Fetal blood sampling in early labour: is there an increased risk of operative delivery and fetal morbidity?

OBJECTIVE: To determine whether the rate of caesarean section was increased in women undergoing fetal blood sampling (FBS) in early labour. DESIGN: Retrospective study. SETTING: Secondary and tertiary obstetric units in the UK. POPULATION: A cohort of 381 women undergoing FBS. METHODS: Data relating to demographics, labour and delivery characteristics, and neonatal outcomes were collected on women undergoing FBS in labour. Odds ratios (ORs) for caesarean section compared with vaginal delivery for women who had their first FBS in early labour (≤ 3 cm cervical dilatation) and for women who required multiple samples were calculated. MAIN OUTCOME MEASURES: Mode of delivery. RESULTS: Forty-eight percent of women who required their first FBS at a cervical dilatation of ≤ 3 cm achieved a vaginal delivery; these women were at modestly increased risk of caesarean section (adjusted OR 1.80; 95% CI 1.04-3.13) compared with women who had their first FBS at a cervical dilatation of ≥ 4 cm. The odds ratio for caesarean section in women who required two or more FBS was 1.71 (95% CI 1.37-2.13) compared with those requiring a single sample. There were no differences in instrumental delivery. Infants undergoing three or more FBS were more likely to be admitted to a neonatal intensive care unit (NICU; OR 2.69; 95% CI 1.09-6.64), although this was not associated with increased acidaemia. CONCLUSIONS: Women who require FBS in early labour or multiple FBS are at a modestly increased risk of caesarean section compared with those in established labour. When contemplating FBS at ≤ 3-cm cervical dilatation, practitioners should not be put off by the perceived low chance of vaginal delivery, but repeating FBS on more than three occasions should be considered carefully.