The link between body weight and fertility

Many women don’t realize they have a fertility issue until they try to get pregnant, but that longed-for positive pregnancy test doesn’t happen. Fertility testing can give you the answers you need, but it’s also important to know that maintaining a healthy weight can have a big impact on your ability to conceive. Studies have shown a clear link between body weight and fertility in women. Obesity and infertility can be connected, but being underweight can cause fertility problems, too.

What’s the link between obesity and infertility?

Ovulation plays a critical role in getting pregnant. In healthy women of reproductive age, the ovaries will typically produce one egg in each menstrual cycle, which can then be fertilized by sperm inside the fallopian tubes, creating an embryo that can implant in the uterus and grow into a fetus.

When a woman is overweight, excess fat cells can cause hormone problems that disrupt that clockwork cycle of ovulation. That’s because extra fat cells produce estrogen, which mimics the effect of hormonal birth control and interferes with the ovaries’ ability to produce eggs each month.

Some women who are overweight develop a condition known as polycystic ovary syndrome, or PCOS, which is a common cause of infertility. This hormone disorder also interferes with ovulation, as women with PCOS often have high androgen levels, insulin resistance, and numerous ovarian cysts rather than mature eggs to ovulate.

While fertility treatment can often overcome problems with weight and fertility, it’s important to know that obesity lowers the success rates of fertility treatments, including IVF, and increases the chances of a pregnancy ending in miscarriage. Being overweight can also increase the chances of pregnancy complications, including gestational hypertension and gestational diabetes. Losing weight can increase your chances of success, whether you try to conceive naturally or with treatment.

Women aren’t the only ones in whom obesity and infertility are linked. For men, extra weight can disrupt testosterone levels, which can have negative effects on sperm.

Can being underweight affect fertility?

Just as having too many fat cells can cause infertility, having too few can also be problematic. In women whose BMI is 18.5 or lower, natural body fat is very low, which causes estrogen levels to drop. A lack of estrogen can cause ovulation to become irregular or stop altogether, a condition called amenorrhea.

Women who are underweight also have a higher risk of premature birth and low-birth-weight infants, so maintaining a healthy weight during pregnancy is also important.

While many women believe that exercise and dieting are the keys to health, the truth is that when you’re trying to get pregnant, the goal should be to achieve a healthy weight. Extreme exercise and restrictive dieting can cause problems with weight and fertility, so we advise our patients to eat a healthy diet and enjoy moderate exercise while trying to conceive.

What’s the ideal BMI window for fertility?

Generally speaking, a BMI between 18.5 and 24.9 is considered an ideal weight range to create the balanced hormone environment needed to support regular ovulation.  

If you are struggling to conceive, working toward achieving a healthy weight is always a good start. However, there are many causes of infertility beyond being over- or underweight, so we encourage all women to seek out fertility testing if they have been trying to conceive for a year or longer. In women ages 35 or older, it’s smart to get tested after just six months of trying.

We are here to help you have the family you dream of. If you have concerns about weight and fertility, contact us to schedule an appointment with Andrew Levi, MD, at our Connecticut fertility center.

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