Use of fetal scalp blood lactate for assessing fetal well-being during labour

A fetal heart rate that is abnormal or not reassuring during labour may be caused by the inability of the baby to adapt to decreases in oxygen supply during the birth. Inadequate oxygen supply may lead to the development of acidosis (low pH levels) and increased lactate in the blood. After the amniotic membranes have ruptured and the cervix dilated to around 3 cm, it is possible to measure lactate (or pH) levels in a sample of blood taken from the baby's scalp. A much smaller amount of blood is needed for the lactate test than to measure pH. This review identified two studies of 3348 mother-baby pairs that compared lactate and pH testing in labour. Lactate testing was more likely to be successful than pH testing, but with no differences in newborn outcomes, including the number of babies with low Apgar scores, low pH in their cord blood or admissions to the neonatal intensive care nursery. There were no differences in the number of mothers having caesarean sections, forceps or vacuum births between the two groups. We conclude that lactate testing in labour may be more likely to be successfully achieved than pH testing.

Authors' conclusions: 

When further testing to assess fetal well-being in labour is indicated, fetal scalp blood lactate estimation is more likely to be successfully undertaken than pH estimation. Further studies may consider subgroup analysis by gestational age, the stage of labour and sampling within a prolonged second stage of labour. Additionally, we await the findings from the ongoing studies that compare allocation to no fetal blood sample with sampling for lactate and address longer-term neonatal outcomes, maternal satisfaction with intrapartum fetal monitoring and an economic analysis.

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Background: 

Fetal scalp blood sampling for lactate estimation may be considered following identification of an abnormal or non-reassuring fetal heart rate pattern. The smaller volume of blood required for this test, compared with the more traditional pH estimation, may improve sampling rates. The appropriate use of this practice mandates systematic review of its safety and clinical effectiveness prior to widespread introduction.

Objectives: 

To evaluate the effectiveness and risks of fetal scalp lactate sampling in the assessment of fetal well-being during labour, compared with no testing or alternative testing.

Search strategy: 

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 January 2015).

Selection criteria: 

All published and unpublished randomised and quasi-randomised trials that compared fetal scalp lactate testing with no testing or alternative testing to evaluate fetal status in the presence of a non-reassuring cardiotocograph during labour.

Data collection and analysis: 

We used the standard methodological procedures of the Cochrane Pregnancy and Childbirth Group. Two review authors independently assessed the studies.

Main results: 

The search identified two completed randomised controlled trials (RCTs) and two ongoing trials. The two published RCTs considered outcomes for 3348 mother-baby pairs allocated to either lactate or pH estimation of fetal blood samples when clinically indicated in labour. Overall, the published RCTs were of low or unclear risk of bias. There was a high risk of performance bias, because it would not have been feasible to blind clinicians or participants.

No statistically significant between-group differences were found for neonatal encephalopathy (risk ratio (RR) 1.00, 95% confidence interval (CI) 0.32 to 3.09, one study, 2992 infants) or death. No studies reported neonatal seizures. We had planned to report death with other morbidities, for example, neonatal encephalopathy; however, the data were not available in a format suitable for this, therefore death due to congenital abnormality was considered alone. The three reported neonatal deaths occurred in babies with diaphragmatic hernias (n = 2) or congenital cardiac fibrosis (n = 1). All three babies had been randomised to the pH group and were not acidaemic at birth.

There were no statistically significant differences for any of the pre-specified secondary fetal/neonatal/infant outcomes for which data were available. This included low Apgar score at five minutes (RR 1.13, 95% CI 0.76 to 1.68, two studies, 3319 infants) and admission to neonatal intensive care units (RR 1.02, 95% CI 0.83 to 1.25, one study, 2992 infants), or metabolic acidaemia (RR 0.91, 95% CI 0.60 to 1.36, one study, 2675 infants) considered within the studies, either overall or where data were available for those where fetal blood sampling had occurred within 60 minutes of delivery.

Similar proportions of fetuses underwent additional tests to further evaluate well-being during labour, including scalp pH if in the lactate group or scalp lactate if in the pH group (RR 0.22, 95% CI 0.04 to 1.30, two studies, 3333 infants;Tau² 1.00, I² = 58%). Fetal blood sampling attempts for lactate and pH estimation were successful in 98.7% and 79.4% of procedures respectively in the one study that reported this outcome.

There were no significant between-group differences in mode of birth or operative birth for non-reassuring fetal status, either for all women, or within the group where the fetal blood sample had been taken within 60 minutes of delivery (for example, caesarean section for all enrolled, RR 1.09, 95% CI 0.97 to 1.22, two studies, 3319 women; operative delivery for non-reassuring fetal status for all enrolled RR 1.02, 95% CI 0.93 to 1.11, one study, 2992 women).

Neither study reported on adverse effects of fetal scalp lacerations or maternal anxiety.

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