Objective: To compare the potential value of maternal serum total hCG and free beta-hCG in predicting the risk for fetal trisomies during the first trimester of pregnancy and to examine whether data on maternal hCG and fetal nuchal translucency thickness can be combined to derive risks.
Methods: Maternal serum total hCG and free beta-hCG were measured in samples from 83 singleton pregnancies with fetal chromosomal abnormalities (trisomy 21 (n = 41), trisomy 18 (n = 19), trisomy 13 (n = 8) sex chromosome aneuploidies (n = 11), triploidy (n = 4) and 394 chromosomally normal controls at 10 to 13 weeks gestation. In all cases, the fetal nuchal translucency thickness was measured at the time of fetal karyotyping.
Results: In the 249 chromosomally normal controls with fetal nuchal translucency less than 3 mm, total hCG and free beta-hCG decreased significantly with increased fetal crown-rump length. In 145 chromosomally normal fetuses with nuchal translucency 3 to 9 mm total hCG and free beta-hCG were not significantly different from the 249 with nuchal translucency less than 3 mm. In fetuses with trisomy 21, total hCG and free beta-hCG were significantly higher, whereas in trisomies 18 and 13 levels were lower than in chromosomally normal controls. When the cutoff levels for total hCG and free beta-hCG were selected to include 4% of chromosomally normal fetuses, the detection rates for trisomy 21 were 24% and 32%, respectively. There was no significant association between hCG and nuchal translucency thickness in either the chromosomally normal (r = -0.01) or abnormal group (r = -0.15).
Conclusion: An improved estimate of risk for fetal trisomies at 10 to 13 weeks gestation can be derived by combining data on maternal age, maternal serum total or free beta-hCG and fetal nuchal translucency thickness.