Does Weight Affect Fertility?

There is a relationship between body weight and fertility in both women and men. Maintaining an appropriate weight will influence the chances of pregnancy and, therefore, the success of assisted reproduction treatment, if applicable.

That is why it is very important to follow a balanced diet at all times.

What is the ideal weight to get pregnant?

There is no single weight considered “ideal” for becoming pregnant, since appropriate weight can vary according to several factors such as height, body composition, and overall health. Rather than focusing only on weight, healthcare professionals usually use the Body Mass Index (BMI) as a more comprehensive measure. Weight and pregnancy can be assessed this way.

What effects can overweight have on female fertility?

Some consequences of obesity or overweight in women include a higher likelihood of:

• Cardiovascular problems, hypertension
• Hormonal issues that can disrupt ovulation and produce benign tumors in the ovaries and uterus (due to increased estrogens)
• PCOS (polycystic ovary syndrome), one of the conditions that can hinder fertility
• Type II diabetes and insulin resistance (which also affects fertility)
• Pregnancy pathologies such as gestational diabetes, preeclampsia, miscarriage, newborns with abnormal birth weight
• Altered quality and quantity of oocytes in Assisted Reproduction treatments

In addition, women with overweight undergoing in vitro fertilization (IVF) will require higher doses of gonadotropins to stimulate oocyte production. Increased medication carries a higher risk of side effects, as well as a higher financial cost of assisted reproduction treatment for the patient.

And what about being underweight?

A weight below normal can also be harmful to fertility.

According to the WHO, a normal weight corresponds to a BMI between 18.5 and 24.9. Therefore, a BMI below 18.5 is considered underweight. Values below 16 indicate extreme thinness.

Fertility problems in underweight women: a low body fat level—whether due to a strict diet or excessive exercise—directly affects the hormones that regulate the menstrual cycle, and its consequences may include:

• During puberty, a delay in sexual maturation
• In adult women, ovulatory disorders or even complete interruption of ovulation with absence of menstruation (amenorrhea)
• Alteration of the inner lining of the uterus, directly affecting possible embryo implantation
• Underweight during pregnancy has also been linked to a higher probability of preterm birth and low birth weight

It is estimated that the ideal BMI when becoming pregnant should be between 20 and 22.

How does weight affect male fertility?

Body weight also affects male fertility. In cases of overweight or obesity in men:

• Decreased ejaculate volume (oligospermia)
• Reduced testosterone levels, affecting sexual activity or erectile function
• Decrease in sperm count, even leading to absence of sperm (azoospermia)
• Increased testicular temperature, which results in lower sperm motility

Being underweight in men can also influence sperm count and activity, although there are fewer studies on this.

Do you have any questions or need more information?

At Fertility Madrid, we specialise in treatments such as egg donation, in vitro fertilisation and artificial insemination, among others.

Please do not hesitate to contact our professionals at our fertility clinic and they will answer all your questions without obligation.