A small amount also is transported from the amniotic cavity. Fetal AFP diffuses across the placental barrier into the maternal circulation. The concentration of AFP peaks in fetal serum between 10 to 13 weeks. By the end of the first trimester, nearly all of the AFP is produced by the fetal liver. A small amount also is produced by the gastrointestinal tract. If results are positive, the patient is typically offered counseling and diagnostic testing.ĪFP is a fetal protein that is initially produced in the fetal yolk sac and liver. The information from both trimesters is combined and a report is issued. The blood sample is tested for AFP, unconjugated estriol (uE3), human chorionic gonadotropin (hCG), and inhibin A.
If the risk from the first trimester is below the established cutoff, an additional serum specimen is collected in the second trimester for SEQB / Sequential Maternal Screening, Part 2, Serum. For a stand-alone NTD-risk assessment, order MAFP1 / Alpha-Fetoprotein (AFP), Single Marker Screen, Maternal, Serum. When the part 1 screen is completed, a NTD risk is not provided. In that event, the patient is typically offered counseling and diagnostic testing. If the result from part 1 indicates a risk for Down syndrome that is higher than the screen cutoff, the screen is completed and a report is issued. The results of the ultrasound measurement and blood work along with the maternal age and demographic information are used to calculate Down syndrome and trisomy 18 risk estimates. Along with the NT measurement, a maternal serum specimen is collected to measure pregnancy-associated plasma protein A. Therefore, NT data is accepted only from NT-certified sonographers. The ultrasound measurement, referred to as the NT measurement, is difficult to perform accurately. SEQA / Sequential Maternal Screening, Part 1, Serum involves an ultrasound and a blood collection. Sequential screening combines biochemical and ultrasound markers (nuchal translucency: NT) measured in both trimesters of the pregnancy. Sequential screening is a type of cross-trimester screening, which has an improved detection rate as compared to either first- or second-trimester screening. Various options for maternal serum screening are available and include: first trimester, second trimester, and cross-trimester. Maternal serum screening is used to identify pregnancies that may have an increased risk for certain birth defects, such as trisomy 21 (Down syndrome), neural tube defect (NTD) and trisomy 18.
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