Maternal serum alpha-fetoprotein levels in second trimester of normal pregnancies.

Meternal serum alpha fetoprotein (MS-AFP) was used as a method of screening for neural tube defects since 1973. The cut off levels for further investigation varies depending upon many factors such as the maternal race, the place of residence and the gestational age. This study was carried out in 503 normal pregnant Thai women in order to indentify the level of maternal serum AFP during 13-21 weeks. This study included only normal pregnancies and normal fetal outcome. The median, 97th , 99th percentile of MSAFP were calculated to be used for the screening test of neural tube defects in Thai pregnant women.