MATERNAL SERUM HCG AND FETAL NUCHAL TRANSLUCENCY THICKNESS FOR THE PREDICTION OF FETAL TRISOMIES IN THE FIRST TRIMESTER OF PREGNANCY

Objective To compare the potential value of maternal serum total hCG a nd 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 measure d in samples from 83 singleton pregnancies with fetal chromosomal abno rmalities (trisomy 21 (n = 41), trisomy 18 (n = 19), trisomy 13 (n = 8 ) sex chromosome aneuploidies (n = 11), triploidy (n = 4)) and 394 chr omosomally normal controls at 10 to 13 weeks gestation. In all cases, the fetal nuchal translucency thickness was measured at the time of fe tal 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 14 5 chromosomally normal fetuses with nuchal translucency 3 to 9 mm tota l hCG and free beta-hCG were not significantly different from the 249 with nuchal translucency less than 3 mm. In fetuses with trisomy 21, t otal hCG and free beta-hCG were significantly higher, whereas in triso mies 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 fo r trisomy 21 were 24% and 32%, respectively. There was no significant association between hCG and nuchal translucency thickness in either th e chromosomally normal (r = -0.01) or abnormal group (r = -0.15). Conc lusion An improved estimate of risk for fetal trisomies at 10 to 13 we eks gestation can be derived by combining data on maternal age, matern al serum total or free beta-hCG and fetal nuchal translucency thicknes s.