In particular, erroneous assessment of gestational age can result in false-positive or false-negative screen results.
Because of its increased accuracy, we therefore recommend determination of gestational age by ultrasound, rather than by maternal dates alone when possible.
Follow up: Upon receiving maternal serum screening results, all information used in the risk calculation should be reviewed for accuracy (ie, weight, diabetic status, gestational dating, etc.).
If any information is incorrect the laboratory should be contacted for a recalculation of the estimated risks.
Increased maternal serum AFP values also may be seen in multiple pregnancies and in unaffected singleton pregnancies in which the gestational age has been underestimated.
Lower maternal serum AFP values have been associated with an increased risk for genetic conditions such as trisomy 21 (Down syndrome) and trisomy 18.
Risks for these syndrome disorders are only provided with the use of multiple marker screening (QUAD / Quad Screen [Second Trimester] Maternal, Serum).
Measurement of maternal serum AFP values is a standard tool used in obstetrical care to identify pregnancies that may have an increased risk for NTD.
Ultrasound is recommended to confirm dates for NTD screen-positive results.
If ultrasound yields new dates that differ by at least 7 days, a recalculation should be considered.
If dates are confirmed, high-resolution ultrasound and amniocentesis (including amniotic fluid AFP and acetylcholinesterase measurements for NTDs) are typically offered.
Subsequently, the AFP reaches the maternal circulation; thus producing elevated serum levels.
Other fetal abnormalities such as omphalocele, gastroschisis, congenital renal disease, esophageal atresia, and other fetal distress situations such as threatened abortion and fetal demise also may show AFP elevations.