Obesity reduces pregnancy chances, study finds

Obesity cuts the chance of IVF working and increases the risk of premature birth and stillbirth, the largest US study into the issue has found.

The effect becomes more profound as weight increases, with the heaviest women having the lowest chance of success, according to data from almost 50,000 women.

The most obese women in the study had 35% less chance of falling pregnant and a 59% increased chance of giving birth to a very premature baby.

However, overweight women were also at risk, with a 13% lower chance of giving birth to a live baby and a 16% increased risk of premature birth.

Dr Barbara Luke, professor of obstetrics and gynaecology at Michigan State University in the US, presented her findings at the American Society for Reproductive Medicine (ASRM) conference in Atlanta.

She said: “The take-home message from this is that women need to reduce their weight before trying fertility treatment.

“Obesity increases the chance of having a premature baby and reduces the odds of pregnancy. And it increases the chances of stillbirth.

“Obesity is a state of inflammation and increasing obesity is not good.

“It is not conducive to conception and it is not conducive to pregnancy.”

The study included 28,094 women of normal weight, with a body mass index (BMI) of 18.5 to 24.9.

Another 11,710 women were overweight (BMI of 25 to 29.9), 5,187 were class I obese (BMI of 30 to 34.9), 2,276 were class II obese (BMI of 35 to 39.9) and 1,415 were class III obese (BMI over 40).

The results revealed that class I obese women had a 9% lower chance of falling pregnant, a 20% lower chance of a live birth and more than double the risk of stillbirth.

They were also 33% more likely to have a premature birth.

Among class II women, they were 28% less likely to fall pregnant, 26% less likely to have a live birth, had more than double the risk of stillbirth and a 38% increased risk of premature birth.

Class III women were 35% less likely to get pregnant, 25% less likely to have a live birth, had more than double the risk of stillbirth and were 34% more likely to give birth prematurely.

Stuart Lavery, consultant gynaecologist at the IVF unit at Hammersmith Hospital in London, said the results offered “concrete evidence” of the link with obesity.

“It reaffirms the issue that obesity really does impact on the chance of fertility treatment being successful,” he said.

“It does so significantly and convincingly.”

Most public UK hospitals like female patients seeking IVF to have a BMI under 30, he said.

In 2007, the British Fertility Society said women with a BMI over 35 should not normally receive treatment until they had lost weight.

Tam Fry, from the National Obesity Forum, said: “This study underlines the fact that if you are thinking about having children, you should start thinking about losing weight at least six months before you conceive.

“Too many women are not doing that – and many are putting on weight during pregnancy.

“Women need to understand that obesity can not only affect themselves – it can affect their child.

“If the mother is obese, their child is three times more likely to be obese; and if the father is obese too the child is eight times more likely to be obese.”