Fetal Blood Sampling in early labour: is there an increased risk of operative delivery and fetal morbidityBJOG 2011;118:849-855

A Critical appraisal byMojisola OniahNidhi Nandan03/06/11

Aims and Objectives• To determine whether the rate of caesarean section was

increased in women who had FBS in early labour• To gain experience in critically appraising a retrospective

cohort paper

Introduction• Fetal blood sampling(FBS) plays a part in assessing fetal well-

being during labour.• Sensitivity for the prediction of fetal compromise is

significantly increased by its use.• FBS significantly reduces the rate of emergency caeserean

section for fetal distress• It is an invasive procedure done in the left lateral position. It

requires passing an amnioscope into the cervix in the presence of ruptured membranes.

• The fetal scalp is incised and blood is collected into a heparinized capillary tube. The sample is then analyzed to determine the fetal Ph and base excess.

• It is taken that a result of >7.20 is normal and anything less than that should prompt immediate delivery.

Clinical Question

•Does Fetal Blood Sampling in early labour increase the risk of operative delivery and fetal morbidity?

Guidelines• NICE guidelines recommend that FBS be performed in the

presence of a ‘Pathological’ CTG where delivery is contemplated because of the abnormal fetal heart pattern.

• Data from the 1990s suggest that FBS is used in about 5% of labours

Paper selected• Heazell A, Riches J,Hopkins L, Myers J. Fetal blood

sampling(FBS) in early labour: is there an increased risk of operative delivery and fetal morbidity? BJOG 2011;118:849-855

• Paper was selected because we didn’t have much time but we wanted to analyse a paper that was current, relevant and easy to analyse.

Aim of the study• They hypothesized that women undergoing FBS in early labour

(cervical dilatation <3cm) were less likely to achieve a vaginal delivery than women undergoing FBS in established labour (cervical dilatation >4cm)

• They also hypothesized that repeat FBS was not associated with an increased rate of operative delivery or adverse neonatal outcomes.

• The objective of the study was to analyze a group of consecutive women who underwent FBS in labour to address these hypotheses and to determine whether repeated FBS was associated with poorer neonatal outcomes.

Methods• A retrospective cohort study.• Women undergoing FBS in labour at 2 hospitals: Royal

Blackburn Hospital and St Mary's Hospital Manchester.• Time scale: March 2008 – June 2009• A minimum sample size of 380 women was calculated on the

basis that approximately 12% of women would have an FBS at <3cm.

Methods• Case notes were identified using patient hospital no obtained

from the blood gas analyser.• The case notes were then obtained and relevant data

collected.• Statistical analysis was carried out using spss v16.0.

Details of the Study

Flow chart for women in early labour(<3cm) undergoing multiple FBS and the no of women delivered as a result of fetal compromise

Outcomes of labours • 31% of women had CS (37.3% cat1), 36.7%had instrumental delivery

and 32.4% had a spontaneous vaginal delivery.• 48.4%of women who had FBS performed at 3cm had a vaginal

delivery compared with 71.9% of women who were >4cm at there first FBS.

• The proportions of nulliparous women (59.1%) who required FBS in early labour and were ultimately delivered by CS was higher that that of parous women(36.4%)

• Women who required 2 or more FBS(n=147) had an odds ratio for CS of 1.71(95% CI 1.37-2.13) compared to those requiring a single sample(n=234).

• Of women giving birth vaginally the odds ratio for instrumental delivery compared with normal delivery was not statistically significant for women undergoing first FBS at 3cm dilation or for 2 or more FBS.

Fetal outcomes• All babies were born alive.• Mean birthweight 3360g and 5.8% had a BW <2500g.• There was no significant differences in umbilical Ph and BE

values between women with first FBS at <3cm and those at >4cm dilatation.

• 23 (6.9%)infants were admitted to NICU.• There was no increased likelihood of NICU admission for a first

FBS at <3cm• Infants undergoing >3 FBS were slightly more likely to be

admitted to NICU(OR 2.69;95% CI 1.09-6.64)

Critical appraisal• Did the study address a clearly focused issue? YES: they wanted to see if FBS in early labour was associated

with an increased risk of operative delivery and fetal morbidity.

• Did the authors use an appropriate method to answer their question?

YES: Used a retrospective cohort study

Critical Appraisal• Was the cohort recruited in an acceptable way? YES: No of women who had FBS performed was collected

from the blood gas analyser machines on the delivery suite.No of women for the study was adequate• Was the exposure accurately measured to minimize bias? As it was a retrospective study all the women in the cohort

group had a FBS performed and recorded and this would minimise bias

• Was the outcome accurately measured to minimise bias? YES: The outcome was

• Have the authors identified all important confounding factors?

YES: They looked at demographics-age, ethnicity, BMI, parity, gestation, whether labour was induced, previous caeserean section.

They considered the fact some patients might have that other factors precipitating the need for C/S eg Failure to progress, and the fact that an FBS may not have been performed for other reasons like unable to get sample or the patient declined the procedure.

• Didn’t consider maternal illness or fetal complications

• Was the follow up of subjects complete enough? Cant tell: From the study we cant tell in terms of neonatal

morbidity how long the babies were followed up

• What are the results of the study? This study has shown that women commencing FBS

in early labour(i.e < 3cm cervical dilatation), or requiring 2 or more FBS procedures, have an increased risk of proceeding to caesarean section rather than vaginal delivery.• How precise is the estimate risk? For the women undergoing FBS in early labour the

incresed risk of delivery by C /S compared to those in established labour is modest(OR 1.71; 95%CI 1.04-3.13)

Similarly , women undergoing 2 or more FBS were at increased risk of C/S(OR 1.71; 95% CI 1.37-2.13)

• Do you believe the results? YES

• Can the results be applied to the local population? YES:

• Do the results of the study fit with other available evidence?

Conclusion