RESUMO
Maternal serum alpha-fetoprotein(MSAFP) has been a world wide screening test for open neural the tube defect. But elevation of MSAFP is related to not only neural tube defect, but also incorrect gestational age, congenital anomalies such as congenital nephrosis, esophageal and intestinal obstruction, low birth weight, oligohydroamnios, fetal death and chromosomal anomalies. If MSAFP is elevated, gestational age, congenital anomalies such as neural tube defect, multiple pregnancy and fetal death must be evaluated by ultrasound. When the ultrasound is nondiagnostic, amniotic fluid AFP(AFAFP) levels are measured and if AFAFP is elevated, presence or absence of aetylchoineststarase(AChE) is determined to rule out the false positive of amniotic AFP. Amniotic AChE test yielded detection rate of open spina bifida of 99%, 98% for anecephaly and a false-positive rate of 0.34%. We report a case with elevated AFAFP and positive amniotic AChE result in one fetus of the twin pregnancy conceived by ICSI and ZIFT, but in which targeted ultrasound findings were normal, maintained the pregnancy to term and normal twin was delivered by elective cesarean section.