Can Weight Loss Boost Pregnancy Rates?

A 10%-25% weight loss can help women considered overweight or having obesity become pregnant — even if they weren’t trying to conceive — and reduce their chances for some pregnancy-related conditions and complications, according to a new study on reproduction.

The study included patient data from nearly 250,000 women in the UK aged 18-40 years who had a BMI ≥ 25, which is considered overweight. BMI measures an estimate of body fat based on height and weight. Patients with obesity, who have a BMI ≥ 30, were also part of the study.

Women in these categories who dropped the weight with a median loss of 14% had a small increase, about 5%, of becoming pregnant in the following 3 years compared with those with stable weight, according to the study published in Human Reproduction.

The study used patient data collected from primary care practices linked to hospital records in England between January 2000 and May 2022.

Nearly 80% of the women in the study kept a stable weight and the rest lost weight. Of the women who became pregnant (9%), those who lost weight had a “statistically significant reduction” in the risk for gestational diabetes and emergency caesarean section, the study found.

The women who lost weight also saw reduced pregnancy-induced hypertension with fewer babies born considered large for their gestational age compared with women of stable weight.

Novo Nordisk — the maker of weight-loss drug Wegovy and diabetes drug Ozempic — funded the study, and most of the study authors work for the pharmaceutical company and/or hold shares or stock.

Medscape Medical News asked a few clinicians, including ob/gyns with specialized training to treat patients with obesity, to weigh in on the study’s findings.

“There is a lot of data to support that women that have obesity or are overweight have higher risks in their pregnancy but also have a more difficult time conceiving,” said Deidre Neyhart-McIntosh, MD, an ob/gyn with the Cleveland Clinic, Cleveland, who is trained in obesity medicine.

The study shows that the healthier a woman can be prior to conceiving, the easier it will likely be for her to conceive and have a more successful pregnancy, McIntosh said. In her practice, McIntosh has seen that women who lose even 5% of their body weight can reduce their blood pressure, glucose, lipids, inflammation, and cardiovascular risk.

McIntosh said she speaks with patients who want to be pregnant about the risks of having obesity, such as diabetes, hypertension, preeclampsia, preterm delivery, or cesarean section of a large baby. She advises women to try to lose weight 6 months before they want to become pregnant and to study the habits that help them lose weight to continue eating healthy during pregnancy.

Patients who are overweight may seek her help if they have difficulty becoming pregnant or have risk factors such as high blood pressure or prediabetes, she said. In those cases, McIntosh might discuss nutrition, exercise, or prescribe weight-loss medicine to help them improve their chances of a healthy pregnancy.

McIntosh finds that most of her patients have tried other methods to lose weight before requesting weight-loss medicine. Depending on the medication, they should stop the drugs either immediately prior to conceiving or 2 months beforehand.

Despite the study’s connection to a weight-loss drug maker, McIntosh said she still believes the findings are valid. “Obviously, we’re going to pick out some of the biases, but overall, they looked at a wide variety of women and didn’t focus on women that were just taking weight-loss medications either,” she said.

Weight-Loss Medications

The FDA has approved some of the newer medications for chronic weight management in adults with obesity, or if they are overweight, with at least one weight-related condition such as high blood pressure, type 2 diabetes, or high cholesterol.

Johanna Finkle, MD, an ob/gyn and weight-loss specialist with the University of Kansas Health System, Kansas City, Kansas, said that although the study doesn’t specifically mention weight-loss drugs, a weight loss of 10%-25% is typically only seen in women taking the medicine for weight loss. From her experience, diet and exercise only produce a 3%-5% weight loss in a year, Finkle said.

The study also cited previous research with different diets and exercise that didn’t show decreased pregnancy complications or increased spontaneous conception, she noted.

Finkle believes the new study looked at weight loss because women are losing significant weight on the medicines Novo Nordisk manufactures, namely GLP-1 receptor agonists.

“The question that they are trying to answer: Is this going to be beneficial to a preconception population and how much weight loss [is optimal] because these drugs are producing more weight loss than we see with diet and exercise alone,” she said.

Optimal Weight Loss

“Right now, what we counsel is about 10% weight loss of body weight prior to pregnancy,” Finkle said. “Any weight loss may be beneficial.” 

There are also risks to losing too much weight, especially in patients losing 30% of their body weight, she said. “What I’m seeing in my patients is sometimes they’re not consuming enough calories or even enough water,” Finkle said. “I’m having to remind them that they need to eat more frequently. We discuss sufficient protein.” Others may experience hair loss.

When patients lose a significant amount of weight, it can affect pregnancy. Patients who had bariatric surgery have a risk for preterm delivery, Finkle said. “I worry about small-for-gestational-age babies and an increased risk for miscarriage when people have a rapid trajectory of weight loss,” she said.

Finkle said she counsels patients who are rapidly losing weight to try not to conceive while on the medication because “the data on teratogenic risk of the weight-loss medications is not yet known.”

Ideally, patients who want to lose weight before they conceive should come to her a year in advance, Finkle said. “But if they’re wanting to conceive in 3 months, then we discuss healthy behaviors, lifestyle, nutrition, and exercise counseling. We discuss: What is your goal? When do you want to conceive and how does weight loss play a role in that? How much weight loss can we achieve?” she said.

Research Implications

While previous research may have focused on the outcomes of women undergoing fertility treatment, the Novo Nordisk study wasn’t restricted to women trying to conceive, so study authors said that the benefits of weight loss may be greater in women who are actively trying to become pregnant.

Erin LeBlanc, MD, who conducts similar research about weight loss and pregnancy, believes the Novo Nordisk study provides further evidence that women having trouble becoming pregnant because they are overweight or have obesity could benefit from weight loss. In other words, if having a higher BMI is associated with decreased fertility rates, weight loss among that population could have the opposite impact, she said.

LeBlanc, an epidemiologist and endocrinologist with the Kaiser Permanente Center for Health Research, said the Novo Nordisk study also aligns with research she led showing that women who lost weight had lower rates of gestational diabetes in early pregnancy. Because some women in the clinical trial gained weight back later in pregnancy, she stressed the importance of weight management throughout pregnancy.

Women in her study who met with health coaches weekly for 6 months and then monthly for 18 months or until the end of their pregnancy were able to start pregnancy at a healthier weight.

However, they experienced more weight gain during pregnancy, likely because it was challenging to maintain the healthy lifestyle changes they made prepregnancy without ongoing support, she said of the study originally published in 2021 in the American Journal of Obstetrics & Gynecology.

“What I would say from my research is that if women have been able to lose weight before pregnancy, they just need to be sure that they get support during pregnancy to help them to maintain a healthy lifestyle,” LeBlanc said.

LeBlanc also said the new study may help inform future recommendations from the National Academy of Medicine, formerly the Institute of Medicine, which advised in 2009 that women achieve a healthy weight before becoming pregnant and remain within the gestational weight gain guidelines during pregnancy.

Women with a healthy weight should gain 25-35 pounds; women who are overweight, 15-25 pounds; and women with obesity, 11-20 pounds, according to those guidelines.

Study Limitations

Among the limitations of the study, Finkle said using participants from the UK cannot necessarily be applied to those from the US. “They did not cite the composition of their patient population,” she said. “The United States is very diverse.” 

Finkle said that the median age of the patients (30 years) is also important to note. “When you are talking about fertility, age plays a much larger role than necessarily body weight when looking at someone’s ability to conceive.” 

Study authors said they didn’t know whether women had intended to become pregnant or whether that intention was why they lost weight.

Including women who don’t intend to conceive may also affect the findings by underestimating the relationship between weight loss and chance of pregnancy, the authors said. And while they observed a link between weight loss and increased chance of pregnancy, they said they couldn’t imply higher pregnancy rates were caused by weight loss.

In her practice, Finkle often sees patients trying to lose weight prior to conception.

“So if more patients in the group that was actually trying to lose weight wanted to conceive, they’re going to have higher rates of pregnancy than a weight stable group that maybe wasn’t trying or had any intention of conceiving and were using maybe other methods to prevent pregnancy,” she said.

Overall, Finkle found promising the study’s finding of a small increase in conception from weight loss. She said more studies are needed to look at weight loss and pregnancy, including how weight gain during pregnancy affects the delivery and health of the mother and child.

“There’s this phenomenon called weight cycling,” Finkle said. “You may lose weight, then regain the same — or more — during pregnancy, and the question becomes: How will that affect outcomes such as large-for-gestational-age babies, cesarean-section deliveries, or hypertensive disorders? Many questions remain unanswered.” 

Roni Robbins is a freelance journalist and former editor for Medscape Business of Medicine. She’s also a freelance health reporter for The Atlanta Journal-Constitution. Her writing has appeared in WebMD, HuffPost, Forbes, New York Daily News, BioPharma Dive, MNN, Adweek, Healthline, and others. She’s also the author of the multi-award–winning novel Hands of Gold: One Man’s Quest to Find the Silver Lining in Misfortune.