Snapshot A 36-year-old G1P2 woman returns to clinic for a regularly scheduled obstetric visit at 20 weeks. Two weeks ago, she had serum labs drawn for a quadruple screen. Her alpha-fetoprotein (AFP) level was found to be decreased. She undergoes further testing and evaluation for possible fetal genetic disorders. Introduction Overview measured routinely in maternal serum around 16-18 weeks (second trimester) assesses for neural tube defects or genetic conditions Associated conditions (abnormal AFP) neural tube defects trisomies abdominal wall defects Epidemiology 50/1,000 pregnant women have abnormal AFP 1-2/1,000 pregnant women will go on to deliver infants with related medical issues Pathogenesis Produced by yolk sac, gastrointestinal (GI) tract, and fetal liver Secreted by fetal kidney into amniotic fluid and passes through placenta into maternal serum High concentration in fetal life, minimal in adulthood Imaging Ultrasound indications abnormal AFP views transvaginal Studies Serum labs evaluate AFP in association with beta-human chorionig gonadotropin (β-hCG) pregnancy-associated plasma protein A (PAPP-A) inhibin A estriol Invasive amniocentesis indications uncertain or normal ultrasound findings after positive maternal serum alpha-feto protein (MSAFP) screen Differential Elevated maternal serum AFP neural tube defects anacephaly meningomyelocele encephalocele abdominal defects gastroschisis omphalocele twin gestations gestational age (GA) is older than was dated incorrect GA is most common cause of abnormal AFP Decreased maternal serum AFP Trisomy 21 (Downs syndrome) Trisomy 18 (Edwards syndrome) GA is younger than was dated