Insulin-dependent diabetes mellitus and prenatal screening results: current experience from a regional screening programme.

From around 91,000 women having routine prenatal screening for Down's syndrome and neural tube defects between July 1992 and October 1995, 261 women were identified as having insulin-dependent diabetes mellitus (IDDM). Alpha-fetoprotein (AFP) and human chorionic gonadotrophin (hCG) levels were reduced in these women, with median levels of 0.89 and 0.91 multiples of the median (MOM), respectively. The IDDM patients had a median weight which was 6 kg heavier than that of non-IDDM women. After correction for maternal weight, the AFP and hCG levels in the IDDM patients were 0.98 and 0.92 MOM, respectively. In routine practice, using results which were not weight-corrected, the IDDM women were neither over- nor under-represented in the high-risk group for Down's syndrome, but showed a tendency to be under-represented in the high-risk group for neural tube defects.