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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

Routine data from English hospitals show that general surgery during pregnancy, such as removing the appendix or gallbladder, does not commonly harm mother or baby. This suggests that surgery in pregnant women is generally safe, but that mothers could be provided with more specific estimates of the risks.

This large observational study assessed the “real world” outcomes of nearly 6.5 million pregnancies at hospitals in England over a 10-year period.

Women who had surgery during pregnancy for a condition unrelated to pregnancy were slightly more likely to experience miscarriage, preterm or caesarean delivery or a long stay in hospital. Babies were more also slightly more likely to be low birthweight or stillborn.

However, the actual risks of negative outcomes were small. For example, 287 pregnant women would need to have surgery for one to experience a stillbirth and it was not possible to balance the benefits of their surgery against this as procedures were so varied.

There isn’t any guidance on surgery in pregnancy in the UK, so these findings may be useful when discussing surgery and the associated risks with pregnant women.

Why was this study needed?

An estimated 1-2% of women have surgery during pregnancy for a condition unrelated to their pregnancy, such as having their appendix or a potentially cancerous tumour removed.

Surgery during pregnancy might be risky for both the mother and infant. A systematic review in 2005 found that among women who had surgery during pregnancy, 8.2% had premature delivery, 5.8% experienced miscarriage (10.5% if surgery took place in the first trimester) and 2% had a stillbirth.

However, this previous review did not compare these rates with those in women who did not have surgery, and many of the studies were not conducted in the UK. Trials are unlikely to be conducted in this area.

Therefore, more up-to-date observational UK data was required to help women decide whether or not to delay surgery until after pregnancy, if this is possible.

What did this study do?

This observational study compared birth outcomes in women who had surgery during pregnancy and women who did not have surgery during pregnancy.

Hospital Episode Statistics (HES) data were searched to identify all women in England aged 15 to 49 years who were pregnant between 2002 and 2012. HES are a comprehensive set of records on all hospital care in England, so is a reliable source of information for this retrospective cohort or registry study.

Diagnosis codes were used to identify whether women had surgery during pregnancy and whether they had one of the following adverse mother or baby outcomes: miscarriage, preterm delivery, caesarean section, death, long stay in hospital, low birthweight baby or stillbirth.

The study is large and by using routinely collected data is an example of one of the best ways to collect data on rare adverse events. As an observational study, it cannot confirm for sure if surgery itself caused a poor outcome or whether other factors due to the underlying condition itself were at play. However it improves available knowledge on the risks.

What did it find?

  • Among the 6,486,280 pregnancies identified, 47,628 (0.7%) had surgery. Abdominal surgery (such as removing the appendix or gallbladder) was the most common type of surgery.
  • Pregnant women who had surgery had an increased risk of adverse birth outcomes compared with those who did not have surgery. Risks ranged from being a tenth more likely for miscarriage (relative risk [RR] 1.13, 95% confidence interval [CI] 1.09 to 1.17) to over four times more likely for maternal death (RR 4.72, 95% CI 2.61 to 8.52). However, the baseline risk of maternal death was very low, at only 12 deaths amongst the 47,000 women who had surgery.
  • A total of 25 pregnant women would need to have surgery for one additional woman to have a caesarean section who would otherwise not have had one if she had not had surgery.
  • A total of 7692 pregnant women would need to have surgery for one additional maternal death; 287 for one additional stillbirth; 50 for one additional long inpatient stay; 39 for one additional low birthweight baby; and 31 for one additional preterm delivery.

What does current guidance say on this issue?

There is UK guidance advising that pregnancy status is checked for prior to general surgery, but UK guidance does not specify when it is safe to carry out surgery in pregnant women for conditions unrelated to the pregnancy.

The American College of Obstetricians and Gynaecologists provided a Committee Opinion on surgery unrelated to the pregnancy in 2015. They recommend that if possible, non-urgent surgery that cannot wait until after the pregnancy should be performed in the second trimester.

The college also provides some reassurance that anaesthetics in current use have not been shown to have any negative effect on the growth or development of the foetus.

What are the implications?

This large study used up-to-date routinely collected UK data to show that surgery in pregnant women is generally safe for the mother and baby. One result of this study is that the extent of any increased risk is now clearer. The findings therefore, may help guide conversations between healthcare professionals and pregnant women about the risks of surgery.

This could allow a discussion on the timing of surgery in pregnancy or whether surgery could be even be postponed till after birth, for example, if this was possible.

Citation and Funding

Aylin P, Bennett P, Bottle A, et al. Estimating the risk of adverse birth outcomes in pregnant women undergoing non-obstetric surgery using routinely collected NHS data: an observational study. Health Serv Deliv Res. 2016;4(29).

This project was funded by the National Institute for Health Research Health Services and Delivery Research programme (project number 12/209/59).


ACOG. Nonobstetric surgery during pregnancy. Committee Opinion Number 474. Washington: American College of Obstetricians and Gynaecologists; 2015.

Cohen-Kerem R, Railton C, Oren D, et al. Pregnancy outcome following non-obstetric surgical intervention. Am J Surg. 2005;190(3):467-73.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre

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