From the Guidelines
A healthy BMI range for optimal fertility is generally between 18.5 and 24.9, as supported by the most recent evidence 1.
Importance of BMI for Fertility
This range is crucial because women with BMIs below 18.5 (underweight) may experience irregular menstrual cycles or amenorrhea due to insufficient body fat needed for normal hormone production.
- Conversely, women with BMIs above 30 (obese) often face fertility challenges including irregular ovulation, decreased conception rates, and increased risk of pregnancy complications.
- For men, obesity can reduce sperm quality and quantity, further complicating fertility issues.
Impact of BMI on Fertility Outcomes
Weight management through balanced nutrition and regular exercise is recommended for those outside the optimal range.
- Even modest weight loss of 5-10% in overweight individuals can significantly improve fertility outcomes, as it helps in achieving a healthier BMI range.
- The connection between BMI and fertility stems from how body fat affects hormone production and regulation, particularly estrogen, progesterone, and testosterone, which are crucial for reproductive function.
Clinical Recommendations
Maintaining a healthy weight supports proper hormone balance and reproductive health for both partners trying to conceive.
- According to the Endocrine Society, women with Functional Hypothalamic Amenorrhea (FHA) should have a BMI higher or equal to 18.5 kg/m2 before ovulation induction is offered 1.
- This guideline emphasizes the importance of achieving and maintaining a healthy BMI for optimal fertility outcomes, aligning with the general recommendation for a BMI range of 18.5 to 24.9.
From the Research
BMI and Fertility
- The relationship between Body Mass Index (BMI) and fertility is complex, with studies suggesting a J-shaped or U-shaped association between the two 2, 3.
- High BMI in both women and men is associated with subfertility, while low BMI also increases the risk of subfertility 2, 4.
- A BMI between 20 and 25 kg/m2 is considered optimal for minimal risk of subfertility 2.
Optimal BMI Range for Fertility
- Studies suggest that a BMI of 23-25 kg/m2 is associated with the lowest risk of subfertility in women and men, respectively 2.
- Women with a BMI ≥25 are less likely to attain clinical pregnancy, with a further decrease in likelihood for those with a BMI ≥30 5.
- A BMI <20 kg/m2 is also associated with an increased risk of subfertility, highlighting the importance of maintaining a healthy weight for optimal fertility 2, 3.
Impact of BMI on Fertility Treatment
- Being overweight or obese can negatively impact assisted reproductive technology (ART) outcomes, including reduced clinical pregnancy rates and longer duration of stimulation 5.
- Some studies suggest that BMI restrictions may be necessary for fertility treatment, with the majority of reproductive endocrinology and infertility (REI) and maternal-fetal medicine (MFM) subspecialists agreeing on upper limit BMI cutoffs 6.