How does weight affect fertility?

Weight can play a crucial role in fertility, impacting both the ability to conceive and maintain a healthy pregnancy. Underweight and overweight individuals may face challenges with ovulation, hormone balance, and overall reproductive health.

This article explores how weight influences fertility and discusses steps that can be taken to improve your fertility through weight management and proactive steps to increase overall health.

How much does weight affect fertility?

There are many factors that impact fertility including age, smoking, alcohol consumption and medical conditions. Weight is another lifestyle factor that can have a significant impact on both male and female fertility.

Female fertility and weight

For some women, being underweight or overweight can make it harder to fall pregnant. For example, having a body mass index (BMI) of 18.5 or less can cause your body to stop making oestrogen which in turn, can result in irregular periods and an inability to ovulate.

Women with a body mass index over 27 are three times more likely than women in the normal weight range to be unable to conceive because they don’t ovulate. Excess weight can also negatively impact egg quality with each unit of BMI above 29 lowering the chance of achieving a pregnancy within a year by around 4%.

There are many other reproductive health factors that can be influenced by being overweight:

•  Hormonal imbalances: Excess body fat can lead to elevated levels of oestrogen, which may disrupt the hormonal balance needed for regular ovulation.

•  Irregular menstrual cycles: Overweight individuals may experience irregular or absent periods (anovulation), making it harder to predict fertile windows.

• Polycystic Ovary Syndrome (PCOS): Being overweight is often linked to PCOS, a common condition that causes irregular periods, anovulation, and cysts on the ovaries, all of which impact fertility.

• Insulin resistance: Excess weight can lead to insulin resistance, which in turn can cause higher levels of insulin in the blood. This can interfere with ovulation and lead to reproductive issues.

•  Increased risk of miscarriage: Overweight individuals may have a higher risk of miscarriage due to hormonal imbalances and related health conditions.

• Reduced success with fertility treatments: Being overweight can lower the success rates of assisted reproductive technologies like IVF, as it can affect egg quality, implantation, and overall reproductive health.

• Inflammation: Excess weight is associated with chronic low-grade inflammation, which can negatively impact reproductive functions and embryo implantation.

Male fertility and weight

There has been a 300% increase in the number of obese reproductive age men in the last 30 years and this has coincided with rise in male infertility across the globe. Excess weight has been found to be detrimental to sperm quality and negatively impact the germ cells in the testes that develop into sperm.   

Weight also influences the amount of sperm that men produce. Overweight men are 11% more likely than men with healthy BMIs to produce low numbers of sperm and 39% more likely to experience azoospermia (where the semen contains no sperm at all). Obese men are 42% more likely to have a low sperm count and 81% more likely to produce no sperm.

There are additional ways in which being overweight can affect fertility in men:

• Hormonal imbalances: Excess fat can convert testosterone into oestrogen, leading to lower testosterone levels, which can impair sperm production and libido.

•  Erectile dysfunction: Obesity is linked to vascular and hormonal issues that can contribute to difficulties with erections, affecting overall reproductive performance.

• Testicular overheating: Extra fat in the thigh and pelvic areas can raise the temperature around the testes, which negatively impacts sperm production and quality.

•  Insulin resistance: Similar to women, insulin resistance in overweight men can lead to hormonal disruptions, which can decrease sperm health and reproductive function.

•  Inflammation: Excess weight can lead to chronic inflammation, which may damage sperm DNA.

• Reduced success of fertility treatments: Overweight men may face lower success rates with fertility treatments due to poorer sperm quality.

Can I get pregnant if I am overweight?

Yes, it is possible to get pregnant if you are overweight, and many women with high BMIs successfully fall pregnant naturally. However, you may not find it as easy as someone with a lower BMI. One study found that 81% of women of a healthy weight conceived within one year of stopping contraception compared to 66% of obese women.

Being overweight also increases the chances of complications for you and your baby should you fall pregnant. For example, overweight women are at higher risk of:

•  Miscarriage

• High blood pressure

• Pre-eclampsia

• Gestational diabetes

• Blood clots

• The baby’s shoulder’s becoming stuck during labour

• Heavier post-partum bleeding

What is the weight limit to get pregnant?

There is no definitive weight that will prohibit someone from becoming pregnant. Woman of all shapes and sizes have perfectly routine pregnancies and births and deliver healthy babies. However, being in good health is important for conception and for carrying a pregnancy and so reaching your optimum weight can help improve your chances of falling pregnant.

If you are having fertility treatment, it is desirable to have a Body Mass Index (BMI) under 30, which is the NHS eligibility cut-off, however, some private clinics will accept higher BMIs, usually up to 35, and in some cases will go beyond this with additional assessments on a case-by-case basis. A BMI of between 20 and 25 is ideal with the correct level of body fat as people with a BMI of under 19 may also not be eligible for treatment. This is because both too much and too little body fat can affect fertility, IVF success and miscarriage risk.

Does losing weight help fertility?

When it comes to how to increase your chances of getting pregnant, even a small amount of weight loss can be beneficial. A systematic review and meta-analysis of existing evidence found that diet and exercise improved the regularity of menstrual cycles, helped achieved ovulation and increased pregnancy rates. In instances where women were losing weight in the hope of pursuing fertility treatment, many were able to conceive naturally following weight loss without any additional interventions.

For men, the data suggested that a combination of diet and exercise resulted in improvements in sperm concentrations, motility, morphology and sperm DNA integrity.

Losing weight sustainably for pregnancy

Whilst weight is not the only factor in fertility, weight loss is generally recommended as first-line therapy, particularly for those with PCOS or before trying to conceive, because it has been shown that losing 5% of your body weight can significantly improve PCOS symptoms including regulating periods and improving fertility.

During pregnancy, having a high BMI increases the risk of developing problems such as gestational diabetes and pre-eclampsia and once you are pregnant it is not recommended to diet, so it is worthwhile focusing your efforts on weight loss before conception if weight loss is something you want to achieve. 

We have to be realistic, losing weight can be extremely difficult and yoyo dieting and restrictive diets can have a negative effect on our health leaving us with below optimum nutrient levels.  Therefore, it can be helpful to seek specialist support from a registered nutritionist or dietician who can take into consideration your medical history and individual needs. They can support you in a healthy approach to weight loss that is sustainable, so you can prepare for conception and access fertility treatments.

Here are our top weight loss tips:

Fertility and nutrition are closely linked which is why the Mediterranean style diet is a great foundation for both a weight loss diet and fertility optimising diet as it contains the key nutrients required to improve egg quality, ovarian function and sperm health but also is also well balanced in terms of food groups.

A lower carbohydrate (not too low) and higher protein diet may be able to help support weight loss; however, it is still important not to go too low with carbs especially as they give us energy.

Lower glycaemic carbohydrates such as beans, pulses, fruit, veg and whole grains are good choices as they help to balance your blood glucose levels and combined with protein can also help you feel fuller for longer.

Opt for healthy sources of fat such as olive oil, avocado, nuts and seeds over saturated fats such as cakes, pastries, coconut oil and butter. Fats will keep you satisfied, are crucial for our hormones and are needed to absorb fat-soluble nutrients like vitamin D which is important for fertility.

Keep up or start regular movement and exercise as this will help to maintain your metabolism.

Sleep is extremely important when it comes to weight loss and often gets neglected, but a lack of sleep can really impair your appetite-regulating hormones affecting what you eat throughout the day and encouraging you to opt for higher carb and more sugary and high-calorie foods.

Stress management is another important factor, especially if you are an emotional eater or use food to cope with negative emotions and have the added stress of fertility struggles. Develop an emotional tool kit with mindfulness practices such as journaling, yoga and meditation.

If you are in a couple, focus on the positive dietary changes together and help one another out.

Seek support from a registered nutritionist or dietician to help you to achieve your weight loss goal.

If you have been trying to conceive without success and are exploring your next steps, Apricity is here for you. We offer at-home fertility tests that can help provide insight into whether your weight may be influencing your fertility and can provide recommendations for treatments and support that can help you get in the best health possible before beginning fertility treatment such as IVF. If you’d like to find out more, you can book a free consultation with an Apricity advisor.