal range at 4 weeks gestation is approximately 5–426 mIU/mL. hCG also promotes immune tolerance, supports placental growth, and is the basis for urine and serum pregnancy tests.
Rationale for correct answers
B. hCG maintains the corpus luteum during the first 8–10 weeks of pregnancy, ensuring continued secretion of progesterone, which is essential for maintaining the decidua and preventing uterine contraction. Without hCG support, the corpus luteum would regress and lead to pregnancy loss.
Rationale for incorrect answers
A. Fetal lung maturation is not influenced by hCG. This function is regulated by cortisol and surfactant production, which are stimulated by glucocorticoids such as betamethasone during the third trimester.
C. Fetal weight gain occurs primarily in the third trimester and is regulated by placental nutrient transfer, insulin-like growth factors, and maternal nutrition, not by hCG.
D. Labor contractions are initiated by increased oxytocin, prostaglandins, and estrogen at term. hCG has no role in triggering parturition.
Take home points
• hCG maintains corpus luteum function in early pregnancy to support progesterone production.
• Peak hCG levels occur between weeks 8–11 and decline thereafter.
• hCG is the hormone detected in pregnancy tests.
• It is produced by syncytiotrophoblast cells of the trophoblast.
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Related Questions
Correct Answer is B
Explanation
Fetal eyelid development follows a defined timeline that reflects neurological and anatomical maturation. The eyelids fuse by approximately week 10 to protect the developing eye and remain fused to allow for proper corneal and conjunctival differentiation. By around week 26, the eyelids separate, allowing the fetus to open and close the eyes in response to light and other stimuli. This milestone is associated with optic nerve myelination and increasing visual system activity, though vision remains immature. The retina is still developing, and light perception is limited. This separation coincides with increased blink-startle responses and maturation of REM-like eye movements.
Rationale for correct answers
B. Separation of the eyelids typically occurs by week 26, allowing the fetus to begin opening its eyes. This marks a significant milestone in fetal neurological and sensory development, including initiation of visual reflexes and responses to light.
Rationale for incorrect answers
A. Taste bud development begins much earlier, around weeks 7–8, and by week 14, taste receptors are already functional. While taste sensation continues to mature, this is not a unique milestone of week 26.
C. Formation of fingerprints (dermal ridges) is completed by weeks 17–19, during the second trimester. This unique feature arises due to genetic and intrauterine influences on skin patterning.
D. Complete lung maturation does not occur by week 26. Type II alveolar cells begin surfactant production around weeks 24–28, but full structural and functional lung maturity typically is not achieved until week 36–37.
Take home points
• Fetal eyelids fuse around week 10 and reopen by week 26.
• Eye opening indicates sensory and CNS maturation.
• Fingerprints form between weeks 17–19, earlier than eye opening.
• Lung maturation continues into late third trimester.
Correct Answer is ["A","B","C","D"]
Explanation
Embryonic organogenesis occurs during weeks 3–8 of gestation, a period marked by rapid cellular differentiation, morphogenesis, and high vulnerability to teratogens. During this stage, the three germ layers—ectoderm, mesoderm, and endoderm—differentiate into major organ systems. The central nervous system forms from the ectoderm beginning with neural tube closure by day 28. The cardiovascular system is the first functional organ system, with the primitive heart beating by day 22. Limb buds appear by week 4, followed by elongation and digital separation. The digestive system originates from endoderm, with gut tube formation by week 4. The reproductive system, although genetically determined early, structurally differentiates later, during the fetal period.
Rationale for correct answers
A. The central nervous system begins developing early in the embryonic period. The neural plate forms in week 3, and the neural tube closes by week 4, initiating brain and spinal cord development.
B. The cardiovascular system starts forming in week 3. By day 22, the primitive heart tube begins beating and circulates blood, making it the earliest functioning organ system.
C. Limb buds become visible by week 4. By week 8, limb differentiation is advanced, including the formation of digits through programmed cell death (apoptosis) in the hand and foot plates.
D. The digestive system begins forming in week 4 from the endodermal germ layer. The primitive gut is divided into foregut, midgut, and hindgut, which later give rise to organs like the stomach, intestines, and liver.
Rationale for incorrect answers
E. The reproductive system, while genetically established at fertilization (XX or XY), begins structural differentiation later, primarily during the fetal period (after week 9). Gonadal development becomes histologically apparent between weeks 10–12.
Take home points
• Organogenesis occurs between weeks 3–8, known as the embryonic period.
• CNS, cardiovascular, digestive, and limb development all begin during this stage.
• The heart starts beating by day 22, making it the first functioning organ.
• Reproductive organs differentiate structurally later, during the fetal period.
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