THE INFLUENCE OF GENERAL MATERNAL WEIGHT ON SERUM ALPHA-FETOPROTEIN AND FREE BETA-HUMAN CHORIONIC GONADOTROPIN LEVELS DURING THE SECOND TRIMESTER OF PREGNANCY

Objective: Maternal serum alpha-fetoprotein (AFP) and free beta-human chorionic gonadotropin (beta-hCG) levels are useful biomarkers for antenatal screening of Down syndrome, Trisomy 18 and open neural tube defects. The objective of this study was to investigate the relationship between maternal weight and serum AFP and free beta-hCG concentrations. Methodology: The study included 70 normal singleton pregnancies (mean age: 31.45 years) without any congenital anomalies, were screened using AFP, free beta-hCG and unconjugated estriol between 16 and 20 weeks of gestation, during January 2010 to July 2012, using enzyme linked immunosorbent assay (ELISA; AFP-hCG-uE3 AccuBind VAST ELISA Kit, USA), followed by the PregSafe prenatal risk assessment software. Results: The mean maternal weight was 59.75 [+ or -] 18.02 kg in studied pregnant women during the second trimester. There was a markedly inverse relationship between maternal weight and serum AFP and free beta-hCG levels. The median AFP and free beta-hCG level for women weighing [less than or equal to] 50 kg were respectively 90.4% and 57.4% higher than the median level for women weighing 70 kg or more. The overall variation in AFP (p = 0.17) and free beta-hCG (p = 0.69) levels were significant between these two weight groups. The reference interval (2.5 to 97.5 percentile) for AFP and free beta-hCG were obtained 5.56-136.37 ng/ mL and 4.41-283.55 IU/mL respectively. Conclusion: Maternal weight may affect the AFP and free beta-hCG concentrations during the second trimester. Heavier pregnant women have lower median values, perhaps as a result of a diluting effect of larger blood volume. A revision of the reference interval for AFP and free beta-hCG considering the body weight might improve in assessing risk of poor outcome, especially in heavier women.