Risk in planned caesareans

Wednesday December 12 2007

“Planned caesareans linked to breathing difficulties” the headline in The Guardian states. The newspaper added that babies "born through a planned caesarean section are up to four times more likely to suffer from breathing problems”. The Times reported that caesareans were “on the rise in Britain and account for nearly 25 per cent of births”, and that this figure was "far above" the 10–15% rate recommended by the World Health Organisation.

The newspaper stories are based on a study of more than 34,000 births that showed a fourfold increase in respiratory problems in babies born at 37 weeks by planned caesarean compared with those born by vaginal delivery. At 39 weeks, the difference in the risk of developing breathing problems fell to two-fold. The researchers suggest that the hormonal and physical changes of labour are needed for a newborn baby's lungs to mature properly.

However, there are many reasons why women have a planned caesarean earlier. In particular one aim is to avoid labour during the caesarean, as this can lead to serious complications.

The researchers suggest that the results of their study “should be taken into consideration by women contemplating an elective caesarean section and by the obstetricians counselling them”.

Where did the story come from?

Dr Anne Kirkeby Hansen and colleagues from the Perinatal Epidemiology Research Unit, Aarhus University Hospital in Denmark, carried out the research. The study was supported by Aarhus University, Aarhus University Hospital, and the Aase and Einer Danielsens fund. It was published online in the peer-reviewed medical journal, British Medical Journal .

What kind of scientific study was this?

This was a prospective cohort study. The researchers used information from 34,458 babies born between 37 and 41 weeks of pregnancy during the period January 1 1998, to December 31 2006 at Aarhus University Hospital. The researchers were interested in the outcomes for low risk pregnancies only and they excluded all higher-risk pregnancies from the study, for example pregnancies where the mother had a small baby, diabetes or high blood pressure.

All the births were categorised as either vaginal, elective (planned) caesarean, emergency caesarean section and vacuum or forceps delivery, and the data were analysed according to which mode of delivery had been initially planned. This included 2,687 babies born by planned caesarean section and these were compared with more than 31,000 natural deliveries. The intended natural delivery category included women who intended to have a vaginal delivery but ended up with an emergency caesarean section.

A senior neonatal specialist examined all the babies after birth and confirmed any diagnosis of respiratory illness. All types of breathing problems that might occur in newborns – respiratory distress, fast breathing and increased blood pressure within the lungs (pulmonary hypertension) – was recorded as “neonatal respiratory morbidity”. Serious forms of these illnesses were defined as those that required three or more days of oxygen or ventilation. As some respiratory symptoms are known to be linked with vaginal delivery (such as pneumonia or blood poisoning, known as sepsis), any babies who developed these diseases were excluded from the analysis to see if the results were affected.

What were the results of the study?

A significantly increased risk of respiratory illnesses was found for infants delivered by planned caesarean section at 37 weeks’ of completed pregnancy compared with newborns from the intended for vaginal delivery group; the increased risk in respiratory illness was almost fourfold. At 38 weeks’ of completed pregnancy the chance of respiratory illness increased threefold and at 39 weeks’ gestation the chance was almost doubled.

The researchers adjusted the results to take into account minor differences between the groups that may have influenced the results, such as smoking, alcohol intake, and the number of previous pregnancies. The differences in risk of respiratory illness remained similar. The increased risk of serious respiratory illness reflected this pattern, but with larger differences in risk; for example, there was a fivefold increase in risk of serious respiratory illnesses at 37 weeks. When the researchers analysed the data and excluded the illnesses linked to vaginal delivery, there were similar results.

What interpretations did the researchers draw from these results?

The researchers conclude that compared with newborns delivered vaginally or by emergency caesarean sections, those delivered by elective caesarean section around term have an increased risk of overall and serious respiratory morbidity. The risk was highest in the babies born at the earlier weeks of pregnancy.

What does the NHS Knowledge Service make of this study?

This is a reliable study which further informs the debate about choice in pregnancy care. It has several strengths: data was collected over a long period, starting from before the women delivered their babies. This type of prospective design minimises the possibility of bias may influencing the results of the study. Such a large study also ensured that there were enough babies born in each week of pregnancy to analyse meaningfully for different respiratory illnesses. Some subgroups with serious illnesses contained very small numbers of infants for analysis and it is reassuring to note, for example, that only four infants born by elective caesarean at 37 weeks of pregnancy suffered serious illnesses requiring three days of oxygen or ventilation.

Although the study suggests that postponing an elective cesarean until 39 weeks gestation may reduce the risk of respiratory illness, as the authors also mention, there may be risks attached. It is likely that more women would start labour naturally before the booked date of their caesarean section. In this study about 25% of women who had planned to have a vaginal delivery went into labour before 39 weeks, suggesting that if women were booked for delivery by caesarean section at a later time about 25% of them could end up having an emergency caesarean instead.

Sir Muir Gray adds...

caesarean section is an operation and every operation has side effects. The pregnant woman considering a C-section needs to know the down side of the intervention, as well as the benefits. This seems to be another factor the woman needs to take into consideration.

Analysis by Bazian
Edited by NHS Choices