[Value of fetal scalp pH sampling early during the first stage of labour]

Objective: When fetal heart rate (FHR) abnormalities occur early during the first stage of labour, the risk of caesarean increases. In this study, we assessed the value of fetal scalp pH sampling on delivery mode, among women with FHR abnormalities before or at 5 cm cervical dilatation.

Methods: It is a retrospective observational study setting in a tertiary maternity center. All women with a live singleton cephalic fetus at term, who had a fetal scalp pH sampling, between January and July 2009, were included. We compared vaginal delivery and neonatal morbidity rates according to cervical dilatation at the time of the first fetal scalp pH sampling (≤ 5 or >5 cm). Neonatal morbidity was defined by pH at birth less or equal to 7.10 and/or 5 minutes Apgar score less or equal to 7 and/or neonatal transfer.

Results: During the study period, 108 women had at least one fetal scalp pH sampling, 8.5% of eligible women. Forty-six (42.6%) had a first pH at or before 5 cm cervical dilatation. The vaginal delivery rate was 62% and increased with increasing cervical dilatation at the time of the first fetal scalp pH (P<0.001). Among women who had fetal scalp pH early during the first stage of labour (≤ 5 cm), 50% delivered vaginally versus 71% when the fetal scalp pH was performed after 5 cm (P=0.026). The frequency of pH at birth less or equal to 7.10 was lower when the fetal scalp pH was performed before or at 5 cm (4.4% versus 16.9%, P=0.04). Neonatal morbidity rates were similar in both groups.

Conclusion: In this study, when FHR abnormalities occur early during the first stage of labour, use of fetal scalp pH sampling allows a vaginal delivery in half of cases without an increase in neonatal morbidity.