Prenatal screening for open neural tube defect (alpha-fetoprotein only), trisomy 21 (alpha-fetoprotein, human chorionic gonadotropin, estriol, and inhibin A) and trisomy 18 (alpha-fetoprotein, human chorionic gonadotropin, and estriol)
For an assessment that includes neural tube defect results, gestational age must be between 15 weeks, 0 days and 22 weeks, 6 days
Assessments for trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome) only are available between 14 weeks, 0 days and 22 weeks, 6 days
Initial or repeat testing is determined in the laboratory at the time of report and will be reported accordingly. To be considered a repeat test for the patient, the testing must be within the same pregnancy and trimester, with interpretable results for the same tests, and both tests are performed at Mayo Clinic
Race, weight, smoking, multiple fetus pregnancy, insulin-dependent diabetes (IDD), and in vitro fertilization (IVF) may affect marker concentrations. Black mothers tend to have higher alpha-fetoprotein (AFP) levels but lower risk of neural tube defects (NTD) and are assigned to a separate AFP median set. All multiples of the median (MoM) are adjusted for maternal weight (to account for dilution effects in heavier mothers). The AFP, estriol (uE3), and inhibin MoM are adjusted upward in IDD to account for lower values in diabetic pregnancies. Human chorionic gonadotropin (hCG) levels are higher and uE3 levels are lower in pregnancies conceived by IVF, MoM are adjusted accordingly to account for the alterations. Smoking results in higher second trimester maternal serum AFP and inhibin A levels and lower uE3 and hCG levels. MoM are adjusted accordingly to account for analyte differences in smokers
The estimated risk calculations and screen results are dependent on accurate information for gestation, maternal age, race, IDD, and weight. Inaccurate information can lead to significant alterations in the estimated risk. In particular, erroneous assessment of gestational age can result in false-positive or false-negative screen results. Because of its increased accuracy, the determination of gestational age by ultrasound is recommended, rather than by last menstrual period, when possible
A screen-negative result does not guarantee the absence of fetal defects. A screen-positive result does not provide a diagnosis but indicates that further diagnostic testing should be considered (an unaffected fetus may have screenpositive result for unknown reasons)
Valid measurements of AFP in maternal serum cannot be made after amniocentesis
Triplet and higher multiple pregnancies cannot be interpreted
Each center offering maternal serum screening to patients should establish a standard screening protocol that provides pre- and post-screening education and appropriate follow-up for screen-positive results
In a small percentage of samples, there is potential for alkaline phosphatase associated positive interference in the Beckman Access uE3 assay. This potential interference does not appear to be related to the amount of alkaline phosphatase in the patient sample. A falsely elevated unconjugated estriol (uE3)test result can lead to inaccurately underestimating the relative risk of chromosomal abnormalities, such as trisomy 21 and 18
