NBME Obstetrics and Gynecology 3

Question 1

A 26-year-old G1P0 at 16 weeks undergoes amniocentesis. Results show markedly elevated amniotic fluid AFP and a positive acetylcholinesterase. What is the most likely diagnosis?

Accepted Answer

Open neural tube defect

Answer

Elevated amniotic AFP combined with positive acetylcholinesterase is diagnostic of an open neural tube defect, confirming fetal neural tissue is exposed to amniotic fluid.

Question 2

A 24-year-old at 28 weeks with gestational diabetes has a growth ultrasound showing estimated fetal weight at the 97th percentile with a disproportionately large abdominal circumference. This finding is most directly caused by which fetal mechanism?

Accepted Answer

Fetal hyperinsulinemia causing increased fat deposition

Answer

Maternal hyperglycemia leads to fetal hyperinsulinemia, which acts as a growth factor causing macrosomia through increased fat and glycogen deposition.

Question 3

A 34-year-old G2P1 at 11 weeks has first-trimester screening showing nuchal translucency of 4.2 mm, elevated free β-hCG, and low PAPP-A. This pattern is most consistent with which chromosomal abnormality?

Accepted Answer

Trisomy 21 (Down syndrome)

Answer

Increased NT, elevated free β-hCG, and decreased PAPP-A is the classic first-trimester combined screen pattern for trisomy 21.

Question 4

A 29-year-old Rh-negative woman at 28 weeks has a negative antibody screen and has not previously received Rh immunoglobulin. What is the appropriate management?

Accepted Answer

Administer Rh immunoglobulin now and again within 72 hours of delivery

Answer

Unsensitized Rh-negative women should receive 300 mcg Rh immunoglobulin at 28 weeks and again postpartum to prevent alloimmunization.

Question 5

A 30-year-old woman at 36 weeks is GBS-positive and has a reported history of anaphylaxis to penicillin. GBS susceptibilities are available. What is the correct intrapartum antibiotic prophylaxis regimen?

Accepted Answer

Clindamycin IV if the isolate is susceptible

Answer

For penicillin allergy with high anaphylaxis risk, clindamycin is used if the GBS isolate is susceptible; if resistant or unknown, vancomycin is given.

NBME Practice Test

NBME Practice Test

NBME Obstetrics and Gynecology 3