Objectives: To investigate whether, in women with abnormal uterine artery Doppler, platelet volume and function will identify a subgroup of women at increased risk of pre-eclampsia and intrauterine growth restriction and whether in-vitro platelet aggregation precedes the onset of clinical disease. Design: Platelet number, volume and aggregation induced by collagen or adenosine 5'-diphosphate were evaluated in 16 non-pregnant controls, 29 pregnant women with normal uterine artery Doppler and 31 pregnant women with abnormal Doppler, hence at risk of pre-eclampsia and intrauterine growth restriction at 23 weeks. Outcome of pregnancy was recorded in each case. Results: Twelve women in the group with abnormal uterine artery Doppler subsequently developed pre-eclampsia and/or intrauterine growth restriction. All women with normal uterine artery Doppler had a normal pregnancy outcome. No differences in platelet count or in vitro platelet aggregation induced by collagen were observed between the groups. Mean platelet volume was greater in those with abnormal Doppler who had intrauterine growth restriction or normal pregnancy outcome compared with normal Doppler (10.3 and 10.3 vs. 9.4 fL, P = 0.004 and P = 0.01, respectively). Aggregation induced by adenosine diphosphate was higher in women with abnormal Doppler who developed pre-eclampsia or intrauterine growth restriction compared with those with normal outcomes (66.5 and 66.5 vs. 21%, P = 0.02, P = 0.03, respectively). Conclusions Women with abnormal uterine artery Doppler at 23 weeks show alterations in mean platelet volume and platelet function that relate to subsequent adverse outcome.