A 31-year-old woman, gravida 1 para 0, at 19 weeks gestation comes to the office to discuss results of a serum alpha-fetoprotein (AFP) screening. The patient has been followed since her seventh week of pregnancy, when gestational age was confirmed with transvaginal ultrasound. Since learning that women should start taking folic acid prior to becoming pregnant to avoid congenital defects, she has been concerned about the possibility of having a baby with a neural tube defect. Because she started taking folic acid after the first trimester and one of her friends has a child with spina bifida, she requested testing of her AFP levels. The patient has no chronic medical conditions or previous surgeries. Family history is not significant. She does not use tobacco, alcohol, or illicit drugs. Vitals signs are within normal limits. The uterus is palpable below the umbilicus. Fetal heart rate is 155/min by bedside Doppler ultrasound. The serum AFP level is slightly elevated at 3.0 MoMs (normal:

Question

A 31-year-old woman, gravida 1 para 0, at 19 weeks gestation comes to the office to discuss results of a serum alpha-fetoprotein (AFP) screening.  The patient has been followed since her seventh week of pregnancy, when gestational age was confirmed with transvaginal ultrasound.  Since learning that women should start taking folic acid prior to becoming pregnant to avoid congenital defects, she has been concerned about the possibility of having a baby with a neural tube defect.  Because she started taking folic acid after the first trimester and one of her friends has a child with spina bifida, she requested testing of her AFP levels.  The patient has no chronic medical conditions or previous surgeries.  Family history is not significant.  She does not use tobacco, alcohol, or illicit drugs.  Vitals signs are within normal limits.  The uterus is palpable below the umbilicus.  Fetal heart rate is 155/min by bedside Doppler ultrasound.  The serum AFP level is slightly elevated at 3.0 MoMs (normal: <2.5).  A repeat AFP is elevated at 3.1 MoMs.  Which of the following is the most appropriate next step in management of this patient?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c03a_c440_8f63_09a4559665bb_MD0005_00 Maternal serum alpha-fetoprotein (AFP) levels are measured at 15-20 weeks gestation as a screening test for a variety of fetal anomalies. AFP is synthesized by the fetus and excreted by the fetal kidneys into amniotic fluid; although the function of AFP is unknown, there is an association between abnormal levels and fetal abnormalities. An elevated AFP level (>2.5 MoMs) is frequently present with neural tube defects (eg, open spina bifida, anencephaly) and ventral wall defects (eg, omphalocele, gastroschisis). The higher the MoM value, the higher the likelihood of detecting a fetal abnormality. Factors such as improper pregnancy dating and multifetal gestations can also raise the serum AFP level. open spina bifida anencephaly ventral wall defects In patients with an abnormal AFP level, the test is repeated, ensuring that all factors that could affect the value (eg, maternal weight, race) are correct. Subsequently, an obstetric ultrasound is performed to obtain a detailed anatomic survey, with attention given to identifying fetal malformations associated with elevated serum AFP. In the case of poor fetal dating or lack of prior ultrasound, an ultrasound helps clarify gestational age and number of fetuses. A normal AFP does not rule out all neural tube defects, as closed spina bifida may present with a normal value. If an obstetric ultrasound fails to identify a fetal malformation in a patient with elevated serum AFP levels, amniocentesis can be performed. Amniotic fluid AFP, along with acetylcholinesterase, is measured. Elevations in both predict a neural tube defect with a high positive predictive value (Choices B and C). (Choice A) Amniocentesis for fetal karyotype diagnoses chromosomal abnormalities (eg, aneuploidy), which typically present with abnormally low AFP levels. (Choice E) Maternal serum AFP screening has high sensitivity and specificity rates for neural tube and ventral wall defects. Patients with abnormal results require further evaluation to rule out an anomaly, rather than reassurance. Educational objective: Maternal serum alpha-fetoprotein levels can be increased in neural tube defects (eg, anencephaly, open spinal bifida) and ventral wall defects. Patients with elevated serum levels should undergo a detailed anatomic ultrasound. References: Role of maternal serum alpha-fetoprotein and ultrasonography in contemporary detection of spina bifida. (http://www.ncbi.nlm.nih.gov/pubmed/26332586) Screening for open neural tube defects. (http://www.ncbi.nlm.nih.gov/pubmed/27235920)

A 31-Year-Old Woman, Gravida 1 Para 0, at 19 Weeks