Obese women who undergo rapid weight loss to get pregnant may harm rather than improve their chances of having a healthy baby, a leading researcher suggested this week. Professor Richard Legro of the Department of Obstetrics and Gynecology at Penn State University College of Medicine, Hershey, Pennsylvania, USA, said the subject was under-researched and outcomes unknown. But he pointed out that sudden and dramatic reductions in calories and increases in activity during the periconceptual period in all women, including those undergoing assisted reproduction techniques (ART), could have potentially adverse effects. Weight-loss interventions put stress on the reproductive system that could lead to failure through a variety of mechanisms, he warned.

Apart from disruption to normal physiological mechanisms, an additional concern hypothesised is that environmental pollutants stored in fat such as DDT and organochlorine, released into the blood circulation when fat is metabolised during lifestyle interventions, could have potentially adverse effects on the pregnancy.

Professor Legro is lead investigator of the multicentre National Institutes of Health (NIH) studies of pregnancy in obese women with polycystic ovary syndrome (PCOS), a leading caused of infertility. Speaking in Seville during the bi-annual Updates in Infertility Treatment (UIT2010) meeting, a prominent event in the infertility research calendar, he said the effects of extreme rapid weight loss on women undergoing infertility treatment, have never been studied in prospective rigorously designed controlled trials. “We don’t know how many calories are needed, how long women should diet, or whether they should do it at all during during infertility treatment.”

Studies of very low calorie diets in women undergoing infertility treatment where up to 8.8 per cent of body weight was lost over six weeks had been stopped after the intervention was associated with poor oocyte numbers, poor fertilisation and low pregnancy rates, he said. Similarly, intensive exercise interventions during in-vitro fertilisation (IVF) treatment had been associated with higher rates of implantation failure.

Compliance in weight loss studies is poor with up to two thirds dropping out in some studies. “The weight-loss intervention providing the most bang for your buck is bariatric surgery where up to 40 per cent of body weight is lost on average after one year and is still 30 per cent less after 10 years,” he noted. “If you follow PCOS patients after bariatric surgery it effectively cures PCOS and improves insulin sensitivity but we don’t know its effects on fecundity.” Half of women with PCOS who undergo the procedure – a form of “surgically-induced starvation” – do it because of fertility concerns but it could adversely affect outcomes in subfertile women, he warned.

“Rates of adverse maternal and neonatal outcomes may be lower in women who become pregnant after bariatric surgery compared with rates in pregnant women who are obese. However, further data are needed from rigorously designed studies.”

Women at either of the extreme ends of the body weight spectrum can find it difficult to become pregnant, remarked Professor Legro. The same is true for women undergoing IVF treatment for infertility particularly very obese women. For overweight women every one unit of Body Mass Index over 29 decreases their chance of pregnancy by 4 per cent. It has been suggested from statistical models that older, obese women with poor fertility prospects would have to lose 10 BMI points to increase their chances of conception from 10 to 20 per cent, he noted.

The received wisdom is that very thin women should be advised to gain weight and obese ones to lose it if they want to improve their chances of having a successful pregnancy. For thin women this strategy appears sound. For obese women with PCOS, routine first-line infertility treatment is to lose weight, he said. “In fact, many national guidelines defer infertility treatment for obese women with PCOS until significant weight loss has been achieved. In New Zealand for example, no ART is permitted if BMI exceeds 32.”

But weight loss is difficult to achieve, few people adhere to lifestyle intervention, and it may have no benefit in improving pregnancy in subfertile obese women. “Our current thoughts are that caloric restriction per se during preconception has harmful effects on oocyte competence. For this reason we don’t tell women to proceed with weight loss concurrently while undergoing infertility treatment,” he concluded.


Written by Olwen Glynn Owen