Conversations about health and fertility can be deeply personal, especially when they touch on weight. We understand how emotional this topic can be—our aim isn’t to blame or shame, but to share knowledge that empowers you. What’s most important is supporting your metabolic health, as it plays a central role in your reproductive wellbeing.
First, we want to say that being very overweight or obese doesn’t mean you will have fertility issues. The interactions between obesity and infertility are complex, and the information available can seem confusing and even conflicting. If you have been ‘large’ all your life, come from a family of bigger-than-average people, eat healthily, and exercise, then you probably don’t have to worry. Most of us can point to a friend or relative who would have a high BMI but who has had no problems conceiving.
However, many other women (and men) who carry additional weight have trouble conceiving. Reproduction is intricately linked to energy balance via several hormones and cellular interactions, so getting that balance right can help with fertility.
Excess weight itself doesn’t directly cause infertility. Rather, the underlying factors that contribute to weight gain—such as hormonal imbalances, insulin resistance, and inflammation—can affect reproductive health. Being very overweight and having fertility issues are both outcomes of unbalanced hormones. So, when we talk about “obesity-related infertility” we mean exactly that – obesity and fertility are linked, but your weight isn’t causing your infertility.
Studies show that people with poor metabolic health are more likely to experience irregular periods, ovulatory issues, reduced IVF success, and higher miscarriage risk. Improving metabolic markers, even without dramatic weight loss, can significantly enhance reproductive outcomes.
Those most at risk of obesity-related infertility tend to have been of regular weight when young and then had rapid weight gain after puberty or in early adult life. Obesity acquired in adulthood tends to be visceral fat (the fat that is around your middle and internal organs), which is more metabolically active and which also induces inflammation in the body.
Adult weight (and the number of fat cells you have) in most situations is genetically determined. When we put on a large amount of weight, these fat cells enlarge in size. The resulting stretch of the fat cells causes the release of a number of pro-inflammatory signals (called adipokines) which influence the metabolism and also interfere with ovarian and reproductive function.
Insulin resistance driven by this pro-inflammatory state adds to the mix. Several studies have shown an association of this pro-inflammatory visceral fat with ovulation, embryo function, implantation, and overall pregnancy outcomes.
Adipose tissue (ie fat cells) produces many hormones, including:
Polycystic ovarian syndrome (PCOS) is a common reproductive condition tied to metabolic dysfunction, especially insulin resistance. While it often occurs alongside higher body weight, it is fundamentally a hormonal disorder. The ‘cysts’ in PCOS aren’t the cause of fertility issues; rather, they are the result of a complex set of hormonal interactions gone awry that can cause infertility.
PCOS is characterised by abnormal ovarian function due to insulin resistance and increased androgens (male hormones) in the blood. Obesity increases the risk of PCOS as the fat cells expand and excrete hormones which leads to a hormonal imbalance that disrupts the normal functioning of the ovaries.
These unbalanced hormones interfere with the development of ovarian follicles and timely ovulation causing delayed or irregular cycles, multiple ovarian cysts, and sometimes acne and unwanted facial and body hair growth. Additionally, women with PCOS have a higher risk of miscarriage and are more likely to develop gestational diabetes during pregnancy.
Improving metabolic health—through insulin-sensitising strategies—can make a major difference in managing PCOS and enhancing fertility.
Certain fertility procedures, like egg collection, may carry added risk when metabolic health is poor—especially if this leads to higher BMI. At Flinders Fertility, procedures are performed at Glenelg Day Surgery, which has safety thresholds to ensure the best outcomes. In cases where additional support is needed, we can refer you to clinics affiliated with Ashford or St Andrew’s hospitals.
These protocols aren’t about judgment—they’re about safety. Metabolic health impacts everything from anesthesia response to healing and recovery.
To be able to produce healthy sperm, the testes have to be cooler than normal body temperature at around 34-35C. It is common for men with obesity to have an excess of abdominal, inner thigh, and pubic area fat which can increase the scrotal temperature and inhibit the production of sperm2.
Additionally, increased temperature leads to DNA fragmentation and increased oxidative stress which in turn changes semen parameters and function resulting in infertility.
If you're looking for support to improve your metabolic health before conception, we recommend the Flinders Fertility Metabolic Reset Program.
This structured 3-month program is designed specifically for individuals with a BMI over 30 who are preparing for fertility treatment. It combines:
An initial appointment with a fertility doctor, your fertility goals, and ordering blood tests
*GLP-1 medication (e.g., Semaglutide) if required
Weight and symptom tracking
Regular Nurse check-ins
Weekly educational content on diet, exercise, protein intake, and psychosocial health
The program focuses on restoring hormonal balance and reducing inflammation—not crash dieting—so you can optimize your body for conception in a safe, supported way.
The goal isn’t rapid weight loss, but restoring healthy hormonal function. The first 1000 days—from pre-conception through toddlerhood—are crucial for setting the metabolic tone for your future child. We recommend seeing a fertility dietitian for support. The Early Life Nutrition Alliance is a global group of fertility dietitians with a large member base in Australia. They offer telehealth consultations and can give you the extra support you may need. Check out their website to book an appointment.
Together, we’ll explore the root causes—whether they’re hormonal, metabolic, or both—and create a plan that works for your body and your goals.
References
1. Adolescent body mass index and infertility caused by ovulatory disorders.
J W Rich-Edwards 1, M B Goldman, W C Willett, D J Hunter, M J Stampfer, G A Colditz, J E Manson in pubmed.ncbi.nlm.nih.gov/8030695/
2. Obesity, An Enemy of Male Fertility: A Mini Review.
Mohamed Ahmed Abd El Salam in Oman Medical Journal [2018], Vol. 33, No. 1: 3-6
Clinical Review by Associate Professor Vasant Shenoy