FIRST-TRIMESTER MATERNAL SERUM ALPHA-FETOPROTEIN AS A MARKER FOR FETAL CHROMOSOMAL DISORDERS

We evaluated first-trimester maternal serum alpha-fetoprotein (MS-AFP) as a marker for fetal chromosomal disorders. The multicentre study wa s performed under the auspices of the Dutch Working Party on Prenatal Diagnosis. MS-AFP was measured in 2404 normal pregnancies and 72 chrom osomally abnormal pregnancies. The median multiple of the normal media n (MOM) in 32 Down's syndrome pregnancies was 0.83 with a 95 per cent confidence interval ranging from 0.60 to 1.04. The difference between the distributions of first-trimester MS-AFP in normal and Down's syndr ome pregnancies was statistically significant (t-test: t = 2.34, P < 0 .05). Thirty-one per cent of the Down's syndrome pregnancies were foun d below the tenth percentile. We found no difference between normal pr egnancies and pregnancies with other chromosomal disorders (eight case s with trisomy 18, MOM = 1.26; seven cases with sex chromosome abnorma lities, MOM = 1.07; 22 cases with a chromosomal mosaic pattern in chor ionic villi, MOM = 1.08). We conclude that first-trimester MS-AFP can discriminate between normal and Down's syndrome pregnancies, but is no t an effective marker. First-trimester MS-AFP has no value as a marker for other fetal chromosomal disorders.