Background Fetal blood sampling (FBS) is undertaken to identify fetal academia and the need to expedite delivery. Currently, there are few data regarding the outcome of labour when a FBS is required in early labour (≤3 cm) or when multiple samples are required.

Methods A retrospective study of 381 women undergoing FBS in labour in a 1-year period in two obstetric units was undertaken. OR for Caesarean section (CS) when FBS began prior to 3 cm cervical dilatation, and when multiple samples were required were calculated. OR were adjusted for confounding variables.

Results Women requiring FBS at cervical dilatation ≤3 cm at first sample were at moderately increased risk of CS (OR 1.71, p<0.001, 95% CI 1.37 to 2.13). There was no increased risk of instrumental delivery in this group (OR 0.51, CI 0.18 to 1.15) There was no significant effect of age, parity, body mass index or gestation. 63 (16.5%) of patients required three or more FBS; repeated FBS was not associated with increased CS (OR 0.52, CI 0.22 to 1.26) or instrumental delivery (OR 1.66, CI 0.88 to 3.30). There was no increased neonatal academia or admission to NICU in infants with ≥3 FBS.

Conclusion Women who require FBS in early labour are at a moderately increased risk of CS compared to those in established labour. Women who require multiple FBS are at no increased risk of CS or instrumental delivery. When contemplating FBS at 3 cm dilated, practitioners should not be put off by a perceived low chance of vaginal delivery or concerns about repeated FBS.