MSAFP levels should generally be done at what gestational age?

Ans. C. 15 weeks. (Ref. Textbook of Obstetrics D.C. Dutta 7th Ed pg. 106; 493)MSAFP:# AFP is a oncofetal (Molecular wt 70,000).# it is produced by yolk sac and fetal liver.# Highest level in fetal serum and amniotic fluid is reached around 13 weeks and thereafter it decreases.# Maternal serum levels peak around 32 weeks of gastation.# MSAFP level is elevated in:- Wrong gestational age- Open neural tube defects- Multiple pregnancy- Rh iso- IUD- Anterior abdominal wall defects- Renal anomalies# Low levels are found in:- Trisomies (Down's syndrome)GTD# Test is done between 15-20 weeks. Triple test is also performed at 15-18 weeks. In Downs levels of MSAFP and UE3 tend to be low and while that of hCG high.# MSAFP value of 2.5 multiples of medians is taken as cut-off point.# Elevated MSAFP detects 85% of all neural tube defects.Prenatal diagnostic tests. MSAFPMSAFP, hCG, UE3 (Triple test)Beta-hCG + PAPP-A + NTSoft tissue marker (Nuchal translucency)1.Time (weeks)14-2014-1811-1411-142.ObservationMSAFP (y)MSAFP (ss), hCG (y), UE3 (ss)hCG (y),PAPP-A (ss)NT > 3 mm3.Anomaly to detectOpen NTDDown's syndromeDown's syndromeDown's syndrome, Turner's syndrome and others4.CommentCut off level of 2.5 MOM can detect 90% of anencephaly, 80% open spina bifida.A cut off value of 1 in 200, is screen positive.A cut off value 1 in 300 is screen positive.Detection of Down's syndrome is high (92%), when NT and NB are combined.5.Detection rate65%73%85-89%70-80%6.False positive rate3-5%5%5%5-6%