Obesity & infertility often go hand in hand. Obesity reduces fertility, and it is well known that a high body mass index (BMI) lowers pregnancy rates in in vitro fertilization (IVF).
This is why many fertility specialists refuse to begin treatment for obese women until their BMI returns to normal levels. Naturally, this advice is for their own benefit, since what doctors truly want is for their patients to achieve pregnancy. However, the issue is far more complex than it appears at first glance.
No one wants to be obese, and most women who are overweight have already tried everything to lose weight and regain their figure. After all, overweight people don’t need a doctor to tell them they should lose weight; they already know it. But (as most of us can confirm from personal experience), losing weight is extremely difficult.
For many of us, every time we lose one kilogram, we end up gaining back two. This is, of course, very discouraging, and hearing others point out that you are overweight can make you feel not only hurt but also offended.
The problem becomes even greater if you are also infertile. Many people will tell you that your obesity is the reason you are not getting pregnant, and that makes you feel even worse about yourself. Not only can you not lose weight, but you also cannot have a baby! Moreover, some doctors may even be rude and refuse to take on women with infertility until they manage to bring their BMI back to ideal levels.
This is certainly unfair and harsh. No overweight woman wants to be overweight. Many have tried everything possible to lose weight, but simply haven’t succeeded. It’s a common tendency for some to accuse them of lacking willpower, but this only makes matters worse because it adds guilt. When a doctor refuses to treat them because of obesity, they feel trapped and hopeless, and this can often lead to gaining even more weight. They no longer feel like going out or exercising, and out of self-pity, they stay home and eat more, without knowing how to break the cycle. Infertility and the inability to lose weight further lower their self-esteem and lead to a vicious circle.
Doctors need to learn to be kinder to women who are obese. Suggesting that they “just lose weight” is easy, but if the woman insists that she has already tried and failed, or if she follows a program of her own and still doesn’t succeed, doctors should not refuse to treat her. By discouraging her, they make the situation worse, because she will spend precious time trying to lose weight instead of trying to conceive, and that is valuable time that cannot be recovered.
How should we approach overweight women?
Specific solutions are needed, with a well-structured weight loss plan, where fertility specialists help them follow it in collaboration with dietitians, physical therapists, and fitness trainers. They must also show compassion and appreciate that these women have done everything possible to lose weight, regardless of whether they have succeeded or not.
There is no reason to refuse treatment to them, regardless of what certain guidelines might say. Instead of focusing on BMI, it would be far better to focus on the patient herself.
How excess weight affects ovulation
Fat tissue is not an inactive energy store. It works like an endocrine gland, producing hormones and substances that directly affect the reproductive system.
- Insulin resistance: high insulin levels stimulate the ovaries to produce more androgens. Follicles stop maturing normally and ovulation becomes irregular or stops.
- Excess estrogen: fat tissue converts androgens into estrogens. Constant exposure, without the normal fluctuations, disrupts the hypothalamic-pituitary-ovarian axis.
- Reduced SHBG: the protein that binds sex hormones decreases, so more free androgens circulate.
- Chronic low-grade inflammation: it appears to affect egg quality and endometrial receptivity.
This is why even women with higher weight who have regular cycles take longer, on average, to conceive. The good news is that most of these mechanisms improve with moderate weight loss.
Body mass index and waist circumference: what we measure
Body mass index (BMI) is calculated by dividing your weight in kilograms by the square of your height in meters. A woman who is 1.65 m tall and weighs 82 kg has a BMI of about 30. According to the World Health Organization:
- 18.5 to 24.9: normal weight.
- 25 to 29.9: overweight.
- 30 and above: obesity, with further classes at 35 and 40.
BMI is useful, but it does not tell the whole story. It does not distinguish muscle mass from fat, and it does not show where the fat is. A waist circumference above 80 cm in women, and especially above 88 cm, indicates abdominal obesity, which is more closely linked to insulin resistance. That is why your doctor assesses both, together with blood sugar and lipid tests.
The man's weight matters too
The discussion about weight almost always focuses on the woman. But obesity also affects male fertility, through several mechanisms:
- Fat converts testosterone into estrogens, which reduces sperm production.
- Higher temperature around the scrotum puts a strain on sperm production.
- Erectile dysfunction and sleep apnea are more common and affect both hormones and sex life.
- Sperm DNA damage occurs more often.
Weight loss, exercise and quitting smoking improve sperm within about three months, the length of one cycle of sperm production. You will find more about evaluating the male partner in the guide on male infertility.
A realistic weight loss plan before conception
Strict diets rarely last. What works is small changes you can maintain, with the support of specialists.
Nutrition
- Aim to lose about half a kilo to one kilo per week.
- A Mediterranean pattern: vegetables, legumes, whole grains, fish, olive oil.
- Fewer soft drinks, juices and processed foods, which raise insulin quickly.
- Working with a dietitian, especially if you have polycystic ovaries or prediabetes.
Exercise and sleep
- At least 150 minutes of moderate exercise per week, such as brisk walking, swimming or cycling.
- Two strength training sessions per week, to preserve muscle mass.
- Seven to eight hours of sleep. Lack of sleep increases hunger and insulin resistance.
Medication and surgery
In selected cases, weight loss medications are used. The newer injectable medications (GLP-1 analogues) must be stopped in good time before trying to conceive, usually at least two months beforehand, according to the instructions for each medication. After bariatric surgery, a wait of about 12 to 18 months before pregnancy is recommended, so that weight and nutrition can stabilize.
Weight, age and time: how to weigh the decision about treatment
Weight loss improves the chances. But the time it takes matters, especially after 35, when ovarian reserve declines every year. A 38-year-old woman who spends two years dieting before starting treatment may lose more than she would gain.
That is why the decision must be individualized:
- For younger women with time on their side, a structured 3 to 6 month program before treatment makes sense.
- At older ages, weight loss can happen alongside treatment, for example by freezing embryos now and transferring them once weight has improved.
- At a very high BMI, the safety of anesthesia and pregnancy requires collaboration with an anesthesiologist and an endocrinologist.
Preparing for a safe pregnancy with higher weight
If your BMI is 30 or higher, a few simple steps before conception reduce the risks for you and your baby:
- Higher-dose folic acid: UK guidelines (RCOG) recommend 5 mg a day instead of 400 μg, starting at least one month before conception. Your doctor will set the dose.
- Vitamin D: women with higher weight are more often deficient.
- Blood sugar and blood pressure checks: before pregnancy and early in pregnancy.
- Thyroid: thyroid disorders affect both weight and fertility.
- Planning your monitoring: during pregnancy, prenatal screening and ultrasounds may need adjustments, because abdominal fat makes imaging more difficult.
Myths about weight and fertility
- “I have to reach my ideal weight to get pregnant.” No. Even moderate weight loss, far from the ideal, often improves ovulation and response to treatment.
- “Since I get my period every month, my weight does not affect me.” A regular cycle is a good sign, but it does not rule out an effect on egg quality and the endometrium.
- “A strict diet for a few weeks will solve the problem.” Rapid weight loss can disrupt your cycle and lead to nutrient deficiencies just before conception. Steady, gradual weight loss is safer.
- “Obesity only concerns the woman.” As we saw, it also affects sperm quality.
Very low weight also affects fertility
The discussion about weight is not only about extra kilos. When BMI drops below 18.5, or when a woman exercises very intensely without eating enough, the body goes into energy-saving mode. The hypothalamus reduces its signals to the ovaries, and periods become infrequent or stop. This condition is called hypothalamic amenorrhea.
- Treatment is based mainly on increasing energy intake and reducing intense exercise.
- It often requires working with a dietitian and, where there is an eating disorder, with a mental health professional.
- Pregnancy at a very low weight is linked to lower birth weight and preterm birth, so restoring weight before conception benefits the baby too.
Whether weight is high or low, the goal is the same: a body in balance that can support ovulation and a healthy pregnancy.
What you gain from moderate weight loss
Losing 5% to 10% of your starting weight seems small. For a woman weighing 90 kg, it means 5 to 9 kg. But the benefits are often disproportionately large:
- Return of spontaneous ovulation in many women with infrequent or absent cycles.
- Better response to ovulation induction medications, often at lower doses.
- Improved insulin sensitivity and blood lipids.
- Lower risk of gestational diabetes and high blood pressure in pregnancy.
- Better mood, sleep and energy, which help you get through the process.
Every kilo counts. You do not need to wait until you reach your final goal to discuss the next step with your doctor.
Frequently Asked Questions
How does obesity affect a woman's fertility?
It disrupts the hormones that regulate ovulation, increases insulin resistance and is associated with polycystic ovaries. The result is infrequent cycles and lower chances of conception.
Is male fertility affected too?
Yes. Excess weight lowers testosterone and can reduce sperm count and motility.
How much weight do I need to lose to see a difference?
Losing 5 to 10% of body weight is often enough to restore ovulation and improve response to treatment.
Does obesity reduce IVF success?
Higher doses of medication are usually needed, egg retrieval is technically more difficult and pregnancy rates are slightly lower, while the risk of miscarriage increases. Read more about in vitro fertilization.
What are the risks in pregnancy?
Higher rates of gestational diabetes, hypertension, preeclampsia and cesarean section. Losing weight before conception reduces these risks.
What BMI is considered safe for IVF?
There is no single limit that applies to everyone. Risks increase gradually as BMI rises, especially above 35 to 40. The decision is made on an individual basis, depending on age, medical history and the anesthesiologist's assessment.
Does metformin help with fertility?
In women with polycystic ovaries and insulin resistance, it can improve how often ovulation occurs, mainly when combined with lifestyle changes. It is not a weight loss drug and is given only on medical advice.
Can I get pregnant while taking weight loss injections?
GLP-1 analogues are not recommended during pregnancy. If you are thinking about conceiving, discuss with your doctor when to stop them, usually at least two months beforehand. Some of them may also affect the absorption of birth control pills.
Does my partner need to lose weight too?
If he is overweight, yes. Weight loss improves hormones and sperm quality, and a shared effort makes the changes easier for the couple.
