pH au scalp fœtal : intérêt pratique en salle de naissance

When should foetal pH measurements be performed after a prolonged deceleration? An experimental study in a fetal sheep model

OBJECTIVE

The aim of fetal heart rate monitoring during labour is to identify and prevent foetal distress, but its evaluation is not perfect. Fetal scalp blood sampling for pH measurement is one of the second-line methods of monitoring when fetal heart rate is classified as suspicious. This study aims to determine when pH testing should be performed after a prolonged deceleration.

STUDY DESIGN

This was an experimental study in a fetal sheep model. A partial umbilical cord occlusion was performed for seven minutes followed by a recuperation period of 30 min. Hemodynamic parameters (heart rate, mean blood pressure and intra-amniotic pressure) and blood gases were recorded before occlusion (T0), during occlusion (T4), just after the end of occlusion (T7), and then 10, 20 and 30 min after occlusion (T17, T27 and T37 respectively).

RESULTS

Ten experiments were carried out. During partial cord occlusion, the fetal pH decreased significantly to acidosis. After a prolonged deceleration with fetal acidosis, the pH recovered to a normal value, defined by a pH greater than or equal to 7.25, after 20 min of recuperation.

CONCLUSION

After a prolonged deceleration, fetal pH normalizes between 20 and 30 min thereafter. Thus, if a foetal blood sample is indicated, this delay must be respected in order to avoid inducing an unnecessary intervention decision.

[Fetal scalp pH during labor: Which threshold for intervention?]

OBJECTIVE

In case of abnormal fetal heart rate, there is no consensus on the decision threshold pH scalp leading to a rapid birth. The objective of this study was to compare neonatal issues and cesarean rate in two maternity using different decision thresholds of scalp pH.

MATERIAL AND METHODS

A comparative retrospective study conducted in two level III maternity units between January 2013 and May 2014, one maternity unit used a decision threshold of 7.20 (maternity unit 7,20), and the other one a threshold of 7.25 (maternity unit 7,25). An adverse neonatal outcome was defined by a composite endpoint of neonatal morbidity. The risk of cesarean was assessed using a multivariate analysis.

RESULTS

One hundred and four patients were included in the maternity unit 7,20 and 163 patients in the maternity 7,25. Adverse neonatal outcome was similar in both maternities (25% vs. 30,1%; P=0.4). The average pH at birth was similar in both maternities, as well as the Apgar score at 5minutes and neonatal transfer rates. However, BE<-12 was more frequent in maternity using 7,20 scalp pH threshold (7% vs. 0%; P<0.01). The cesarean rate was higher in maternity 7,25 (adjusted OR=2.23 95% CI [1.17-4.25]).

CONCLUSION

It seems that a decisional threshold fixed to 7,20 could be used reasonably. It could allow to reduce cesarean rate. Other studies are, however, needed to confirm that such threshold of 7,20 does not increase the risk of severe acidosis.