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Induction of labour at or near the end of pregnancy for babies suspected of being very large (macrosomia)

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Link to most recent Cochrane Review Update

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Link to most recent Cochrane Review Update

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INCLUDES LINKS FOR OTHER LANGUAGES

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What is the issue?

Babies who are very large (or macrosomic, weighing over 4000 g when born) can have difficult and occasionally traumatic births. One suggestion to try to reduce this has been to induce labour early, before the baby grows too big. The estimation of the baby's weight is difficult before birth and not very accurate. Clinical estimations are based on feeling the uterus and measuring the height of the fundus of the uterus. Both are subject to considerable variation. Ultrasound scanning is also not accurate, so suspected large babies may not be confirmed at delivery. This may worry parents.

Why is this important?

If undertaken too early, of labour can lead to babies being born prematurely and with immature organs.

What evidence did we find?

We found four trials that assessed of labour at 37 to 40 weeks for women when it was suspected that their baby was large. A total of 1190 pregnant, non-diabetic women were involved. We searched for evidence on 31 October 2015. The studies were of moderate or good quality although it was not possible to the women and staff providing care to which group women had been assigned. This may have introduced .

What does this mean?

The number of births where the baby's shoulder became stuck (shoulder dystocia) or a bone was fractured (usually the clavicle, which heals well without consequences) were reduced in the of labour group. The evidence was assessed as moderate quality for shoulder dystocia and high quality for fracture. No clear differences between groups were reported for damage to the network of nerves that send signals from the spine to the shoulder, arm and hand (brachial plexus injury) of the baby (low-quality evidence due to very few events occurring) or signs of not enough oxygen during birth. A policy of labour reduced the average birthweight of babies by 178 g. The trials did not show any differences in the number of women who had caesarean sections or instrumental births. There is limited evidence that more women in the of labour group had severe damage to the perineum. We conclude that there appear to be benefits, but there may also be some disadvantages of of labour shortly before term. The option of having an should be discussed with parents when their baby is suspected to be extra large.

Although some parents and doctors may feel the existing evidence is sufficient to justify inducing labour, others may disagree. Further high-quality studies are needed in order to find out what is the best time to induce labour towards the end of pregnancy, and how to improve the accuracy in diagnosing macrosomia.

A visual summary of some of the results from this can be found here (screen view version) and (printable version here).

Induction of labour for suspected fetal macrosomia has not been shown to alter the of brachial plexus injury, but the of the included studies to show a difference for such a rare event is limited. Also antenatal estimates of fetal weight are often inaccurate so many women may be worried unnecessarily, and many inductions may not be needed. Nevertheless, of labour for suspected fetal macrosomia results in a lower birthweight, and fewer birth fractures and shoulder dystocia. The unexpected observation in the group of increased perineal damage, and the plausible, but of uncertain significance, observation of increased use of phototherapy, both in the largest , should also be kept in mind.

Findings from trials included in the suggest that to prevent one fracture it would be necessary to induce labour in 60 women. Since of labour does not appear to alter the rate of caesarean delivery or instrumental delivery, it is likely to be popular with many women. In settings where obstetricians can be reasonably confident about their scan assessment of fetal weight, the advantages and disadvantages of at or near term for fetuses suspected of being macrosomic should be discussed with parents.

Although some parents and doctors may feel the evidence already justifies , others may justifiably disagree. Further trials of shortly before term for suspected fetal macrosomia are needed. Such trials should concentrate on refining the optimum gestation of , and improving the accuracy of the diagnosis of macrosomia.

Read the full abstract...

Women with a suspected large-for-dates fetus or a fetus with suspected macrosomia (birthweight greater than 4000 g) are at of operative birth or caesarean section. The baby is also at increased of shoulder dystocia and , in particular fractures and brachial plexus injury. Induction of labour may reduce these risks by decreasing the birthweight, but may also lead to longer labours and an increased of caesarean section.

To assess the effects of a policy of labour at or shortly before term (37 to 40 weeks) for suspected fetal macrosomia on the way of giving birth and maternal or perinatal .

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 January 2016), contacted authors and searched reference lists of retrieved studies.

Randomised trials of of labour for suspected fetal macrosomia.

Data collection and analysis:

Review authors independently assessed trials for inclusion and of , extracted and checked them for accuracy. We contacted authors for additional information. For key outcomes the quality of the evidence was assessed using the GRADE approach.

We included four trials, involving 1190 women. It was not possible to women and staff to the intervention, but for other 'Risk of ' domains these studies were assessed as being at low or unclear of .

Compared to expectant management, there was no clear effect of of labour for suspected macrosomia on the of ( () 0.91, 95% confidence interval () 0.76 to 1.09; 1190 women; four trials, moderate-quality evidence) or instrumental delivery ( 0.86, 95% 0.65 to 1.13; 1190 women; four trials, low-quality evidence). Shoulder dystocia ( 0.60, 95% 0.37 to 0.98; 1190 women; four trials, moderate-quality evidence), and fracture (any) ( 0.20, 95% 0.05 to 0.79; 1190 women; four studies, high-quality evidence) were reduced in the of labour group. There were no clear differences between groups for brachial plexus injury (two events were reported in the control group in one , low-quality evidence). There was no strong evidence of any difference between groups for measures of neonatal asphyxia; low five-minute infant Apgar scores (less than seven) or low arterial cord blood pH ( 1.51, 95% 0.25 to 9.02; 858 infants; two trials, low-quality evidence; and, 1.01, 95% 0.46 to 2.22; 818 infants; one , moderate-quality evidence, respectively).

Mean birthweight was lower in the group, but there was considerable heterogeneity between studies for this ( mean difference () -178.03 g, 95% -315.26 to -40.81; 1190 infants; four studies; I ² = 89%). In one with for 818 women, third- and fourth-degree perineal tears were increased in the group ( 3.70, 95% 1.04 to 13.17).

For outcomes assessed using GRADE, we based our downgrading decisions on high of from lack of and imprecision of effect estimates.

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Induction of labour at or near the end of pregnancy for babies suspected of being very large (macrosomia)

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What is the issue? Babies who are very large (or macrosomic, weighing over 4000 g when born) can have difficult and occasionally traumatic births. One suggestion to try to reduce this has been to induce labour early, before the baby grows too big. The estimation of the baby's weight is difficult before birth and not very accurate.

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Your doctor will take to you about waiting for labour to start naturally (called 'expectant management') compared to having your labour started early (induction of labour).

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What are the pros and cons of induction vs expectant management?

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What are the pros and cons of induction vs expectant management?

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The evidence suggests that the risk of emergency Caesarean birth, nerve injury to baby and perinatal death are small and the same for both options

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Induction of labour is a medical intervention. Consider the impact of this on your birth experience and talk to your doctor or midwife about how this might impact your choices.

Consider the impact of the gestation that induction might occur at. There is evidence of longer term impact on childhood development with early induction of labour.

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You have been signposted here to help you understand :

- What is 'suspected macrosomia' or a 'big baby'
- What are risks?
- What are your options for birth?
- What are the advantages and disadvantages of induction of labour compared to waiting for labour to start naturally ('expectant management')

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The most quoted concern is the risk of and consequences of shoulder dystocia.

This is when your baby's head is born but there is a delay in your baby's body being born.

Extra help is needed to deliver your baby's shoulders and in the majority of cases baby's are then born quickly and safely.

Shoulder dystocia is more likely in babies over 4.5kg nevertheless the majority of babies are born without any difficulty.

Half of all instances of shoulder dystocia happen in babies LESS than 4kg.

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Shoulder dystocia patient information leaflet | RCOG

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This information is for you if you wish to know about shoulder dystocia. You may also find it helpful if the birth of your baby was complicated by shoulder dystocia. It may be helpful if you are a partner, relative or friend of someone who has been in this situation.

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There is no standard definition.
The National Institute for Health and Care Excellence (NICE) guidelines define it as growth >95th centile (at least 95% of babies are smaller) on the customised growth chart or estimated weight of >4000g on an ultrasound.

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Ultrasound estimates of fetal weight can over or underestimate the actual birthweight of babies by 15-20%.

So your baby's birth weight may be up to 20% bigger or 20% smaller than predicted.

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Click here for more general information on the process of induction of labour

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Click here for more general information on the process of induction of labour

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There is currently no evidence that a caesarean birth improves outcomes for mothers or babies if the only concern is that the baby’s weight is estimated to be ≥4kg on USS. It is associated with a significant number of risks to mother, baby and impact on future births and it is not recommended.

National guidance currently recommends offering caesarean section if estimated weight is >5kg in women without diabetes and >4.5kg in women with diabetes.  This is based on expert opinion rather than any studies.

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Published: 4 August 2022

This information is for you if you are considering a planned (elective) caesarean birth for your baby. It may also be helpful if you are a partner, relative or friend of someone who is considering a caesarean birth.

This information is not for you if you have already been offered a caesarean birth because of specific reasons in your pregnancy, as the benefits and risks will be different. If you are in that situation, your healthcare professional will discuss your options for birth with you.

If you have had a caesarean birth in the past, please see the RCOG patient information Birth options after previous caesarean section.

The information here aims to help you better understand your pregnancy and your options for planning the birth of your baby. Your healthcare team is there to support you in making your decision. They can help by discussing your preferences, providing you with further information and answering your questions.

The figures quoted in this information are based on the best available research, which is limited. When considering the benefits and risks of your different options, it is important to bear in mind that we have to rely on studies of variable quality, including some that compare planned caesarean births for all reasons (including caesarean births for women who have medical factors) with vaginal births, or emergency caesarean births with vaginal births.

Within this leaflet we may use the terms 'woman' and 'women'. However, we know that it is not only people who identify as women who may want to access this leaflet for information about their choices around birth. Your care should be appropriate, inclusive and sensitive to your needs whatever your gender identity.

A glossary of medical terms is available on the RCOG website on A-Z of medical terms.

Key points

Most women in the UK recover well and have healthy babies whether they have a vaginal or a caesarean birth.

A planned caesarean birth is a surgical procedure with risks and these should be balanced with the risks associated with a planned vaginal birth.

Every woman is different, and your individual needs and preferences will play the most important role in planning the birth of your baby.

If you are considering a caesarean birth or have any questions or anxieties regarding birth, you should tell your healthcare professional as soon as possible.

If, having considered the benefits and risks of your different options for birth, you decide that a planned caesarean is how you would like your baby to be born, your healthcare team should support this choice.

Further information

NHS Choices - Caesarean section: www.nhs.uk/Conditions/Caesarean-section/Pages/Introduction.aspx

NICE guideline on caesarean section: www.nice.org.uk/guidance/cg132/informationforpublic

Royal College of Obstetricians and Gynaecologists - Planned Caesarean Birth (Consent Advice No. 14)

Sources and acknowledgements

This information has been developed by the following organisations: Birthrights, Birth Trauma Association, Caesarean Birth, National Birth Trust, RCOG Patient Information Committee, Royal College of Midwives and the RCOG Women's Network.

It is based on NICE guideline [NG192] Caesarean birth published in 2021, with supplemented data accessed from the NHS Digital Maternity Services dashboard and Rashid TG et al.; on behalf of the British Association of Urological Surgeons, Caesarean bladder and ureteric injuries in the UK (Journal of Clinical Urology 2014).

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Considering a caesarean birth patient information leaflet

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This information is for you if you are considering a planned (elective) caesarean birth for your baby. It may also be helpful if you are a partner, relative or friend of someone who is considering a caesarean birth.

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There is currently no evidence that the centile on which a baby’s estimated weight falls is associated with adverse outcomes (e.g., delay in labour, emergency caesarean birth, instrumental birth, shoulder dystocia (SD), perineal tears extending to the anal sphincter, or post-partum haemorrhage) unless the baby is estimated to weigh ≥4kg.

Estimated Fetal Weight of >4 or 4.5kg (called 'suspected macrosomia') is a poor predictor of shoulder dystocia but is associated with a significant incidence of obstetric intervention independent of actual fetal weight.