Objective: To investigate maternal serum unconjugated oestriol (uE3) and human chorionic gonadotrophin (hCG) levels in pregnant women with insulin-dependent diabetes mellitus and to consider the implications of the results for antenatal screening for Down's syndrome.
Design: Descriptive study using stored antenatal serum samples.
Setting: Stored serum samples collected from women receiving routine antenatal care in Oxford.
Subjects: 126 singleton pregnancies in 92 women with insulin-dependent diabetes mellitus and for each pregnancy, two pregnancies without diabetes matched for gestational age and duration of storage of the serum sample. None of the pregnancies was associated with fetal neural tube defect or Down's syndrome.
Main study measures: Maternal serum uE3 and hCG levels at 15-22 weeks gestation. Alpha-fetoprotein (AFP) levels were also measured for comparison.
Results: The median uE3 level in the diabetic pregnancies was 0.92 multiples of the median (MoM) for pregnancies without diabetes at the same gestational age (P less than 0.05); and the hCG level was 0.95 MoM (P = 0.48). The median AFP level was also reduced to 0.77 MoM (P less than 0.001).
Conclusion: The reduction in uE3 and AFP levels in insulin-dependent diabetic pregnancies is sufficiently great to be taken into account in maternal serum screening programmes for Down's syndrome. Dividing the uE3 and AFP levels in such pregnancies by the corresponding median for insulin-dependent diabetic pregnancies will yield a similar false-positive rate in pregnancies with and without insulin-dependent diabetes mellitus.