An APRN and health coach explains what the latest research tells us about weight and pregnancy loss after embryo transfer.
August 24th, 2026 | 13 min. read
Fertility treatment can make every health decision feel high-stakes, especially when new research raises questions about weight and pregnancy outcomes. Here, we explain what the latest findings show and how to plan your next steps without shame or pressure.
AT A GLANCE
This large retrospective study examined 14,990 patients undergoing their first single euploid frozen embryo transfer (FET).
Early pregnancy loss occurred in 19.5% of patients with obesity and 15.9% of patients without obesity—a difference of 3.6 percentage points. Approximately 4 out of 5 patients in both groups did not experience early pregnancy loss.
The study found an association between BMI and miscarriage but does not prove that higher BMI caused the losses or that losing weight before IVF would prevent them.
BMI does not capture metabolic health, nutrition, body composition, sleep, stress, or individual medical circumstances, so treatment decisions should be personalized.
When you’re navigating fertility treatment, it can feel like there is a long list of things you’re supposed to do perfectly: eat the right foods, take your medications at the right time, exercise more, reduce stress, and get enough sleep.
That's a lot to carry during an already demanding season of life.
Concerns about weight and fertility can make that load feel even heavier. But supporting your health during treatment doesn't require perfection or drastic changes, and you don't have to figure it all out on your own.
The Impact of Weight on IVF Success
Weight and fertility are sometimes discussed as though BMI alone can predict whether treatment will work. It cannot.
Reproductive outcomes are shaped by many factors, including age, underlying health conditions, embryo characteristics, metabolic health, and treatment variables. BMI captures only one small part of that picture.
A 2026 study published in Fertility and Sterility examined one specific part of this broader conversation. Euploid embryos have the expected number of chromosomes. By focusing on these embryos, researchers asked a narrower question: After accounting for embryo chromosome number, is BMI still associated with early pregnancy loss?
2026 Embryo Transfer Study Findings
The retrospective study reviewed records from 14,990 patients across nine fertility centers undergoing their first frozen transfer of a single euploid embryo. Each embryo was created using the patient’s own eggs and classified through preimplantation genetic testing for aneuploidy (PGT-A) as having the expected number of chromosomes.
Focusing on this specific type of transfer helped researchers reduce the influence of one major cause of miscarriage (embryo chromosome abnormalities) and examine the relationship between BMI and pregnancy loss more closely.
Does a higher BMI increase your chance of miscarriage?
Early pregnancy loss occurred after 19.5% of transfers among patients with obesity and 15.9% among patients without obesity, an observed difference of 3.6 percentage points. Put simply, around 4 out of 5 patients in both groups did not experience early pregnancy loss.
After researchers accounted for other patient, embryo, and treatment factors, the adjusted difference was 3.1 percentage points, or approximately three more losses per 100 transfers.
Implantation rates did not differ significantly.
Patients with obesity had slightly lower rates of clinical pregnancy, ongoing pregnancy, and live birth. Pregnancy loss rates among patients classified as overweight were similar to those in the normal BMI category.
Pregnancy loss rates increased across class I obesity (BMI 30–34.9), class II obesity (BMI 35–39.9), and class III obesity (BMI 40 or higher). These findings describe an association across a large group. They cannot predict an individual outcome or establish that body weight causes pregnancy loss.
What This Research Means for Fertility Patients
This research does not mean that your weight determines whether fertility treatment will be successful. Weight alone cannot predict your chances of embryo implantation, pregnancy, live birth, or a healthy baby.
If you have previously experienced pregnancy loss, I also want you to know that these findings don't mean that your loss was a result of something you did or didn't do. We explore this difficult and deeply personal question further in Did I Cause My Pregnancy Loss?
Instead, the study adds to evidence that reproductive outcomes may be influenced by many factors beyond embryo chromosome number, including age, underlying health conditions, treatment variables, and aspects of metabolic health.
The researchers discussed several possible explanations for the association, including inflammation, insulin resistance, and changes in how the uterine lining prepares for pregnancy. However, they did not directly test these possibilities. More research is needed to understand the association and whether any intervention could change outcomes.
What This Study Can’t Tell Us
It Cannot Prove Cause and Effect
This was a retrospective observational study, meaning researchers reviewed existing patient records for patterns. This type of research can identify an association, but it cannot prove cause and effect.
To make the comparison more meaningful, researchers accounted for the patient’s age when the eggs were retrieved, whether they had given birth before, the fertility center and transfer protocol, how quickly the embryo reached the blastocyst stage, and its grade.
It Couldn't Account for Every Health Factor
The records did not include potentially relevant information such as smoking history, hypertension, diabetes, thyroid disease, ethnicity, menstrual regularity, diet, physical activity, sleep, stress, or emotional wellbeing.
The study also relied on BMI. It did not include other measures that might provide additional information about body composition or metabolic health, such as body fat percentage or waist-to-hip ratio.
Findings May Not Apply to Every Patient
Because the study included only patients transferring an embryo created with their own eggs and classified by PGT-A as euploid, the findings may not apply in the same way to patients using donor eggs, transferring untested or mosaic embryos, undergoing other forms of fertility treatment, or experiencing recurrent pregnancy loss.
It Didn't Test Ways to Improve Outcomes
The study did not evaluate nutrition counseling, health coaching, exercise, weight loss interventions, or any other strategy intended to improve embryo transfer outcomes. It cannot tell us whether any of these approaches would have changed the results.
Beyond the Scale
A quick refresher: body mass index (BMI) is a calculation based on height and weight.
It can help researchers identify patterns across large groups, but it does not directly measure body fat or individual health. BMI cannot distinguish fat from muscle or bone, show where fat is carried, or provide a complete picture of metabolic health. The Centers for Disease Control and Prevention (CDC) describes BMI as a screening measure, not a diagnostic tool.
Health is also shaped by factors BMI cannot capture, including nutrition, movement, sleep, stress, genetics, hormones, medical conditions, medications, and access to care and nutritious food.
Healthy people come in many shapes and sizes. Fertility care should focus on each patient’s individual health needs and the support that will be most useful to them.
Find Nutrition Support
Meet with an Illume Fertility registered dietitian nutritionist for practical guidance individualized to your health, treatment plan, and fertility goals.
How Illume Supports Your Health
This study did not examine nutrition counseling or its effect on embryo transfer outcomes. Nutrition counseling still provides invaluable support to patients looking to address individual needs, prepare for pregnancy, and make realistic choices during treatment.
At Illume Fertility, registered dietitian nutritionists Jill Hickey and Jenn Walsh provide personalized nutrition guidance as part of our Integrated Fertility & Wellness program.
Fertility-Focused Nutrition Guidance
You don't need to be trying to lose weight to benefit from working with a nutritionist.
Illume's Nutrition Team can evaluate your current dietary intake, health history, medications, supplements, nutrition-related lab results, and specific nutrient needs. They can also help you sort through the often-confusing nutrition advice surrounding fertility and identify changes that make sense for your body, lifestyle, and goals.
Depending on your needs, this may involve building more balanced and satisfying meals, getting adequate protein and fiber, addressing nutrient deficiencies, supporting blood-sugar and metabolic health, navigating nutrition with PMOS (formerly PCOS) or insulin resistance, managing gastrointestinal conditions or food restrictions, reviewing prenatal vitamins and supplements, or finding realistic ways to eat well during a busy treatment schedule.
The goal isn't to achieve the "perfect" fertility diet. It's about finding sustainable ways to nourish your body during treatment and as you prepare for pregnancy.
In addition to nutrition counseling, Illume's Integrated Fertility & Wellness program offers fertility acupuncture, free support groups and educational workshops, access to a vetted network of mental health providers, and more.
Health Coaching for Real Life
Sometimes we know what we would like to change, but we're not sure how to make it happen. Health coaching can help bridge that gap.
While a nutritionist assesses nutrition-related health needs and provides individualized dietary guidance, a health coach can translate their recommendations into manageable actions, help you work through barriers, and develop routines you can realistically maintain.
In my work as a nurse practitioner and a health coach, I often meet patients who believe they need to change everything about their diet and lifestyle at once. A more helpful first step is identifying one area that would make daily life or treatment feel more manageable.
Instead of approaching this with an "I need to lose weight" mentality, I always encourage patients to start with a smaller, clearly defined goal, such as:
"I will add a source of protein to my breakfast three mornings this week," or "I will take a 20-minute walk after dinner a few evenings this week." All these little actions will add up.
You Deserve Expert Guidance
During a fertility journey, having someone like a nutritionist or health coach helping you set goals, work through barriers, and recognize progress can provide something valuable: a sense of agency in a process that often feels outside your control.
Learn more about these offerings by reading our guide to working with an Illume nutritionist or visiting Fertile Health Expert for a detailed look at health coaching. All Illume patients are eligible for a free initial health coaching session with me.
Do I have to lose weight before IVF?
Not necessarily. This is an important point about the new research.
The study found an association between obesity and pregnancy loss, but it did not examine whether losing weight before embryo transfer improves outcomes. The researchers specifically identified weight loss interventions as an area requiring additional study.
A 2024 systematic review and meta-analysis found that preconception weight-loss interventions were associated with higher pregnancy rates overall but did not improve live birth rates or reduce miscarriage rates.
In a subgroup of participants undergoing fertility treatment, miscarriage rates were higher in the weight loss intervention groups. That finding does not show that the interventions caused those losses. The authors concluded that current evidence does not support a blanket recommendation to lose weight immediately before conception to improve live birth or miscarriage outcomes.
The FIT-PLESE randomized clinical trial compared an intensive preconception weight-loss program with an exercise-focused program that did not target weight loss. Among patients with obesity and unexplained infertility, the weight-loss program did not improve healthy live birth rates.
Why Timing Matters
For some patients, addressing blood sugar, blood pressure, nutritional deficiencies, mobility, sleep, or other health concerns before pregnancy may make sense. For others, the best approach may be to continue fertility treatment while incorporating nutrition, movement, and other supportive behaviors along the way.
The American Society for Reproductive Medicine (ASRM) recommends individualized counseling that weighs the potential benefits of preconception health changes against age-related fertility decline and the possible consequences of delaying treatment.
Your reproductive endocrinologist can help you consider your age, diagnosis, ovarian reserve, medical history, treatment plan, and goals before deciding what makes sense for you.
What should I focus on right now?
You don't need to completely overhaul your life to improve your health. Start small:
- Ask your Care Team which health factors are most relevant to your treatment plan.
- Request a referral to Illume’s Nutrition Team and discuss whether you have any nutritional deficiencies or lab results that need attention. These visits are frequently covered by insurance, depending on your plan.
- Choose one new meal, movement practice, or sleep goal that feels achievable.
- Avoid restrictive diets, extreme exercise regimens, and unverified fertility supplements.
Remember: If you have specific questions about weight, BMI requirements, or whether to delay treatment, don't be afraid to bring them up with your physician.
It’s About Progress, Not Perfection
Nutrition counseling and health coaching aren't meant to add more tasks to your fertility to-do list. They are about making that list (and the journey as a whole) a little easier to navigate.
You don't have to eliminate entire food groups from your diet, exercise for hours each day, reach a particular weight, or do everything perfectly to benefit from taking care of yourself.
Sometimes the most meaningful changes are the smallest ones: the breakfast that keeps you fueled through morning monitoring, the walk that helps clear your head after work, or having someone on your Care Team who can help you decide what is actually worth focusing on.
Because this isn’t just about getting through treatment. It’s about feeling strong, healthy, and empowered throughout your fertility journey and beyond.
Frequently Asked Questions
Does BMI affect embryo transfer success?
Some research has found an association between higher BMI and fertility treatment outcomes. In the 2026 study discussed here, obesity was associated with a modestly higher risk of pregnancy loss after a frozen transfer of a single euploid embryo.
However, embryo implantation rates were not significantly different, and BMI alone cannot predict an individual patient’s outcome.
Does obesity cause pregnancy loss after embryo transfer?
This study does not prove that obesity causes pregnancy loss. It was an observational study, so unmeasured health, lifestyle, or treatment factors may have influenced the results. Pregnancy loss is complex and is never evidence that a patient did something wrong.
Does losing weight before IVF improve live birth rates?
Current research has not consistently shown that losing weight immediately before fertility treatment increases live birth rates or reduces miscarriage rates. Weight loss interventions may benefit some aspects of overall health, but the decision to delay treatment should be individualized.
Free Fertility Nutrition Guide
Get actionable guidance from Illume’s nutritionists about how to build balanced meals, cut through food myths, and support optimal health.
Ask a Fertility Nurse Anything
Fertility treatment brings plenty of questions. Get honest, easy-to-understand answers from Monica Moore, APRN, in our Ask Monica Q&A video series.