Risks of caesarean sections

Wednesday October 31 2007

Caesareans put both mothers and babies at increased risk of death, reported The Independent and other newspapers. Women are at “twice the risk of illness or death compared to a vaginal birth”, the newspaper stated. They say that a study has found that babies born by caesarean section “had a 70 per cent higher risk of dying before discharge from hospital”.

Many of the newspapers present this story as relevant to women who are considered “too posh to push” and would opt for a caesarean by choice. However, the vast majority of caesareans are conducted for medical reasons, where the risk to the mother and infant is considered to be greater if a caesarean is not performed. Overall, the study on which the reports were based found that the risk for death at birth in babies born by caesarean was no different from those born naturally. In fact, caesarean has “a large protective effect on foetal death” for breech babies, the authors concluded.

Where did the story come from?

The study was carried out by Jose Villar and various colleagues from hospitals and institutes in a variety of countries including Oxford, England; Rosario, Argentina; and Lima, Peru. Funding was provided by United Nations Development Programme/United Nations Population Fund/World Health Organisation/World Bank Special Programme of Research, Development and Research Training in Human Reproduction, Department of Reproductive Health and Research and the US Agency for International Development. It was published in the peer-reviewed British Medical Journal.

What kind of scientific study was this?

This is a cohort study conducted as part of the 2005 World Health Organisation (WHO) global survey into maternal and perinatal health (health around the time of birth).

This study was carried out in 123 health care facilities within 24 areas of eight Latin American countries. The types of hospital differed in the resources they had available; some were public, some private, others belonging to the social security system. The researchers collected data on all women who delivered babies at the health centres over a two or three month period between September 2004 and March 2005. Information was collected on potential risks prior to conception, health during pregnancy, type of delivery, events prior to hospital discharge and demographic details. If a caesarean was performed, they noted whether it was elective (planned before labour onset), or took place during labour for any reason, but they excluded caesareans that were performed as an emergency outside of labour (e.g. for serious vaginal bleeding). They also excluded women who had multiple births (twins, etc).

The researchers monitored the babies and recorded events such as admission to a neonatal intensive care unit or death. Maternal events such as blood transfusion, admission to intensive care, stay in hospital and death were also recorded. The researchers compared events for both the baby and the mother between natural birth and the two caesarean indications examined. 94,307 births were analysed, 66% of which were natural births and 34% were caesarean deliveries.

What were the results of the study?

The researchers found that when they adjusted for other factors such as the number of previous pregnancies, medical problems during pregnancy, high blood pressure and vaginal bleeding the risk of severe illness or death in mothers who had a caesarean was double that of women who had a natural birth. Caesarean mothers also had a five times greater risk of needing antibiotic treatment. When they investigated other perinatal events, the researchers also found an increase in the risk of intensive care admission, need for blood transfusion and hysterectomy.

When they compared the characteristics of women who had caesareans with those who had natural births, they found that a higher proportion of women with risk factors or complications in previous or current pregnancy had elective caesareans. The most common indications for an elective caesarean were a previous caesarean, breech baby, pre-eclampsia, and other maternal complications.

When considering the babies, without making adjustments for other factors that may have been responsible for the difference between the groups (e.g. foetal presentation, gestational age, medical conditions, type of facility etc), they found there to be no difference between the groups in the numbers of babies who died during birth. They found that elective caesarean increased the risk of illness and death that occurred up to the time the mother was discharged from hospital.

When the researchers adjusted for important factors (mother’s age, gestational age, previous stillbirth, vaginal bleeding or other medical conditions, country, whether labour was induced) they found that elective caesarean reduced the risk of death compared with vaginal delivery, particularly when the baby was a breech birth. This reduction was still very significant for breech babies who required caesarean during labour (i.e. were not  “elective caesareans”). There was no difference in risk of death between caesarean during labour and vaginal birth for babies born head first.

The researchers also found that for babies born head first, caesarean delivery was linked to an approximately doubled risk of stay in intensive care of seven days or more, and 70–90% increased (i.e. less than doubled) risk of death up to time of hospital discharge. 194 out of 27,671 (0.7%) babies who were delivered by caesarean (elective or not) died before hospital discharge compared to 231 out of 61,299 (0.38%) delivered vaginally. For breech presentations, there was no difference in these outcomes between caesarean and vaginal deliveries.

What interpretations did the researchers draw from these results?

The researchers conclude that caesarean delivery overall increases the risk of death and illness in the mother and the baby who is born by caesarean section compared with vaginal delivery, but that caesarean is protective for babies who are breech during labour.

What does the NHS Knowledge Service make of this study?

This study provides a large amount of data about the outcomes of a large number of births in Latin America. However, there are number of important points that must be considered when drawing any conclusions from these results:

  • Caesarean sections are often required for a number of maternal and infant reasons. By their very nature (i.e. they are used when there are complications) they are likely to be associated with an increased risk of problems. Although they have adjusted for some of these complications in their calculations, many others may not have been considered. An increased risk of antibiotic use is also not surprising as this is an invasive operation and antibiotics are often required after many operations. Having any operation and an anaesthetic is always associated with some small risk, therefore, the fact that these women would have some increased risk of complications compared with women who did not need these interventions is not surprising. 
  • It is not possible to compare the outcomes in the mothers or babies of those women who it was considered to be safer for their health to have a caesarean, but who had a vaginal delivery (e.g. perhaps due to lack of resources in their healthcare facility). A much greater risk of death to both mother and child would probably be seen if the women in this group who needed a caesarean section had delivered babies vaginally instead. 
  • The actual risk of a negative outcome to the mother or baby is very small. Reporting in the news that babies born by caesarean could be at “70% risk of death” could be interpreted in different ways by members of the public. To put it in perspective, there were a total of 435 deaths during birth in this population of over 94,000 women. As the results of this study found, the overall risk of death for the baby at birth was not increased by caesarean and caesarean sections were clearly protective for breech presentations. 
  • The issue of opting for caesarean section when there is no maternal or foetal indication has been raised by some of the newspapers in their headlines of risk to women ”too posh to push.” This issue has not been considered by this study, which has looked at all elective caesareans and not specifically the group who choose it for personal reasons. The vast majority of caesareans are conducted for medical reasons where the risk to the mother and infant is considered greater if a caesarean is not performed.

Analysis by Bazian
Edited by NHS Choices