Maternal Serum AFP

A screen negative result means the fetus is unlikely to have an open neural tube defect (ONTD). This test is not diagnostic and should not replace second-trimester ultrasound screening for neural tube defects (NTDs). Maternal serum AFP alone does not evaluate risk for fetal chromosome abnormalities.

A screen positive result means the risk for a fetal neural tube defect is increased, but it could also indicate an increased risk for fetal abdominal wall defects, fetal nephrosis, fetal demise, and pregnancy complications. Inaccurately estimated gestational age (GA) can also lead to false-positive AFP screening results.

Patients with screen positive results should discuss their results and follow up care with their healthcare provider. The American College of Obstetricians and Gynecologists (ACOG) recommends that all patients with screen positive results be referred for genetic counseling and fetal ultrasound examination, and amniocentesis should be considered.¹  

The GA is derived from the estimated date of delivery (EDD) reported. For the most accurate estimate of GA, the earliest ultrasound-derived EDD should be used.²

The earliest ultrasound-derived EDD should be used for dating purposes.² An ultrasound-derived EDD is most accurate when determined in the first trimester.

• If a first-trimester ultrasound EDD is available and is within ±7 days of the GA used for the screening test, the GA should not be changed for screening purposes.
• If a second-trimester EDD is available and the GA is  ±10 days of the EDD used for screening, the GA should not be changed for screening purposes.
• If the GA used for screening is outside the ultrasound EDD range, it may be appropriate to change the GA used for screening.²

To change the EDD or GA used for a specific patient’s screening test, please contact your local Quest Diagnostics laboratory or call Quest Genomic Client Services at 1.866.GENE.INFO (1.866.436.3463). 

Alpha-fetoprotein (AFP) concentrations seen in NTD-affected and unaffected singleton pregnancies are well known; therefore, an adjusted AFP multiples-of-median (MoM) can be used to calculate an NTD risk in singleton pregnancies.

However, AFP concentration data in twin and triplet pregnancies are insufficient to allow accurate NTD risk calculations. Results for twin and triplet pregnancies are reported as screen positive or screen negative, but an NTD risk is not provided.

Please, call Quest Genomics Client Services at 1.866.GENE.INFO (1.866.436.3463) to talk with a genomic science specialist. Documentation of the abnormality in the family may enable a more specific risk assessment.