NEW YORK (Reuters Health) – In pregnant women with type 1 or type 2 diabetes, maternal serum alpha-fetoprotein (AFP) values require routine upward adjustment during second-trimester screening for congenital defects, new research suggests.
Decreased levels of maternal AFT during the second trimester are associated with increased risk of Down syndrome, while elevated values are associated with open neural tube defects, Dr. Loralei L. Thornburg and colleagues note in the August issue of the American Journal of Obstetrics and Gynecology.
Currently, a standard 20% adjustment factor is often applied to patients with type 1 diabetes, but there is disagreement as to whether adjustments for maternal weight and type 2 diabetes status are necessary.
To clarify these issues, the research team at the University of Rochester Strong Memorial Hospital in New York conducted a case-control study of patients who underwent second-trimester AFP screening. Included were 77 subjects with type 1 diabetes, 75 with type 2 diabetes, and 304 nondiabetic control subjects.
Mean values for AFP multiples of the median differed significantly among the three groups: 1.06 among controls, 0.86 among type 1 diabetics and 0.70 among type 2 diabetics (p < 0.0001).
After correction for weight, values did not differ between the two diabetic groups (0.92), but were still lower than in controls (1.01, p = 0.009).
Further correction using a 10% adjustment for diabetes eliminated differences between groups, while application of the standard 20% correction factor resulted in overcorrection of AFP values.
“Decreasing the correction factor to 10% should both improve the positive predictive value of testing for neural tube defects and minimize the false-negative screening rate for Down syndrome,” Dr. Thornburg’s team suggests, “although a much larger cohort with outcome data would be necessary to make this assessment.”
Am J Obstet Gynecol 2008;199:135.e1-135.e5