Induction of labour does not increase the risk of caesarean delivery in pregnant women with a larger than average baby.
This is based on a review of four trials of 1190 women with a suspected large baby who were allocated either to have labour induced from 38 weeks or to watchful waiting.
Induction did not increase the risk of most negative outcomes for the baby, such as bleeding in the brain, or mother, such as major tearing. However, these outcomes are rare, so a larger number of women would need to be studied to be confident in these findings. When mothers were not induced babies were larger and born about a week later than if they were induced. They did suffer from more fractures, which can be a complication of delivering a larger baby.
Current NICE guidelines on induction of labour recommend only offering induction at 41 or 42 weeks in otherwise healthy women who have a larger than average baby.
This analysis suggests that earlier induction is likely to be safe and may be an option for women to consider.
Why was this study needed?
The term macrosomia describes a large foetus or baby whose weight is greater than the 90th percentile for the duration of pregnancy. It occurs in about 2 to 10% of births at term in the UK. The size of the baby can be estimated using ultrasound, with an estimated weight of 4000g or more a commonly used threshold for diagnosing macrosomia.
Pregnant women, with larger than average babies, may be more likely to have a caesarean delivery or a difficult birth. This can result in unwanted outcomes for the mother, such as prolonged labour, and the infant, such as nerve damage. This led to the idea of inducing labour in such women rather than watchful waiting, but the effect on maternal and infant outcomes was not clear.
This review aimed to evaluate the benefits and potential harms of induction for women with a large baby.
What did this study do?
This systematic review and meta-analysis assessed whether induction at 38 weeks’ gestation or later increased the risk of caesarean delivery or negative outcomes, compared with expectant management, in pregnant women with larger than average babies.
It comprised three randomised controlled trials from high income countries and one UK unpublished pilot randomised controlled trial from 1998. These studies included 1190 pregnant women whose babies had an estimated weight of 4000g or more, or above the 95th percentile.
The analyses were driven by one large trial of 818 women. This trial was the only source of data for a number of outcomes and had higher than UK average rates for shoulder dystocia, where one or both shoulders get stuck because they had a low threshold for diagnosis.
There were too few women in the review to be certain of any effect of induction on rare maternal or foetal harms, such as perinatal death, brain haemorrhage or brachial plexus palsy, a type of nerve damage.
What did it find?
- The incidence of normal vaginal delivery was similar in both groups, at 60.3% for induction and 55.4% for expectant management (RR 1.09, 95% CI 0.99 to 1.20).
- The incidence of caesarean delivery was similar in the induction of labour group (26.6%) and the expectant management group (29.4%). Induction did not influence the risk of caesarean delivery (relative risk [RR] 0.91, 95% confidence interval [CI] 0.76 to 1.09).
- Time to delivery was about a week less in the induction group (mean difference -7.55 days, 95% CI -8.20 to -6.89 days).
- Compared with expectant management, induction did not significantly increase the risk of negative maternal outcomes such as operative vaginal delivery (13% versus 15.2%: RR 0.86, 95% CI 0.65 to 1.13), perineal tear requiring stitching (36.4% versus 38.4%), anal sphincter tear (1.4% versus 0.5%) or blood transfusion (1.0% versus 0.7%).
- Induction also did not significantly increase the risk of negative infant outcomes, such as (0.0% versus 0.3%).
- The risk of having a baby weighing 4500 g or more was less in the induced group (3.2%) compared to expectant management group (14.8%) RR 0.21 (95% CI 0.11 to 0.39), and these babies had a lower incidence of foetal fractures (0.3%) compared to expectant management group (2.0%) RR 0.17 (95% CI 0.03 to 0.79).
What does current guidance say on this issue?
The 2008 NICE guideline on inducing labour states that in the absence of any other indications, induction of labour should not be carried out simply because a healthcare professional suspects a baby is large for gestational age. This is one of the recommendations currently being updated. Induction of labour is offered as for normal pregnancies at between 41 and 42 weeks’ gestation.
The 2008 NICE guideline on antenatal care for uncomplicated pregnancies (also currently being updated) adds that ultrasound to estimate the size of suspected large-for-gestational-age unborn babies should not be done in low-risk women.
What are the implications?
The authors of this analysis conclude that induction of labour at 38 weeks’ gestation or later is a “reasonable option” in women with a larger than normal baby. Healthcare professionals may wish to use these findings when advising pregnant women of their options.
A recent Cochrane review that analysed the same four trials came to more tentative conclusions, with the authors stating: “Although some parents and doctors may feel the evidence already justifies induction, others may justifiably disagree.” This caution is due to the limited information on rare negative outcomes.
This review does indicate that women who are induced are more likely to give birth a week earlier and less likely to have a heavier baby, without any difference in common negative outcomes.
Citation and Funding
Magro-Malosso ER, Saccone G, Chen M, et al. Induction of labour for suspected macrosomia at term in non-diabetic women: a systematic review and meta-analysis of randomized controlled trials. BJOG. 2017;124(3):414-21.
No financial support was received for this study.
Boulvain M, Irion O, Dowswell T, et al. Induction of labour at or near term for suspected fetal macrosomia. Cochrane Database Syst Rev 2016;(5):CD000938.
NHS Choices. Inducing labour. London: Department of Health; 2015.
NICE. Antenatal care for uncomplicated pregnancies. CG62. London: National Institute for Health and Care Excellence; 2008.
NICE. Inducing labour. CG70. London: National Institute for Health and Care Excellence; 2008.
Norwitz E. Induction of labour for fetal macrosomia: do we finally have an answer? BJOG 2016.
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