予定帝王切開(elective Caesarean section)は、自然分娩や緊急帝王切開に比べて４倍も新生児の呼吸障害をきたすと、デンマークからの報告。分娩中のホルモンや生理学的な変化が児の肺の成熟に役立っている可能性がある。
Last Updated: Wednesday, 12 December 2007, 01:17 GMT
Caesareans 'may harm lung growth'
Image of a baby in an incubator
Labour may help mature the lungs
Babies born by elective Caesarean section are much more likely to develop breathing problems, a Danish study examining 34,000 deliveries suggests.
Researchers found they were up to four times more likely to have respiratory problems than those born naturally, or by emergency Caesarean section.
The babies may miss out on hormonal and physiological changes during labour which help mature the lungs, they say.
The University of Aarhus study features in the British Medical Journal.
Almost a quarter of UK births are now estimated to be Caesarean sections - far above the 10% to 15% rate recommended by the World Health Organization.
A lot of woman are completely unaware of the fact that a planned Caesarean section can negatively impact on their baby
Dr Maggie Blott
More than half of these were emergency Caesareans, but despite this experts have been calling for measures to reduce numbers of elective Caesareans, warning it is a major operation.
A recent Oxford University study found that women could be four times more likely to die in childbirth if they opted for a Caesarean instead of natural birth.
The Danish team examined data on over 34,000 deliveries, adjusting to take account of factors such as the mother's age, weight, and whether she smoked or drank alcohol during pregnancy
They found that babies born by elective Caesarean section had an increased risk of general respiratory problems.
The risk was higher the earlier the Caesarean was performed.
A nearly fourfold increased risk was found at 37 weeks gestation, a threefold increase in risk at 38 weeks gestation, and a doubling of risk in infants delivered at 39 weeks gestation.
For example, at 37 weeks, one in 10 babies delivered by elective Caesarean section developed respiratory problems, compared with 2.8% of infants delivered naturally or by emergency Caesarean section.
At 38 weeks, the proportion was 1.7% compared with 5.1% and at 39 weeks, 1.1% compared with 2.1%.
The risks of serious respiratory problems showed the same pattern.
The researchers conclude that significantly fewer babies would develop breathing problems if elective Caesareans were put off until 39 weeks gestation.
They said: "It is plausible that hormonal and physiological changes associated with labour are necessary for lung maturation in neonates and that these changes may not occur in infants delivered by elective Caesarean sections."
Dr Maggie Blott, a consultant obstetrician at King's College Hospital, London, said obstetricians in the UK were advised not to carry out elective Caesareans before 39 weeks.
She said part of the problem might be that doctors had to switch support lines to the baby very quickly during a Caesarean, and it was possible that lung fluid is not drained away as well as it should be.
She said: "Some babies do develop transient breathing problems, they usually recover from them, but occasionally a baby can be very sick indeed.
"A lot of woman are completely unaware of the fact that a planned Caesarean section can negatively impact on their baby.
"Any research which reinforces the fact that Caesareans are not necessarily in the best interests of the baby is welcome."
Mervi Jokinen, of the Royal College of Midwives, said Caesarean section rates were too high in the UK.
She said it was a major operation, which had health implications for the mother, as well as the baby.
"The decision to opt for a Caesarean section should not be taken lightly and should be based on good medical grounds," she said.
BMJ, doi:10.1136/bmj.39405.539282.BE (published 11 December 2007)
Risk of respiratory morbidity in term infants delivered by elective caesarean section: cohort study
Anne Kirkeby Hansen, research fellow1, Kirsten Wisborg, staff specialist2, Niels Uldbjerg, professor3, Tine Brink Henriksen, associate professor2
1 Perinatal Epidemiology Research Unit, Aarhus University Hospital, Brendstrupgaardsvej 100, Skejby, 8200 Aarhus N, Denmark, 2 Department of Paediatrics, Aarhus University Hospital, 3 Department of Obstetrics and Gynaecology, Aarhus University Hospital
Correspondence to: A K Hansen AKH@svf.au.dk
Objective To investigate the association between elective caesarean sections and neonatal respiratory morbidity and the importance of timing of elective caesarean sections.
Design Cohort study with prospectively collected data from the Aarhus birth cohort, Denmark.
Setting Obstetric department and neonatal department of a university hospital in Denmark.
Participants All liveborn babies without malformations, with gestational ages between 37 and 41 weeks, and delivered between 1 January 1998 and 31 December 2006 (34 458 babies).
Main outcome measures Respiratory morbidity (transitory tachypnoea of the newborn, respiratory distress syndrome, persistent pulmonary hypertension of the newborn) and serious respiratory morbidity (oxygen therapy for more than two days, nasal continuous positive airway pressure, or need for mechanical ventilation).
Results 2687 infants were delivered by elective caesarean section. Compared with newborns intended for vaginal delivery, an increased risk of respiratory morbidity was found for infants delivered by elective caesarean section at 37 weeks’ gestation (odds ratio 3.9, 95% confidence interval 2.4 to 6.5), 38 weeks’ gestation (3.0, 2.1 to 4.3), and 39 weeks’ gestation (1.9, 1.2 to 3.0). The increased risks of serious respiratory morbidity showed the same pattern but with higher odds ratios: a fivefold increase was found at 37 weeks (5.0, 1.6 to16.0). These results remained essentially unchanged after exclusion of pregnancies complicated by diabetes, pre-eclampsia, and intrauterine growth retardation, or by breech presentation.
Conclusion 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 relative risk increased with decreasing gestational age.
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