Prenatal diagnosis in diabetic gravidas: utility of ultrasound and maternal serum alpha-fetoprotein screening.

The differences in both the biology of pregnancy and the content of routine care between gravidas with and without diabetes mellitus lead to important differences in the potential utility of both ultrasound examination and maternal serum alpha-fetoprotein (MSAFP) screening. However, both diagnostic methods have become standards of care for these patients, without critical evaluation. This study examines the utility of both ultrasound and MSAFP in diabetic women. Four hundred thirty-two women with diabetes mellitus antedating pregnancy were examined sonographically between 12-23 weeks' gestation. Of these, 393 were also screened with MSAFP determinations. At delivery, 32 of these fetuses were found to have 38 major congenital malformations. All fatal or potentially life-threatening defects had been diagnosed in utero by sonography before 24 weeks' gestation. Ultrasound had a positive predictive value of 90% and a negative predictive value of 97% for identification of major birth defects before 24 weeks' gestation. There were 14 MSAFP values greater than 2.0 multiples of the median, and nine of these patients elected to undergo amniocentesis. Maternal serum alpha-fetoprotein screening had a positive predictive value of 17% and a negative predictive value of 94%. No malformations were detected through MSAFP screening that had not been diagnosed by sonography. No malformations missed sonographically were detected by MSAFP screening, and none of the amniocenteses were helpful diagnostically. We conclude that MSAFP screening is of minimal utility for diagnosing major congenital malformations in a high-risk population examined universally by an experienced sonographer.