First-trimester screening for trisomy 21 using alpha-fetoprotein.

OBJECTIVE To investigate the potential value of adding maternal serum alpha-fetoprotein (AFP) to free β-human chorionic gonadotropin (β-hCG) and PAPP-A and fetal nuchal translucency (NT) thickness in first-trimester screening for trisomy 21. METHODS In this case control study, serum AFP was measured in 100 trisomy 21 and 1,500 euploid pregnancies in which screening for trisomy 21 had been performed by a combination of serum free β-hCG and PAPP-A and fetal NT at 11-13 weeks' gestation. We examined the effect of adding AFP on the performance of screening by the combined test. RESULTS In the trisomy 21 pregnancies, the median multiple of the normal median AFP, adjusted for gestational age, maternal weight, racial origin, smoking status and method of conception, was significantly reduced (0.7037, 95% CI: 0.6398-0.7739). Adding AFP to the combined test improved the performance of screening and for a risk cut-off of 1 in 100, the false-positive rate was reduced from 2.8 by 0.4% (95% CI: 0.13-0.77%) without a significant change in detection rate. CONCLUSIONS Inclusion of serum AFP improves the performance of the first-trimester combined test in screening for trisomy 21.