Ultrasound-adjusted risk and spectrum of fetal chromosomal abnormality in women with elevated maternal serum alpha-fetoprotein.

OBJECTIVE: To determine the incidence of chromosomal abnormality in sonographically normal fetuses after amniocentesis for elevated maternal serum alpha-fetoprotein (MSAFP), and to compare the spectrum of abnormality with that seen in women undergoing amniocentesis for advanced maternal age.

METHODS: Cytogenetic and sonographic findings from women undergoing amniocentesis for elevated MSAFP (at least 2.0 multiples of median) between 1988-1992 were reviewed retrospectively. The literature was reviewed and data compiled regarding the risk of chromosomal abnormality for women with elevated MSAFP levels.

RESULTS: The incidence of abnormal karyotype among all women with elevated MSAFP was 1.23% (nine of 733). The risk of an abnormal karyotype with a normal ultrasound examination was 1.01% (seven of 696). This included three fetuses with sex chromosome abnormalities, three with de novo, apparently balanced rearrangements, and one with an unbalanced structural rearrangement.

CONCLUSIONS: The risk of chromosomal abnormality in nonselected patients, predominantly younger than 35 years of age, with elevated MSAFP and a sonographically normal fetus is 0.6%, based on a compilation of our data and reports published previously. The spectrum of abnormality in women with elevated MSAFP differs from that in women of advanced maternal age. Patients should be specifically counseled regarding this difference.