SAN FRANCISCO — Adjustments made to maternal serum alpha fetoprotein values in pregnant diabetics may be inadequate to screen for neural tube defects or Down syndrome, Dr. Loralei L. Thornburg reported in a poster presentation at the annual meeting of the Society for Maternal-Fetal Medicine.
She and her associates studied data on 77 pregnant women with type 1 diabetes, 75 with type 2 diabetes, and 304 nondiabetic pregnant women with normal glucose levels who had maternal serum alpha fetoprotein (MSAFP) levels drawn between July 2001 and August 2003 at the same institution. MSAFP levels are used in prenatal screening for neural tube defects and Down syndrome. Previous studies have shown that MSAFP values are lower in type 1 diabetics than in nondiabetics, and MSAFP in type 2 diabetics is not well studied.
Usually clinicians apply a 20% upward adjustment of the MSAFP multiple-of-the-median value for pregnant type 1 diabetics, and they use a lower cut-off for normal to improve the sensitivity of screening for neural tube defects.
In the study population, a 10% correction factor appeared to be a more appropriate adjustment to MSAFP values in both type 1 and type 2 diabetics. In addition, correction for both diabetes and weight were needed to normalize MSAFP values, said Dr. Thornburg of the University of Rochester (N.Y.).
With the 20% correction factor, the MSAFP multiple-of-the-median value was significantly higher in both diabetic groups than in control patients. After the correction factor was decreased to 10% in the diabetes groups, the MSAFP multiple-of-the-median value did not differ significantly between the three groups. All medians were specific to gestational age and race. Fifty-five (73%) of patients with type 2 diabetes were on insulin therapy.
The MSAFP multiple-of-the-median values before correction for diabetes differed between patients with type 1 and type 2 diabetes until correction for weight.
Correction for weight and the 10% correction for diabetes were needed to control for significant differences between the control group and either diabetes group in MSAFP multiple-of-the-median values.
The retrospective study excluded patients with an MSAFP multiple-of-the-median value greater than 2.0, patients whose serum samples were drawn too early or redrawn, patients who underwent early chorionic villi sampling, and patients with fetal anomalies, aneuploidy, multiple gestations, or no information on diabetes type.