Obesity is a global health issue that affects millions of people worldwide. In addition to its well-known impact on general health—such as an increased risk of cardiovascular disease, diabetes, and certain types of cancer—obesity also has a significant effect on reproductive health in both men and women.
- Obesity can affect fertility in both men and women.
- In men, a high BMI can impact sperm quality and embryonic development.
- Recent studies have shown an increased risk of miscarriage when the male partner has obesity.
- In women, obesity can reduce egg quality, implantation rates, and IVF success rates.
- It also increases the risk of complications during pregnancy.
- The weight of both partners influences reproductive outcomes.
The impact of male obesity on fertility
While the effects of female obesity on fertility have been widely studied, the impact of male obesity has received less attention. However, this study shows that a high BMI in men can negatively influence early embryonic development and increase the risk of miscarriage.
Researchers analyzed more than 7,800 embryos from 1,398 intracytoplasmic sperm injection (ICSI) cycles in egg donation treatments. They found that embryos from obese men showed delayed development during the early stages of cell division. In addition, blastocysts derived from these embryos had lower inner cell mass quality, which could affect their ability to develop properly.
Although fertilization and blastocyst formation rates were similar across normal-weight, overweight, and obese men, implantation and clinical pregnancy rates were slightly lower in couples where the male partner was obese. Most concerningly, miscarriage rates were significantly higher in these couples, suggesting that male obesity may have cumulative effects on embryo viability and subsequent development.
Why does male obesity affect sperm?
Male obesity can affect fertility and reproductive outcomes through several mechanisms. For example, men with a high BMI tend to have poorer sperm quality, including lower semen volume (hypospermia), reduced sperm concentration (oligozoospermia), decreased sperm motility (asthenozoospermia), and increased sperm DNA fragmentation. These factors can compromise the genetic integrity of sperm, which in turn may affect embryonic development and increase the risk of chromosomal abnormalities that could lead to miscarriage.
Additionally, male obesity can cause hormonal imbalances, such as elevated estrogen levels and reduced testosterone, which negatively impact sperm production and quality. Excess body fat—particularly in areas such as the abdomen and thighs— can also increase scrotal temperature, impairing spermatogenesis and sperm quality.
How does female obesity influence fertility?
Female obesity also has a significant impact on reproductive outcomes, both in natural conception and assisted reproduction treatments. Women with a high BMI often experience a reduced ovarian response, lower egg and embryo quality, and impaired endometrial receptivity. These factors contribute to lower success rates in in vitro fertilization (IVF) treatments and a higher risk of pregnancy complications such as preeclampsia, gestational diabetes, and preterm birth.
In addition, obese women have a higher risk of miscarriage, even when euploid embryos (with a normal number of chromosomes) are transferred. This suggests that obesity may negatively affect the uterine environment, making implantation and embryo development more difficult. Chronic inflammation, oxidative stress, and metabolic disturbances are among the mechanisms proposed to explain these effects.
The importance of addressing obesity in both partners
The findings of this study conducted at Eugin, along with others, highlight the importance of considering the BMI of both partners when planning assisted reproduction treatments. Obesity not only affects egg and sperm quality but can also influence embryonic development and increase the risk of complications during pregnancy.
Therefore, it is essential for couples trying to conceive—especially those undergoing fertility treatments—to consider weight loss as a strategy to improve their chances of success.
Healthcare professionals should include weight management as an integral part of reproductive care, providing guidance on nutrition, physical activity, and lifestyle changes. It is also important for patients to understand that obesity affects not only their general health but also their ability to conceive and carry a healthy pregnancy to term.
Would you like to understand how this may affect you?
If you are trying to conceive and are concerned about how weight may be affecting your fertility, a medical consultation can help clarify your situation and provide personalized guidance.
At Eugin, we offer a free initial consultation, where our team will assess your case and, if necessary, guide you on the most appropriate tests or treatments for you.
Written by Dr. Rafael Lafuente, Head of the Andrology Laboratory at Eugin Barcelona
