Carrying excess weight is already known to affect fertility
Women who have had a miscarriage could be at greater risk of miscarrying again if they are obese, research suggests.
A team from London's St Mary's Hospital followed the progress of 696 women whose miscarriages were classed as "unexplained" by a specialist clinic.
The team told a conference in Canada the risk of a further miscarriage was raised by 73% if the woman was obese.
However, an obesity specialist said it was potentially dangerous to try to lose weight when already pregnant.
Although the links between being obese and having problems conceiving and complications during pregnancy are well known, this study claims to be the first to look specifically at "recurrent" miscarriage, for which there is often no obvious cause.
Of the 696 women whose cases were followed, more than half were of "normal" weight, 30% were overweight, and 15% were obese, meaning they had a body mass index (BMI) of 30 or above.
The older the woman, the higher chance she had of having another miscarriage, but, when the figures were adjusted to account for this, obesity emerged as another possible factor.
While there was no difference in the miscarriage rates for overweight, normal and underweight women, the risk of further miscarriage increased sharply for obese women.
Winnie Lo, a clinical nurse specialist at St Mary's, who presented the research at the Royal College of Obstetrics and Gynaecology's international meeting in Montreal, said: "This is the first study to look directly at the link between BMI and recurrent miscarriage.
"It shows that obese women who experience recurrent miscarriage are at greater risk of subsequent pregnancy loss.
"All women with recurrent miscarriage should be weighed at their first consultation.
"Those who are found to be obese should be counselled regarding the benefits of weight loss."
Dr Nick Finer, an endocrinologist with an interest in obesity from Addenbrooke's Hospital near Cambridge, said that the findings were "unsurprising".
"We already know that the chances of fertility are less with increasing BMI, the risks of foetal malformation increase, alongside the risks of other adverse pregnancy outcomes."
He said that, while the reason why obesity might cause such problems was not clear, it was possible that it increased inflammation, harming the chances of a successful pregnancy.
However, he warned that crash diets during pregnancy would never be recommended as a means of increasing the chances of success.
"There are good reasons to try to lose weight before getting pregnant, but it is recommended that women do not try to do this once pregnancy is established, as it could cause problems."