Second-trimester prenatal screening markers for Down syndrome in women with insulin-dependent diabetes mellitus.

Published studies have shown that some serum markers used in screening for Down syndrome tend to be lower among women with insulin-dependent diabetes mellitus (IDDM). On this basis, many screening programmes adjust the marker levels to take account of this difference. Recent studies suggested that the marker levels were not different, and so adjustment may no longer be needed, possibly because of better diabetic control. Data from a prenatal screening programme for Down syndrome were examined to see whether the median values of second-trimester screening markers were still reduced in pregnant women with IDDM. A total of 366 women with IDDM singleton pregnancies without Down syndrome were identified from the screening programme at Barts from 1989 to 2002. After allowing for maternal weight, the median multiples of the median (MoM) for IDDM-unaffected singleton pregnancies were as follows: 0.88 (95% confidence interval 0.84-0.93) for alphafetoprotein (AFP), 0.95 (0.91-0.99) for unconjugated oestriol (uE3), 0.90 (0.80-1.01) for total human chorionic gonadotrophin (total hCG), 0.98 (0.88-1.08) for free beta-hCG, and 0.99 (0.89-1.10) for inhibin-A. The median levels for AFP and uE3 were statistically significantly lower in pregnant women with IDDM. The other markers were not significantly different in women with and without IDDM. There remains a case for adjusting AFP and uE3 levels in women with IDDM in prenatal screening programmes for Down syndrome.