Can Being Overweight or Underweight Affect Fertility?

Key Takeaways

• Both being overweight and being underweight can disrupt hormones and reduce the chances of conception

• In women, excess weight is linked to irregular periods, PCOS, and anovulation (no egg release)

• In men, obesity reduces testosterone, lowers sperm count and motility, and increases sperm DNA damage

• Being underweight can cause hypothalamic amenorrhoea, where the brain switches off the reproductive cycle

• A 5–10% change in body weight can restore ovulation and improve sperm quality

• Both partners' weight matters; male factor infertility accounts for 40–50% of all fertility challenges

When you're trying to conceive, your body weight and your partner's can play a significant role in whether and how quickly you get pregnant. Weight affects the hormones that drive ovulation and sperm production in ways that are well-documented and, importantly, often reversible. 

Does Weight Affect Female Fertility?

Yes, at both extremes, body weight disrupts the hormonal balance needed for regular ovulation.

Fat tissue (adipose tissue) is not just passive storage. It actively produces and regulates oestrogen, the hormone that drives the menstrual cycle. When body fat is significantly too high or too low, oestrogen balance is disrupted, and ovulation can become irregular, delayed, or stop entirely.

Can Being Overweight Stop You From Ovulating?

Yes, it can. According to the American Society for Reproductive Medicine (ASRM), 30–36% of women with obesity experience menstrual cycle irregularities, and ovulatory dysfunction is significantly more common at higher body weights.

Excess weight, particularly abdominal fat, leads to:

• Elevated oestrogen levels that disrupt the hormonal signals triggering ovulation

• Insulin resistance, which further suppresses ovulation and is a key driver of PCOS

• Anovulation cycles where no egg is released, reducing the monthly chance of conception

• Irregular periods make it harder to identify your fertile window or know when to take a pregnancy test

Also read: How Soon Can You Take a Pregnancy Test? 

Can Being Underweight Affect Ovulation?

Yes. Research published in Fertility and Sterility confirms that chronic energy deficiency disrupts the hypothalamic-pituitary-gonadal (HPG) axis, causing hypothalamic anovulation, where the brain essentially pauses the reproductive cycle to conserve energy.

Being significantly underweight can cause:

• Hypothalamic amenorrhoea, the loss of periods, is common in athletes and those with very low body fat

• Absent or infrequent ovulation, reducing your conception window per year

• Lower progesterone affects the uterine lining and the body's ability to sustain early pregnancy

• Irregular cycles make timing intercourse and pregnancy testing extremely difficult

Does Weight Affect Male Fertility?

Yes, and this is one of the most under-discussed aspects of the TTC journey.

Male factor infertility accounts for roughly 40–50% of all fertility challenges in couples. Excess body weight affects male reproductive health through several well-researched biological pathways.

How Does Excess Weight Reduce Sperm Quality?

Testosterone converts to estrogen in fat tissue. Adipose tissue contains an enzyme called aromatase that converts testosterone into estrogen. According to NIH-published research, this is the primary mechanism by which obesity impairs male fertility: elevated estrogen suppresses the hormonal axis that drives sperm production, lowering testosterone and reducing sperm development.

The reproductive consequences are measurable:

• Lower sperm count and concentration research in Human Reproduction Update found that infertility rates are approximately 50% higher in men with obesity than in men of healthy weight

• Reduced sperm motility and morphology, affecting the sperm's ability to reach and fertilise an egg

• Increased sperm DNA fragmentation: NIH-published studies confirm higher DNA damage in sperm from men with obesity, which can reduce fertilisation rates and increase early pregnancy loss risk even when conception occurs

• Elevated scrotal temperature: excess fat around the groin raises testicular temperature, and as confirmed by PMC research, even small increases in scrotal heat impair sperm development

Can Being Underweight Affect Male Fertility Too?

Yes. Very low body fat reduces testosterone production, lowers sperm counts, and decreases libido. Men who over-exercise or follow highly restrictive diets are particularly at risk of these hormonal disruptions.

Also read: How Accurate Are Early Pregnancy Tests Before a Missed Period? 

What Can You Do About It?

Small, sustainable changes make a measurable difference.

Multiple NIH-funded studies show that a 5–10% change in body weight, in either direction, for those significantly over or underweight, can restore ovulation, improve hormone balance, and enhance sperm parameters. You do not need to reach an idealized number before progress begins.

Steps worth taking together:

1. See your doctor, both of you. A GP or reproductive specialist can assess hormone levels, run semen analysis, evaluate cycle regularity, and screen for PCOS, thyroid issues, or insulin resistance. This applies to both partners equally.

2. Track ovulation carefully. If weight-related hormonal changes are making your cycles irregular, use ovulation predictor kits (OPKs) and basal body temperature (BBT) tracking rather than relying on period dates alone.

3. Test at the right time. If your cycles are irregular, base your testing on ovulation, not your last period. Test at least 12–14 days after ovulation. Using an early pregnancy detection test with high hCG sensitivity gives you the most accurate result as early as possible, reducing the guesswork during an already anxious wait.

4. Focus on nourishment, not punishment. Sustainable, whole-food dietary changes and moderate movement consistently outperform crash diets or extreme exercise for restoring hormonal health.

Frequently Asked Questions

Can I still get pregnant if I'm overweight? 

Yes. Being overweight reduces the likelihood of regular ovulation and can lengthen the time to conception, but many people conceive with no difficulty at higher body weights. If you've been trying for 6–12 months without success, see a doctor.

How quickly can weight loss improve fertility? 

Research shows that ovulation can resume and hormonal balance can improve within a few months of modest weight loss. A 5–10% reduction in body weight is associated with meaningful improvements in both ovulation regularity and conception rates.

Does my partner's weight affect our chances of conceiving? 

Yes. Male obesity is linked to lower sperm count, reduced motility, higher DNA fragmentation, and hormonal disruption. Both partners' reproductive health matters equally.

Can being underweight prevent pregnancy? 

Yes, very low body weight can cause hypothalamic amenorrhea, where ovulation stops entirely. Restoring adequate nutrition and energy availability can restart ovulation, often without medical intervention.

When should I take a pregnancy test if my cycles are irregular due to weight? 

Always test based on ovulation timing, not period dates. Use an early pregnancy detection test at least 12–14 days after you believe you ovulated, using first morning urine, for the most accurate result. Retest after 48–72 hours if the first result is negative.

The Bottom Line

Weight affects fertility in both men and women through hormonal disruption, irregular ovulation, and reduced sperm quality. But it is one factor among many and one of the most addressable ones. With the right medical support and targeted lifestyle changes, many couples navigate these challenges and go on to conceive.

Stay informed, look after each other, and track your cycle carefully. When the moment arrives, our early pregnancy detection test strips are designed to give you the earliest, most accurate answer possible.

References:

• https://www.asrm.org/practice-guidance/practice-committee-documents/obesity-and-reproduction-a-committee-opinion-2021/
  
• https://pmc.ncbi.nlm.nih.gov/articles/PMC7457958/
• https://pmc.ncbi.nlm.nih.gov/articles/PMC4408383/
• https://pmc.ncbi.nlm.nih.gov/articles/PMC3521747/ 
• https://pmc.ncbi.nlm.nih.gov/articles/PMC5798797/
• https://academic.oup.com/humupd/advance-article/doi/10.1093/humupd/dmaf025/8279592
• https://www.sciencedirect.com/science/article/abs/pii/S0026049520300937
• https://www.aafp.org/pubs/afp/issues/2019/0701/p39.html