OTTAWA: Although obesity can significantly decrease a woman’s ability to get pregnant, losing weight through diet and exercise can improve her odds, according to a research review.
Programs that promote weight loss through lifestyle change, rather than bariatric surgery or medications, are preferred and can increase the chance of spontaneous pregnancy, the study authors conclude in the Canadian Medical Association Journal.
“It is important that women are aware that they may jeopardize their reproductive health if they are obese and should consider improving their lifestyle,” said senior author Dr Jean-Patrice Baillargeon of the University of Sherbrooke in Canada.
Infertility, which is defined as the inability to become pregnant after 12 months of trying, affects about 15% of couples in Canada, the review authors note. Infertility affects 12% of women in the United States, according to the Centers for Disease Control and Prevention.
Given that 25% of Canadian women of reproductive age are overweight and another 19% are obese, the authors write, it’s “prudent” to determine the best ways to reduce the potential impact on fertility.
“Evidence also shows that if a mother is obese during pregnancy, it increases the risk of obesity and diabetes in her kids as well,” Baillargeon, who is also president of the Canadian Society of Endocrinology and Metabolism, said in a phone interview.
Baillargeon and colleagues reviewed research published in the last 10 years on the links between obesity, fertility, lifestyle modifications and other obesity treatment options. They focused on analysing data from the 20 most relevant review articles and original research papers.
This prior research finds that the risk of infertility increases 27% in women who are overweight, and 78% in women who are obese. Obesity is defined as having a body mass index (BMI), a ratio of weight to height, of 30 or higher. BMI between 25 and 29.9 is considered overweight, and between 18.5 and 24.9 is considered a healthy weight.
Obesity most commonly harms women’s fertility through menstrual and ovulation disorders, which include polycystic ovary syndrome, the authors write. Overall, the chance of pregnancy drops 4 percent with each one-point increase in BMI. Obesity also decreases the effectiveness of fertility treatments, they note.
“Women who are obese usually need more expensive fertility treatments as well, which can be a barrier for them,” Baillargeon said. “We want women to be aware of these factors.”
Obesity can affect the pregnancy itself, the authors point out. It’s associated with higher odds of gestational diabetes, postpartum depression, and Caesarean delivery. Newborns are also more likely to be born early and have health problems such as neural tube defects or heart anomalies.
Several international health organizations recommend a 5% decrease in body weight for obese women who want to become pregnant or pursue fertility treatments. Past studies have found that women with polycystic ovary syndrome, in particular, benefit from weight loss programs because they tend to have higher central obesity and insulin resistance that could hinder pregnancy.
“These few studies don’t give solutions to all of the unanswered questions here, but on the whole, we should take notice that obesity actively interferes with reproduction,” said Dr Annemieke Hoek of the University of Groningen Medical Center in the Netherlands, who wasn’t involved in the review.
“Parents, future parents, government officials and policymakers should be aware that if the population grows fatter and fatter, we’re increasing our chances of infertility,” Hoek said in a phone interview.
Although losing weight is beneficial, women should avoid extreme dieting immediately before and during pregnancy, said Dr Richard Legro, a reproductive endocrinologist at the Penn State Health Milton S. Hershey Medical Center in Pennsylvania, who wasn’t involved in the review.
“There should be a divide between getting ready for pregnancy and actively being pregnant,” he said in a phone interview. “Women shouldn’t be dieting when their bodies need to be an energy store. It sends mixed messages to the brain.”
These mixed messages, in turn, “lead to yo-yo dieting that we want to avoid,” Legro said. “We need to focus on appropriate weight maintenance across the pregnancy cycle.”