Childbirth risks not the same for all obese women

Obesity raises the chances of complications and medical interventions in childbirth. But a new study by Oxford University shows the risks are not the same for all obese women.

For otherwise healthy women, the increase in risk with obesity may not be as great as previously suspected.

'The increased risk was fairly modest for obese women who did not have conditions such as high blood pressure, diabetes or a previous caesarean section, and the risks were quite low if the woman had given birth previously,' says lead researcher Dr Jennifer Hollowell of the National Perinatal Epidemiology Unit at Oxford University.

'It is important to appreciate that we are not saying that obesity isn't important or that obesity doesn't increase a woman's risks during pregnancy,' she adds. 'We found that around half of very obese women giving birth in obstetric units have medical problems or pregnancy complications when admitted. But our study focused on women who were obese but otherwise healthy when they went into labour, and some of them had much lower risks than might have been expected.'

The Oxford University researchers point out that, among healthy women with a straightforward pregnancy, childbirth risks are influenced more by whether someone is a first-time mum than whether they are obese.

They found that the chances of first-time mums of normal weight having medical interventions or complications during childbirth are greater than for 'very obese' but otherwise healthy women having a second or subsequent child. The findings are published in the British Journal of Obstetrics and Gynaecology.

Dr Hollowell comments: 'This finding does highlight a possible anomaly in the guidance given to women on where to give birth.'

First-time mothers with low-risk pregnancies can plan to have their child in hospital, at home, in a free-standing midwife-led unit or an alongside midwifery unit connected to a hospital – according to what is available where they are.

However, current guidelines suggest all women with a body mass index (BMI) over 35 should be advised to have the birth in an obstetric unit to reduce risk.

Guidelines on assessing risks for women in planning births take no account of whether a woman is having their first child or has already had children.

'We think that the guidelines might need to be reviewed to take account of this more nuanced understanding of the effect of obesity,' says Dr Hollowell. 'We think it's worth considering whether it might be safe to allow some healthy obese women having a second baby the option of a birth in an alongside midwifery unit where obstetric and neonatal care is available on site if needed.'

The researchers investigated the influence of BMI on the chances of healthy women having any type of complication during labour and childbirth that would need hospital care – either in an obstetric unit for the mother or a neonatal unit for the baby.