A 37-year-old woman, gravida 2, para 1, comes to the physician for a routine prenatal visit. Her estimated gestation age is 16 weeks based on last menstrual period. She has been married for 8 years and has a healthy 5-year-old son. The woman is healthy and has no relatives with genetic disorders, intellectual disability, developmental delay, or autism. She has been intermittently compliant with prenatal vitamins due to "morning sickness." Laboratory results are as follows: Which of the following fetal conditions is the most likely cause of these laboratory results?

Question

A 37-year-old woman, gravida 2, para 1, comes to the physician for a routine prenatal visit.  Her estimated gestation age is 16 weeks based on last menstrual period.  She has been married for 8 years and has a healthy 5-year-old son.  The woman is healthy and has no relatives with genetic disorders, intellectual disability, developmental delay, or autism.  She has been intermittently compliant with prenatal vitamins due to "morning sickness."  Laboratory results are as follows:  Which of the following fetal conditions is the most likely cause of these laboratory results?

Quizplus · Accepted Answer

11ec25c8_da26_69e4_bc81_9b7bd4ff46e7_MD0003_00 The maternal serum quadruple test is performed in the second trimester (15-20 weeks) and consists of maternal serum α-fetal protein (MSAFP), β-hCG, estriol, and inhibin A. Women age >35 are at increased risk of fetal aneuploidy. This patient's profile is most consistent with Down syndrome, which is caused by meiotic nondisjunction (trisomy 21) or Robertsonian translocation. Down syndrome has a profile of low MSAFP, low estriol, elevated β-hCG, and increased inhibin A level. The quadruple screen detects ~80% of fetuses with Down syndrome but has a false-positive rate of ~5%. Patients with abnormal quadruple screening results can be offered cell-free fetal DNA testing, which measures circulating, free maternal and fetal DNA in maternal plasma and has a sensitivity and specificity of up to 99%. An ultrasound should be performed to evaluate for fetal anomalies. (Choice A) Prenatal screening tests are less reliable with twins as multiple-gestation pregnancies produce more AFP. The other markers are an average from the fetuses and so abnormal markers from an affected fetus may be offset by the normal fetus. MSAFP is low in this patient, making multiple gestations unlikely. (Choices B and E) Increased MSAFP levels are associated with open neural tube defects and abdominal wall defects. Maternal folic acid deficiency is a risk factor for failure of primary neurulation, which can result in myelomeningocele. Gastroschisis is a paraumbilical bowel evisceration with no covering membrane; omphalocele is a peritoneum-covered sac at the umbilicus. The other screening markers are normal in these cases. (Choice C) Trisomy 18 is caused by meiotic nondisjunction and has a profile of low MSAFP, estriol, and β-hCG. Inhibin A level is typically normal. Educational objective: The maternal quadruple screen with increased levels of β-hCG and inhibin A and decreased levels of maternal serum alpha-fetoprotein (MSAFP) and estriol is suggestive of Down syndrome. Trisomy 18 is characterized by a normal inhibin A level and low MSAFP, estriol, and β-hCG. Open neural tube defects and abdominal wall defects cause an elevated MSAFP; the rest of the markers are normal. References: ACOG practice bulletin no 77: screening for fetal chromosomal abnormalities. (http://www.ncbi.nlm.nih.gov/pubmed/17197615)

A 37-Year-Old Woman, Gravida 2, Para 1, Comes to the Physician