UK scientists studying women with a history of unexplained recurrent miscarriage found that the risk of a further miscarriage for obese women was significantly higher than that of normal weight women. They recommended counselling should be given to pregnant women who are obese to help them understand the benefit that weight loss may have on pregnancy outcome, but other experts urge caution because there are also risks associated with losing weight during pregnancy.

The study was the work of a team from London's St Mary's Hospital who presented their findings at the Royal College of Obstetrics and Gynaecology's 7th international scientific meeting in Montreal last week. An abstract is also published in a special September 2008 issue of BJOG.

The links between miscarriage and maternal obesity have been well studied and established, but this is the first study to look at recurrent miscarriages for which there is no explanation, said the authors.

For the study, clinical nurse specialist at the hospital, Winnie Lo, and colleagues, examined 398 women who had been attending the hospital with their partners for unexplained miscarriages between 1996 and 2006. They then followed them on their next pregnancy and also put them into four groups depending on their Body Mass Index (BMI). When they analysed the data they adjusted the results for potential confounders like age, a well know risk factor for miscarriage.

The results showed that:
  • 1 per cent of the women were underweight (BMI under 18.50).

  • 49 per cent were of normal weight (BMI 18.50 to 24.99).

  • 34 per cent were overweight (BMI 25.00 to 29.99).

  • 16 per cent were obese (BMI of 30.00 and over).

  • 0.5 per cent of the women who miscarried in their next pregnancy were underweight.

  • 44.9 per cent of the women who miscarried in their next pregnancy were of normal weight.

  • 33.3 per cent of the women who miscarried in their next pregnancy were obese.

  • Compared to women of normal weight, obese women had a significantly higher risk of miscarriage (odds ratio 2.3).

  • The figures for overweight and underweight women did not show a signficantly increased risk of miscarriage.
The authors concluded that:

"This study demonstrated that women with unexplained RM [recurrent miscarriage] who are obese (BMI greater than or equal to 30 kg/m2) have a significantly increased risk of miscarriage in future pregnancies compared to those with a normal BMI."

"These women should be counselled regarding the significant beneficial effect on pregnancy outcome to be gained by weight loss," they added.

An obesity specialist told the BBC that it could be dangerous to lose weight while pregnant, suggesting the advice of this study should be treated with caution. Dr Nick Finer, an endocrinologist with an interest in obesity who is based at Addenbrooke's Hospital near Cambridge, called the findings "unsurprising".

Fisher said scientists already knew that increasing BMI is linked to reduced fertility, increased risk of fetal malformation and other adverse pregnancy outcomes. While it was not clear why obesity should cause these problems, he suggested perhaps it had something to do with increased inflammation.

Fisher said while there may be good reasons for obese women to lose weight before getting pregnant, doing so once pregnancy is established could cause problems.

"Effect of body mass index on pregnancy outcome in women with unexplained recurrent miscarriage."
Lo, W; Rai, R; Hameed, A; Marikinti, K; Al-Ghamdi, A; Regan, L.
Abstract number FC6.06
BJOGVolume 115 Issue s1, p 32-66 (September 2008)
DOI:10.1111/j.1471-0528.2008.01888.x
Presented to the Royal College of Obstetrics and Gynaecology's 7th international scientific meeting in Montreal, 17 - 20 September, 2008

Click here for BJOG.

Source: Conference Abstract, BBC News.

Written by: Catharine Paddock, PhD