Dietitians specialising in fertility nutrition often get questions about the relationship between Body Mass Index (BMI) and In Vitro Fertilization (IVF) outcomes. Let’s explore this important topic and understand how your BMI might affect your IVF journey.
What is BMI?
First, let’s clarify what BMI actually is. BMI is a simple measure that uses your height and weight to work out if your weight is healthy. BMI is calculated by dividing weight in kilograms by height in metres squared (kg/m²). While it’s a useful screening tool, it’s important to note that BMI doesn’t distinguish between muscle mass and fat mass, meaning that a person might have a high BMI solely because they have a lot of muscle instead of fat.
BMI categories are generally defined as follows:
- Underweight: Below 18.5
- Normal weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obese: 30 or greater
The Impact of BMI on IVF Success Rates
Research has consistently shown that BMI can impact IVF success rates. Here’s what we know:
- Overweight and Obesity: Studies have found that women with a BMI over 25 may have lower IVF success rates. A large systematic review found that overweight and obese women had lower rates of clinical pregnancy and live birth compared to women with a normal BMI.
- Underweight: Being underweight can also negatively impact fertility. A study published in 2017 found that women with a BMI under 18.5 had lower live birth rates following IVF compared to women with a normal BMI.
- Normal BMI: Women with a BMI between 18.5 and 24.9 tend to have the highest IVF success rates.
So what is the optimal IVF BMI and why does it matter?
Many fertility clinics, even the NHS, recommend a BMI between 19 and 30 before starting IVF treatment. These limits are based on research showing that BMI impacts fertility and IVF outcomes in various ways:
- Hormone Balance: Adipose tissue (fat) produces estrogen. Too much or too little body fat can disrupt the delicate balance of reproductive hormones.
- Egg Quality: A study suggested that being overweight or obese may negatively impact egg quality.
- Implantation: Obesity has been associated with lower implantation rates in IVF.
- Impact on IVF procedures: Having a higher BMI can lead to increased cycle cancellation rates, a higher amount of medications required, and a higher number of treatment cycles are often required to achieve pregnancy.
- Pregnancy Complications: A high BMI raises complications like gestational diabetes, hypertension, and blood clots, potentially impacting IVF outcomes.
Considering BMI and IVF for men
Several studies have found associations between BMI and various aspects of male fertility.
- Sperm Parameters: Research has shown that both low and high BMI can negatively affect sperm quality. A study found overweight and obese men had reduced sperm count and concentration compared to those with normal BMI.
- Hormonal Imbalances: Obesity in men has been linked to hormonal imbalances that can affect fertility. A study in the “Journal of Andrology” reported that obese men tend to have lower testosterone levels and higher estradiol levels, which can impair sperm production.
Approaching weight management before IVF
When fertility is a concern, it’s crucial to approach weight management thoughtfully and holistically. The method chosen for weight loss or gain should prioritise hormonal balance, nutritional adequacy, preservation of muscle mass, stress reduction, and long-term sustainability.
Avoid crash diets
Crash diets, extreme exercise regimens, or rapid weight gain through poor nutrition may sound appealing but can harm fertility, even if weight goals are met.
Focus on nutritional quality
The quality of nutrition during weight change is vital for reproductive health. A nutrient-dense weight loss diet ensures sufficient fertility nutrients like folate, iron, and omega-3s while supporting egg and sperm quality. On the other hand, rapid weight gain through a poor diet may lead to nutrient deficiencies despite calorie surplus, it can negatively impact egg and sperm quality.
Choose sustainable methods
We cannot overlook the psychological impact of being turned away from IVF for having a BMI outside of the accepted range. Desperation to change our weight as soon as possible can lead us to follow extreme methods that can be detrimental to us. Sustainable methods that promote gradual weight change, create long-term healthy habits, reduce stress and promote overall well-being are the best direction to go in. Stress reduction supports healthy cortisol levels, benefiting reproductive hormones and fertility outcomes.
Lifestyle Factors Beyond Diet
Managing weight extends beyond just what we are eating, taking a look at your whole lifestyle and identifying areas in which you could make changes can support your journey and the progress you make. Here are some things to consider.
- Exercise and physical activity
Engaging in moderate physical activity can enhance IVF success rates and well as support weight management. However, avoiding excessive exercise is important, as high-intensity workouts can have negative effects
- Stress Management:
High-stress levels can negatively impact IVF success rates and stress can be a factor in emotional eating . Incorporating stress reduction techniques could support your weight loss journey as well as your fertility journey.
- Sleep
Adequate sleep is important for hormone balance, fertility and overall health. Getting enough sleep is also important for regulating the hormones that control our appetite. Aiming for 7-9 hours per night and working on sleep hygiene can support your journey.
What Can You Do?
If you have a higher BMI and are planning for IVF, here are steps to help you start your journey toward success:
- Consult a Registered Dietitian or Nutritionist: A dietitian can help you develop a personalised nutrition plan to achieve a healthier BMI. Book an appointment in our Fertility Nutrition Clinic to get 1-1- support.
- Focus on Nutrient-Dense Foods: Regardless of whether you need to gain or lose weight, focusing on nutrient-dense whole foods can improve your overall health and fertility.
- Regular Exercise: Physical activity can help manage weight, improve insulin sensitivity, and support your mood, all of which are important and beneficial for fertility.
- Manage Stress: Stress can impact both weight and fertility. Consider stress-reduction techniques like meditation or yoga.
- Be Patient: Healthy, sustainable weight change takes time. Aim for gradual changes rather than crash diets.
Remember, BMI is just one factor in fertility and IVF success. Other factors like age, underlying health conditions, and male partner factors also play crucial roles.
There are many ways to enhance egg quality sperm quality and support outcomes through diet and lifestyle changes. Often creating a fertility-supporting diet can lead to beneficial weight change.
For further evidence-based supporting on creating a fertility-friendly weight loss diet, creating a positive mindset and supporting chances of IVF success check out our Weight Loss for Fertility Meal Plan & Guide.
Conclusion
While BMI can impact IVF success, it’s important to remember that many women outside the “normal” BMI range successfully conceive through IVF. Your BMI is just one piece of the puzzle. The most important step is to work with your healthcare team, including a registered dietitian, to optimise your health for fertility and pregnancy.
Everybody is different, and what works for one person may not work for another. Always consult with your healthcare provider before making significant changes to your diet or lifestyle, especially when undergoing fertility treatment.
