A 29-year-old woman, gravida 2 para 1, comes to the office for an initial prenatal visit. The patient is at 16 weeks gestation by her last menstrual period and has had no contractions, vaginal bleeding, or leakage of fluid. For the first 2 months of her pregnancy, the patient had daily nausea and vomiting that resolved without treatment. She has no chronic medical conditions and has had no previous surgeries. Her only medication is a daily prenatal vitamin that she started taking a few weeks ago. The patient does not use tobacco, alcohol, or illicit drugs. Vital signs are normal. BMI is 30 kg/m². Cardiopulmonary examination is normal. The uterus measures 20 weeks gestation. Prenatal laboratory testing reveals that the patient's serum alpha-fetoprotein concentration is 3.8 multiples of the median (normal:

Question

A 29-year-old woman, gravida 2 para 1, comes to the office for an initial prenatal visit. The patient is at 16 weeks gestation by her last menstrual period and has had no contractions, vaginal bleeding, or leakage of fluid. For the first 2 months of her pregnancy, the patient had daily nausea and vomiting that resolved without treatment. She has no chronic medical conditions and has had no previous surgeries. Her only medication is a daily prenatal vitamin that she started taking a few weeks ago. The patient does not use tobacco, alcohol, or illicit drugs. Vital signs are normal. BMI is 30 kg/m². Cardiopulmonary examination is normal. The uterus measures 20 weeks gestation. Prenatal laboratory testing reveals that the patient's serum alpha-fetoprotein concentration is 3.8 multiples of the median (normal: <2.5). Which of the following is the best next step in management of this patient?

Quizplus · Accepted Answer

11ec25c8_da4e_ffd4_bc81_8f412fc6ad1d_MD0003_00 Neural tube defects (NTDs) are a common congenital anomaly and can vary from surgically correctable, minor defects (eg, spina bifida) to major defects (eg, anencephaly) that are incompatible with life. Screening for NTDs occurs at 15-20 weeks gestation with measurement of maternal serum alpha-fetoprotein (MSAFP), a glycoprotein produced by the fetus. MSAFP levels are reported in multiples of the median (MoM) using unaffected pregnancies at the same gestational age as reference. spina bifida anencephaly An abnormally elevated MSAFP level (≥2.5 MoM), as in this patient, suggests an NTD because AFP leaks more readily through a defect to become concentrated in the amniotic fluid and maternal circulation. However, an elevated level may also occur due to benign causes such as multiple gestation (ie, 2 fetuses each producing AFP) and incorrect gestational age dating (most common cause). These are both potential explanations in this patient with a uterine size-greater-than-dates discrepancy and late presentation to prenatal care. Therefore, an abnormal MSAFP level requires fetal ultrasound, which can detect multiple gestations, determine an accurate gestational age, and visualize fetal CNS structures. (Choice A) AFP and CA-125 are ovarian tumor markers, but both are commonly elevated in pregnancy. CA-125 levels are not measured in young patients (ie, those at low cancer risk) unless they have undergone surgery for ovarian cancer and require levels to follow disease progression. (Choice C) Folic acid supplementation is recommended starting ≥1 month before conception as the neural tube closes very early in pregnancy, often before patients are aware of being pregnant. However, increasing intake at 16 weeks gestation will not benefit this patient because neural tube closure is complete by 5-6 weeks gestation. In addition, increasing the dosage is not recommended because prenatal vitamins contain other components (eg, vitamin A) that are dangerous if taken in excess. (Choice D) A quantitative β-hCG level can be measured in the first trimester to evaluate for suspected abnormal pregnancies (eg, ectopic, hydatidiform mole). Second-trimester levels, which cannot assess fetal status, do not affect obstetric management. (Choice E) A repeat MSAFP level, even if normal, cannot exclude an NTD due to a tendency for values to regress to the mean, leading to a falsely reassuring result. Educational objective: Elevated maternal serum alpha-fetoprotein (MSAFP) levels can identify fetuses with neural tube defects but may be due to other benign causes (eg, multiple gestation, incorrect dating). Therefore, patients with elevated levels require fetal ultrasound. References: Screening for open neural tube defects. (http://www.ncbi.nlm.nih.gov/pubmed/27235920) ACOG practice bulletin no. 187: neural tube defects. (http://www.ncbi.nlm.nih.gov/pubmed/29189693)

A 29-Year-Old Woman, Gravida 2 Para 1, Comes to the Office