How weight impacts your chances of getting pregnant

pregnancyweight — Being underweight or overweight can affect your fertility and your pregnancy.
Tetra Images/ Getty Images

Having a body mass index (BMI) that is too high or too low can impact your ability to conceive.
If you are overweight or obese, losing weight can boost fertility and increase the chances of getting pregnant.
Weight is closely linked to underlying fertility issues in both men and women.
Visit Insider’s Health Reference library for more advice.

If you are trying to conceive, maintaining a healthy weight can help increase your chances of getting pregnant.

Having a body mass index (BMI) that is too high (>25) or too low (<18) can impact your ability to conceive and increase complications during pregnancy, says Emily Osman, MD, an OB-GYN and reproductive endocrinologist with the RMA network in New Jersey.

“Weight is closely linked to underlying fertility issues in both men and women,” Osman says, adding that an unhealthy weight can also “reduce the chances of fertility treatments being successful.”

Find out more about how weight affects fertility, and what you can do about it.

How weight affects fertility

About 12% of female infertility may be connected to the patient’s weight being too high or too low, according to the American Society of Reproductive Medicine (ASRM).

"For women, being underweight or overweight may be associated with what's known as ovulatory dysfunction, or the ability to regularly release an egg in order to conceive," Osman says.

For those who are among the 74% of overweight or obese Americans, a moderate weight loss of 7% and an increase in activity can improve fertility, says Osman's colleague, Jason Franasiak, MD, an infertility specialist.

That's because body fat affects hormones, including those needed to mature and release an egg.

Underweight women may stop releasing gonadotropin-releasing hormone (GnRH), which leads to a condition known as hypothalamic amenorrhea, where there is no menstrual cycle, no egg release, and therefore no egg to fertilize.

Overweight individuals are more likely to have higher estrogen levels. In females, high estrogen levels can shut down the menstrual cycle, again leaving no egg to be fertilized. In males, higher estrogen levels can impact testicular function, leading to lower sperm count and, thus, decreased chances for a sperm to fertilize an egg.

Overweight females are also at a higher risk for physical conditions including polycystic ovary syndrome (PCOS), tubal infections, and endometriosis, all of which can make it more difficult to conceive and carry a pregnancy to term.

How weight affects pregnancy health

In addition to impacting fertility, weight can also affect the outcome of pregnancy. "Maternal obesity is strongly associated with mom and baby complications," says Franasiak.

Being underweight or overweight brings its own set of risks:

Being underweight is linked to complications such as preterm labor and low birth weight.
Being overweight increases the risk of almost all pregnancy complications, including miscarriage, high blood pressure and pre-eclampsia.

Obesity-related complications in pregnancy

Miscarriage and stillbirth: Obese (BMI >30) pregnant people have a roughly 20% increased risk for first-trimester miscarriages and are three times more likely to experience recurring miscarriages than those with a healthy BMI. The risk for stillbirth also increases with higher BMI.
Gestational diabetes: Overweight (BMI 25-29.9) and obese (BMI >30) pregnant people have an increased risk for gestational diabetes. Their collective risk accounts for roughly half of gestational diabetes cases. In turn, gestational diabetes increases risks for other pregnancy complications including high blood pressure, birth injuries to the baby and mother, and stillbirth.
Birth defects: Overweight pregnant mothers are more likely to have children with heart or neural tube defects, such as spina bifida, and are more likely to give birth prematurely, which comes with a host of lifelong health risks for the baby.

How does losing weight increase fertility?

It's a good idea to try to get your body weight closer to a healthy range before trying to conceive, Franasiak says. However, if your BMI is much higher than 24.9, even small changes can boost your fertility and lead to a healthier pregnancy.

"Current recommendations include a weight loss of 7% of body weight and increased weekly physical activity of at least 150 minutes - or 30 minutes in 5 out of 7 days - which can be as simple as walking," Fransiak says.

Eating healthy and moving regularly can help you achieve moderate weight loss, Fransiak says. Ask your doctor for a referral to a nutritionist who can help support weight loss or gain; doing so may increase your chances of conception and healthy pregnancy.

If your doctor diagnoses insulin resistance or PCOS, they might prescribe a medication like metformin, but there are no weight-loss drugs that are commonly used for people trying to conceive since weight loss medications are not recommended for those trying to have a baby.

People who are very overweight and have struggled to lose weight may also consider surgical weight-loss options, but should not try to get pregnant for at least a year after surgery, Fransiak says.

Insider's takeaway

Weight can impact conception for both males and females, and it can affect pregnancy health for mother and child.

It is possible to conceive and have a healthy pregnancy if you are overweight or obese. However having a BMI of less than 18.5 or more than 24.9 can affect your hormonal health, affecting fertility and making it difficult to conceive.

For overweight individuals, a small weight loss of 5-7% of body weight can boost your fertility, increase your chances of getting pregnant, and decrease health risks during pregnancy. Your doctor can work with you to put together a plan for healthy weight loss.

"Weight loss can be challenging, but it will help to increase the likelihood of conception and a healthy pregnancy," Osman says.