Using Down syndrome serum screening results to predict low birthweight.

OBJECTIVE: To investigate the use of prenatal maternal serum screening results for Down syndrome, for the prediction of low (<2500 g) and very low (<1500 g) birthweight. DESIGN: Record linkage of maternal serum screening results with the corresponding birth records. PARTICIPANTS: 42 259 women whose pregnancies had been screened for the risk of Down syndrome. SETTING: Three East London maternity units, between February 1989 and August 1998. RESULTS: Estimates were made of the effectiveness of single markers only for the prediction of low birthweight, and of multiple markers together with mother's weight and smoking habit. As reported previously, high levels of the single markers alpha-fetoprotein and total human chorionic gonadotrophin, inhibin A, and low levels of unconjugated oestriol were associated with low birthweight. However, the best prediction was obtained when multiple serum markers comprising alpha-fetoprotein, unconjugated oestriol, and inhibin A were used in combination together with mother's weight and adjustment for smoking habit. For a false-positive rate of 5%, this combination predicted 23% of low birthweight and 39% of very low birthweight babies, possibly the best method of prediction to date. CONCLUSION: Prediction of low birthweight derived from Down syndrome screening could be used, for little extra cost, to advise on place of delivery or to select candidates for randomised clinical trials of low birthweight prevention.