Maternal urine alpha-fetoprotein concentrations between 14 and 21 weeks of gestation.

BACKGROUND: The aim of this study was to ascertain the normal range of the midtrimester maternal urine alpha-fetoprotein (AFP) concentrations in Taiwanese pregnancies. METHODS: AFP was measured in the urine samples, obtained before genetic amniocentesis, from 268 women with normal singleton pregnancies between 14 and 21 weeks of gestation. Week-specific median values for urine AFP/creatinine (Cr) were calculated by weighted linear regression after log transformation and the data were converted to units in the multiple of the median (MoM). The gestational age in all cases was determined by ultrasound parameters. RESULTS: The levels of urine AFP and AFP/Cr increased gradually with advancing gestational age. The AFP/Cr MoM values of singleton pregnancies after log transformation showed a normal distribution with a mean (standard deviation) of 0.0071 (0.3228). The median, 10th and 90th centiles of AFP/Cr were 0.98, 0.43 and 3.61 MoM, respectively. Of the pregnant Taiwanese women studied, 4.9% (13/268) and 16% (43/268) had urine AFP/Cr MoM levels less than 0.31 MoM and 0.5 MoM respectively. CONCLUSION: The establishment of a reference range which allows for gestational differences in AFP/Cr levels is essential for further antenatal testing.