OBJECTIVE The aim of this study was to investigate the effect of cordocentesis on fetomaternal hemorrhage (FMH). METHODS One hundred and three diagnostic cordocenteses, without any other associated procedure, were performed at 23-40 weeks' gestation. FMH was detected using the Kleihauer-Betke staining of maternal blood taken immediately before and after cordocentesis. RESULTS Significant FMH occurred after 40 (38.8%) of the 103 procedures. An increased risk of fetal bleeding was associated with both an anterior placenta (odds ratio (OR) 5.89; 95% confidence interval (CI) 2.27-15.3; p < 0. 001) and a transplacental cordocentesis (OR 37.0; 95% CI 2.15-636; p < 0.001). The volume of FMH was greater after cordocentesis with an anterior placenta (90th percentile 6.20 ml) than after cordocentesis with a lateral (90th percentile 4.58 ml) or posterior placenta (90th percentile 1.35 ml) (p < 0.001). After fetal blood sampling, significant FMH occurred more frequently with a procedure duration of 3 min or more (OR 4.45; 95% CI 1.70-11.7; p = 0.002) and with two or more needle insertions (OR 4.65; 95% CI 1.80-12.1; p = 0.001). CONCLUSIONS FMH following cordocentesis may be related to placental injuries. This event is influenced by placental location, procedure duration and the number of needle insertions.