May 2024 Issue

Improving IVF Outcomes
By Carrie Dennett, MPH, RDN
Today’s Dietitian
Vol. 26 No. 5 P. 28

Learn how dietitians can make a difference with nutrition and lifestyle interventions.

At press time, access to in vitro fertilization (IVF)—the joining of an egg and sperm in a laboratory dish—was threatened in Alabama following a landmark ruling by the state’s supreme court, stating that embryos have the same legal rights as children and therefore have personhood status.

Following the ruling, many IVF clinics in Alabama shut down to pause IVF services for fear of criminal prosecution. However, after Alabama state lawmakers passed a bill to protect IVF facilities from criminal liability, they planned to reopen, paving the way for women to resume or begin treatments to start or expand their families.

This event comes at a time when the number of women using IVF to become pregnant is on the rise.1 But even when women have unencumbered access, IVF and other assisted reproductive technologies are expensive, and they don’t guarantee conception. Nutrition and lifestyle can increase the odds of success and possibly make assisted reproductive technology unnecessary, but many women don’t seek nutrition care during this important phase of their lives. Read on to learn more about what impacts fertility and the role nutrition and lifestyle interventions may play in boosting the odds of women becoming pregnant.

Complexity of Infertility Rates
IVF is increasingly becoming more common because infertility is becoming more common, but the reasons are complex, says Angela Thyer, MD, FACOG, DipABLM, a reproductive endocrinologist and founding partner of Seattle Reproductive Medicine. “It could be due to social trends like delaying childbirth and starting a family.2 We’ve also seen changes in lifestyle, such as reduction in diet quality and an increase in sedentary behavior and jobs, which also can play a role in fertility.” Thyer says some women and men who aren’t ready to start a family are pursuing IVF because they know that fertility declines with age. “They’re choosing to preserve their fertility by freezing eggs or sperm or creating and freezing embryos at their current age rather than waiting and doing it in the future.”

“Forty is the new 30” is a catchy phrase that holds some truths, but not when it comes to fertility—even when someone is healthy. “Biologically, the ovaries are still aging at the same rate they always have,”3 Thyer says. “There’s a steady decline in both the quality and reproductive potential of both eggs and sperm. Eggs are affected more dramatically, but sperm also are affected by age.”

Thyer says female fertility starts to decline after age 30 because of declining egg quality4—which also means that IVF success rates decline with age. This comes as an unwelcome surprise to many women who think IVF is going to be the answer, only to find out they’re likely to need more than one round of IVF, and even then, success isn’t guaranteed. “Sometimes people come in and they want more than one child. If they’re starting later, in their mid 30s, getting that second baby might be even harder than getting the first baby,” Thyer says. For example, a woman using IVF who wants two children has a 90% chance if she starts trying at age 31 but a 50% chance if she starts at age 39.5 “After age 40, the success rates are very limited,” Thyer says. “People could spend a lot of time and money and effort for a very low potential chance of success. Each person is unique and obviously should be evaluated, but the age thing is hard to get around.”

Judy Simon, MS, RDN, CD, CHES, FAND, director of Mind Body Nutrition in Bellevue, Washington, says some people perceive a stigma about reproductive technologies—for example, that doing IVF isn’t natural—so they may decide to try to conceive “naturally” for another year or two, not realizing that egg reserve and egg quality is continuing to decline. “Then they seek fertility treatment and are shocked to learn how low their odds of conceiving are,” she says. “Their options end up being donor eggs or donor sperm, which is even more complex and more expensive.”

Impact of BMI on IVF, Fertility Outcomes
While age affects fertility, what about a woman’s weight? It’s not uncommon for women to believe they need to lose weight to help improve fertility or ensure a healthy pregnancy. Indeed, many women over a certain BMI may be told by their doctors to lose weight before trying to conceive. Thyer says observational data on fertility rates and BMI does show that fertility rates decrease at both the lowest and highest ends of BMI. “So, if somebody is underweight or overweight, it can affect fertility,” Thyer says. “The peak in general for fertility is around a BMI of 23 to 24.” This is also consistent with data on IVF from the Society for Assisted Reproductive Technology (SART) database (, which shows lower success rates at BMIs below 18 and above 45.

Because of this observational data, Thyer says women often are encouraged to gain or lose weight to get into the “normal” BMI range. When someone has anovulatory infertility due to polycystic ovary syndrome (PCOS) or other causes, some studies show that losing a small amount of weight can allow normal ovulation to resume. Similarly, when a female is underweight and not having menstrual cycles, meeting nutritional and energy needs and gaining some weight may trigger ovulation. In both cases, this can allow conception to occur.

However, Thyer says more recent, well-designed studies have found that, in general, weight loss doesn’t increase IVF success rates in women with higher BMIs.6,7 “In fact, it can delay treatment initiation if somebody says, ‘You should take six months and lose weight and then start your treatment,’” she says. “Then you’re six months behind, and sometimes age is a stronger factor and a stronger predictor of your success rate than weight.”8 Thyer says observed trends with weight come from population-based observational data sets that aren’t based on individuals. “I think it’s a little bit dangerous to make assumptions on a given individual’s chance of success based on their body weight, just lumping them in with the general public or population data.” She says often-cited cohort studies may find statistically significant conception rates based on BMI, but those rates aren’t clinically significant.9

Research from Brigham and Women’s Hospital in Boston presented at the 2023 American Society of Reproductive Medicine (ASRM) conference looked at eight years of IVF cycles among women with BMIs of 30 to above 50. The research found that IVF and obstetrical and neonatal outcomes were similar among the women, concluding that “IVF should not be withheld as a treatment modality for patients with obesity.”10 Thyer says many outpatient IVF clinics have BMI cutoffs because their anesthesia provider does—patients with higher BMIs are at higher risk of having a “difficult airway.”6 On the other hand, IVF clinics in hospitals providing tertiary care have the ability to intubate patients, which Thyer says is rarely, if ever, necessary.

“We’re more worried about people who get information to just lose weight, and then do so in an unhealthy way by restrictive dieting, intermittent fasting, or keto, where they’re not providing their body the nutrients it needs when they’re planning fertility treatments. That’s actually a disadvantage that’s going to hurt them more,” Thyer says. “In the rare situation when weight loss is needed, let’s say somebody has a BMI of 52 and they have to get under 40, they should still receive guidance and work with a dietitian to ensure they’re meeting their nutrient needs and energy needs. But if somebody has a BMI of 38, they should just meet their nutritional needs. They don’t need to lose weight first.”

Role of Nutrition and Lifestyle
Research supports the role of nutrition in improving fertility and IVF outcomes, yet many patients undergoing fertility treatments aren’t adequately meeting their nutritional needs. The reasons are a complex mix of food access, kitchen skills, the food environment, nutrition misinformation—and a general lack of awareness that nutrition can make a difference.

“I think the food environment and our relationship to food has really changed over the past 50 years,” Thyer says. “Ultraprocessed foods make up 60% of most Americans’ diets. There’s a lot of eating out. There’s a lot more eating on the go, not taking the time or having the time to cook meals. There’s less skill and knowledge about how to nourish yourself, how to eat competently. And I think people just eat what’s in their environment, not realizing that what’s in their environment may not be what their body needs.” For example, Thyer says many people eat more meat and animal products than they need, to the detriment of not eating as many plant-based proteins—such as legumes and soy—and fish, which are more beneficial for fertility.11

Simon says there’s much misinformation on nutrition and fertility from social media and other sources. “Our patients come in saying, ‘I thought I shouldn’t eat grains and dairy.’ They’re restricting half the foods that actually could be fertility promoting.11 Some women spend hundreds of dollars on supplements that have little or no evidence and could potentially be harmful.”

In 2011, Simon and Thyer started the “Food for Fertility” program in Seattle. “We thought, let’s teach those basic cooking skills and really increase the self-efficacy of the women we were working with to increase their confidence,” Simon says. “They would be exposed to maybe four new recipes. We never did expensive recipes. They were easy to make. They could bring the extras home so their partners could try it. It was really a hit.”

Thyer says she and Simon encourage their patients to have fun in the kitchen. “We want them to learn how to become a little more of an intuitive cook. What can you substitute or add to make foods taste good? Nobody wants food that doesn’t taste good. When you play around in the kitchen with your food and have fun, you’re going to want to eat more. You’re going to experiment more. You’re going to try new foods. We’re telling people what to add and how to do it, not as a prescription, but to have fun with it—and it’s going to also improve their fertility.”

Patients also appreciate learning why the right foods matter, Thyer says. For example, plant-forward dietary patterns that focus on minimally processed fruits and vegetables, whole grains, legumes, nuts, fish, and mono- and polyunsaturated oils—which in turn are rich in B vitamins, fiber, and omega-3 fats, while being low in saturated fat and sugar—reduce inflammation, aid embryo implantation by promoting a healthy uterine environment, and provide antioxidants for improved egg and sperm function.12-14 “Pro-fertility” diets characterized by higher intakes of supplemental folic acid, vitamin B12, vitamin D, low pesticide fruits and vegetables, whole grains, seafood, dairy, and soyfoods may enhance the body’s capability to synthesize, repair, and methylate DNA, suppress oxidative stress and support antioxidant defense, reduce systematic inflammation, and regulate glucose and insulin metabolism.11

“It’s more important for women of any size to focus on health behaviors and health outcomes rather than weight loss,” Simon says. “In our Food for Fertility classes, we focus on food and nutrition and exercise. We saw anecdotally over the years that when these women got healthier, some of them didn’t even have to go for IVF; they started ovulating and they got pregnant. We had so many stories like that with women of varying BMIs. I think the tides are turning from a less weight-centered to a more weight-inclusive approach, and that’s what we advocate. It really takes the pressure off women.”

Thyer adds, “Unless their fertility clinic has specifically told them they have a weight goal that they must hit, most patients are very excited to learn that that weight loss is not a goal. The weight loss is not necessarily the thing that helps their fertility. It’s improving nutrition, moving more, lowering stress, getting better sleep. You know, all those other things that are within your control to do, those are all behavioral things that are actionable. Nobody can make a number on a scale change by wishing it or doing a behavior.”

However, some fertility physicians may recommend weight loss in part because higher weight is associated with a higher risk of certain pregnancy complications, such as gestational diabetes, hypertension, and preterm birth, Thyer says. “They’re hoping they can avoid some of these complications, but we know that weight loss is rarely sustainable,” Thyer says. “We’ve seen over our many years of experience that with nutritional and lifestyle changes they have much lower rates of complications because they’re feeding their body well—and they’re continuing after pregnancy. This is lifetime advice. This isn’t just advice for trying to get pregnant or so pregnancy outcomes are better.”

The success Thyer and Simon have seen among women struggling with infertility inspired them to write the book Getting to Baby: A Food-First Fertility Plan to Improve Your Odds and Shorten Your Time to Pregnancy, which was released in April 2024. The book includes favorite recipes and kitchen skill-building tips from the Food for Fertility classes, along with lifestyle medicine information on fertility boosters (ie, sleep, movement, stress management) and fertility disruptors (ie, processed foods, alcohol, caffeine, tobacco, cannabis, and environmental toxins.) The result is a comprehensive, evidence-based book that patients, dietitians, and fertility doctors can find useful. “We didn’t want it to be rule-based, but we did want to give guidance,” Simon says. ”We have a lot of citations and references, but our favorite part was adding the stories from women that we worked with over the years. What were their challenges, their successes?”

Simon says many of her fertility patients aren’t focused on just getting pregnant—they want to have a healthy pregnancy, be able to breast-feed, then think about their next pregnancy. “I think it’s a really good time in someone’s life. And although our book and our classes have focused on women, everything also is helpful for sperm and sperm health. It’s not all on the woman to make changes. If she has a partner and is working with a partner, they should be making these changes, too.”

More Dietitians Needed
Many dietitians are interested in fertility nutrition. Simon says that when she entered the fertility nutrition space about 20 years ago, it was largely empty. “I didn’t have any role models. I had to take what I knew from my training in preconception nutrition and prenatal nutrition, which really didn’t address fertility, and become an expert in PCOS because it’s one of the common reasons women experience infertility. I had to go to the fertility conferences so I could really understand fertility 101 and the treatments that men and women were undergoing.”

Dietitians wanting to offer fertility nutrition need to fully understand the terminology, Simon says. “If a patient comes to see you, they’re going to rattle off all these letters, and if you don’t know the lingo, you’re going to be like a deer in the headlights. Your patient might know more than you about fertility.” For learning resources, she recommends the Women’s Health and Vegetarian Nutrition dietetic practice groups, SART, ASRM, The American College of Lifestyle Medicine, and RESOLVE: The National Infertility Association. Another resource for dietitians is Early Life Nutrition Alliance, an international team of dietitians who specialize in fertility and prenatal nutrition. The organization also offers a comprehensive group coaching program that certifies dietitians in fertility nutrition.

“I would speak at fertility conferences, and the doctors would be excited. They would say, ‘We don’t know any dietitians. Nobody’s reaching out to us.’ I’m happy to say that I see more dietitians, literally a handful, at the ASRM conferences. We need to have even more.”

— Carrie Dennett, MPH, RDN, is the nutrition columnist for The Seattle Times, owner of Nutrition By Carrie, and author of Healthy For Your Life: A Non-Diet Approach to Optimal Well-Being.


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