According to research, it might be futile to advise obese women that they lose weight before considering fertility treatments.

Very overweight women struggling to conceive are often told by NHS bosses to slim down because carrying extra body fat is linked with decreased fertility.

Experts now believe losing weight won’t make any difference according to the first ever randomised controlled trial.

Penn State University scientists compared fertility rates among 300 obese women trying to conceive.

Half of the participants were placed on a 16 week weight loss/exercise program and allowed to consume just 1,200 calories per day. The results were compared to a group that was told to eat as usual. 

There was no significant difference in the success rates of pregnancy between the two groups after three treatment cycles — even though the restricted calorie group lost 1st 1lb (7kg) on average.

Richard Legro who was the lead of the study said the results did not show enough evidence to suggest quick fat loss for conceiving.

However, he recognized that the fertility gains could be long term.

This graph compares the percentage of obese women who were on a 16-week weight loss program (left) and those who did not. Scientists concluded that there wasn’t a significant difference between both the groups. 

On average, even women who lost weight still weighed 15st 7lbs (100kg) after the diet plan and had a BMI of 36.6 — which meant they were still medically obese. 

It did not include women with obesity who lose weight prior to trying to conceive.

In the UK, one out of eight couples fails to have children. Over 25% of Brits and 41% of Americans are overweight.

Are you more likely to get pregnant if your weight is reduced?

Patients are often advised by doctors to lose weight in order to increase their chance of becoming pregnant.

Studies show that overweight can decrease the likelihood of successful conceptions. 

Obese people have a lower chance of success. 

According to NHS guidelines, pregnant women should have a healthy body weight and follow a healthy eating routine.

Tommy’s, a stillbirth charity, says losing just a few pounds is possible.

To assist women in trying to conceive, the NHS offers fertility clinics.

However, many won’t see patients until they have reached a specific weight.

Some will even require patients to lose weight before they are considered for treatment.

Not all NHS guidelines for fertility treatment apply to everyone. This means that individual trusts are able to choose which women they will help.

The ‘postcode lottery’ allows local health care providers to ask women to weigh in at the appropriate weight to determine if they are willing to pay for the procedure.

The latest study — carried out over the four years to September 2019 — included 379 obese women who had been trying for a baby for at least a year without success. 

The average weight of each participant was 107kg (or 16t8lbs) when they started the study.

Their BMI was about 39.3 — putting them just below the morbidly obese threshold of 40.

Before the study, both partners and women were examined by a doctor and found to have good sexual health. 

Women were split into two equal groups, with one put on a 1,200 calorie diet that included two portions of fruit, three vegetables and two servings of low fat dairy — such as cottage cheese — a day. 

The trial required both women in the two groups to increase their daily step count incrementally from 6,000 to 10,000 by the end.

Those in the restricted calorie group lost an average of seven per cent of their body weight — the equivalent of 1stone 1lb (7kg). 

However, those who were in the control group maintained a similar weight. 

After 16 weeks, both sets of women were offered three rounds of ovarian stimulation and intrauterine insemination — when sperm is injected directly into the uterus to aid fertilisation. 

This treatment is not the same as IVF, where an egg is fertilized in a test tube and then implanted into the uterus. 

There were 23% of healthy babies among women who had lost weight. The success rate for those who didn’t lose weight was 11%. 29 percent were born to mothers who were not overweight. 

Researchers said that statistically, this result was the same. 

MailOnline was told by Dr Legro that he is the chair of the College’s Obstetrics and Gynaecology Department.

“It is hard for me to tell someone with obesity that weight reduction immediately before pregnancy will help her and her baby’s chances of surviving the pregnancy.

He stated that there are probably long-term metabolic advantages… but not the short-term benefits for pregnancy.

“So no, weight loss is not necessary. Prevention of obesity is the best treatment.

The British Fertility Society’s head Dr Raj Mathur was not part of the study but said that the paper raises questions about whether it is reasonable to deny fertility treatment for obese patients.

MailOnline was informed by him that the study encouraged them to examine IVF outcomes in IVF patients and whether or not a 30 year cutoff BMI is appropriate for NHS eligibility.

“I believe a flexible approach that allows for a conversation between clinicians and patients is better. 

The article appeared in PLOS MEDICAL.