TAKING ACCOUNT OF VAGINAL BLEEDING IN SCREENING FOR DOWNS-SYNDROME

Objective To derive a method for revising the risk of Down's syndrome in maternal serum marker screening when there is vaginal bleeding. The effect on screening performance of routinely allowing for the presenc e or absence of bleeding in all women is also assessed. Design Overvie w of published studies on the rate of reported vaginal bleeding in pre gnancies with Down's syndrome, on the rate according to maternal age a nd on the association of bleeding with alpha-fetoprotein (AFP) level. The publications are supplemented with data on unconjugated oestriol ( uE(3)), human chorionic gonadotrophin (hCG) and AFP levels in a consec utive series of screened women. Setting Routine Down's syndrome screen ing tests carried out on women having antenatal care at the St James's University Hospital, Leeds. Subjects Eight hundred and nine screened women. Results In five studies the rate of vaginal bleeding in Down's syndrome pregnancies was 1.7 times that in unaffected pregnancies on a verage. In three studies, the vaginal bleeding rate increased proporti onally by 2.2 % on average for each year of maternal age. Three studie s and our own data were consistent with a 10% increase in the mean AFP level associated with vaginal bleeding, but it did not appear to mate rially alter uE(3) and hCG levels or the standard deviations and corre lation coefficients for any of the three analytes. An individual woman 's risk was calculated by multiplying her age-specific odds of Down's syndrome by two likelihood ratios, one relating to the vaginal bleedin g itself and one from the marker levels. Routine allowance for the pre sence or absence of vaginal bleeding was estimated to increase the det ection rate by less than 1%. Conclusion Our method is of clinical valu e in revising the risk when there is concern that vaginal bleeding mig ht be responsible for a negative maternal serum Down's syndrome screen ing result. A policy of routinely incorporating information on vaginal bleeding in risk estimation for all women would have too small an eff ect on overall screening performance to recommend it.