Infertility treatment for obese women requires a tailored approach that addresses both reproductive challenges and metabolic health. Obesity, defined as a BMI of 30 kg/m² or above, can disrupt ovulation, reduce fertility treatment success rates, and increase pregnancy risks. However, evidence shows that even modest weight loss of 5–10% can restore ovulatory function and improve conception outcomes. Treatment options range from lifestyle modification and ovulation induction to assisted reproductive technologies, though NHS eligibility often depends on meeting BMI criteria. This article explores how obesity affects fertility, evidence-based weight management strategies, available fertility treatments, and how to navigate NHS services whilst managing associated health risks.

How Obesity Affects Fertility in Women

Obesity, defined as a body mass index (BMI) of 30 kg/m² or above, can significantly impact female reproductive health through multiple physiological mechanisms. Excess adipose tissue disrupts the hypothalamic-pituitary-ovarian axis, leading to hormonal imbalances that may impair ovulation. Adipose tissue functions as an endocrine organ, producing oestrogen through the aromatisation of androgens. This excess oestrogen creates a negative feedback loop that can suppress follicle-stimulating hormone (FSH) and luteinising hormone (LH) secretion, which are essential for normal ovulatory cycles.

Many women with obesity experience anovulation or irregular menstrual cycles. Research indicates that higher BMI is associated with reduced natural fecundity and lower success rates with assisted reproductive technologies, though individual outcomes vary considerably. Obesity is also strongly associated with polycystic ovary syndrome (PCOS), a leading cause of anovulatory infertility. Around 50–70% of women with PCOS have overweight or obesity. The condition creates a cycle of insulin resistance, hyperinsulinaemia, and hyperandrogenism that can further compromise ovarian function.

Beyond ovulatory dysfunction, obesity may affect endometrial receptivity and early embryo development. The inflammatory state associated with excess adiposity may impair implantation, whilst altered metabolic parameters can affect oocyte quality. Studies demonstrate that women with obesity have lower success rates with assisted reproductive technologies, including in vitro fertilisation (IVF), with reduced implantation rates and increased risk of early pregnancy loss.

It is important to note that many women with obesity conceive without difficulty; however, the risks of infertility and pregnancy complications increase with higher BMI.

Key impacts of obesity on fertility include:

• Disrupted ovulation and menstrual irregularity

• Increased risk of PCOS and insulin resistance

• Reduced oocyte quality and endometrial receptivity

• Higher rates of early pregnancy loss

• Decreased success with fertility treatments

Weight Loss and Fertility: Evidence-Based Approaches

Weight reduction represents the most effective first-line intervention for improving fertility outcomes in women with obesity, with evidence demonstrating that even modest weight loss of 5–10% of body weight can restore ovulatory function and improve conception rates. NICE advises weight reduction to improve chances of conception and treatment outcomes; local NHS Integrated Care Boards (ICBs) may set BMI criteria for funded access to fertility treatments. Weight optimisation before conception also enhances maternal and foetal safety during pregnancy.

Structured lifestyle modification programmes combining dietary intervention, increased physical activity, and behavioural support form the cornerstone of evidence-based weight management. A calorie-controlled diet creating a deficit of 500–600 kcal per day, alongside 150 minutes of moderate-intensity exercise weekly, can achieve sustainable weight loss. Studies show that women who lose 5–10% of their body weight experience significant improvements in menstrual regularity, with many anovulatory women resuming ovulation. This often results in spontaneous conception without the need for medical intervention.

For women with a BMI above 35 kg/m² who have not achieved adequate weight loss through lifestyle measures, pharmacological interventions may be considered under specialist supervision. Orlistat, a lipase inhibitor that reduces dietary fat absorption, is licensed for weight management in the UK and may be prescribed alongside lifestyle modification. Women taking orlistat should consider a daily multivitamin taken at bedtime, at least two hours after orlistat, to ensure adequate fat-soluble vitamin intake. Orlistat should be stopped immediately if pregnancy occurs.

GLP-1 receptor agonists (such as semaglutide [Wegovy] or liraglutide [Saxenda]) and naltrexone/bupropion (Mysimba) are also licensed for weight management in the UK. These medicines are contraindicated in pregnancy and must be stopped before attempting to conceive. For semaglutide, discontinuation at least two months before planned conception is advised. Women should seek specialist advice regarding stopping intervals and use effective contraception during treatment. If pregnancy occurs whilst taking any weight-loss medicine, stop immediately and contact your GP or specialist.

Bariatric surgery represents an option for women with severe obesity (BMI ≥40 kg/m² or ≥35 kg/m² with comorbidities) who have not responded to other interventions. Procedures such as gastric bypass or sleeve gastrectomy can achieve substantial weight loss and dramatic improvements in fertility. However, effective contraception should be used until weight stabilises, typically 12–18 months post-surgery, to allow for nutritional optimisation. Women should receive preconception counselling regarding nutritional supplementation, particularly folic acid (5 mg daily for women with BMI ≥30 kg/m²), vitamin B12, iron, and vitamin D (10 micrograms daily). Ongoing nutritional monitoring and supplementation plans are essential after bariatric surgery.

Fertility Treatment Options for Women with Obesity

When lifestyle interventions alone do not result in conception, various fertility treatments may be considered, though their efficacy and safety profile can be affected by obesity. The choice of treatment depends on the underlying cause of infertility, the degree of obesity, and associated comorbidities.

Ovulation induction with medications such as clomifene citrate or letrozole represents the first-line pharmacological approach for women with anovulatory infertility, including those with PCOS. Clomifene citrate, a selective oestrogen receptor modulator, stimulates FSH release to promote follicular development. However, women with obesity may require higher doses and demonstrate lower response rates compared to women with normal BMI.

Letrozole, an aromatase inhibitor, is recommended as first-line therapy for ovulation induction in women with PCOS by the International PCOS Guideline (ESHRE/ASRM), showing superior ovulation and live birth rates compared to clomifene, particularly in women with obesity. Letrozole is used off-label for ovulation induction in the UK; treatment should be prescribed by a specialist with shared decision-making and informed consent. Treatment cycles should be monitored with ultrasound scanning to assess follicular development and minimise the risk of multiple pregnancy.

For women who do not respond to oral ovulation induction agents, gonadotrophin therapy using injectable FSH preparations may be employed. Higher gonadotrophin doses may be needed; dosing is individualised based on monitored ovarian response. This approach requires careful monitoring due to increased risks of ovarian hyperstimulation syndrome (OHSS) and multiple pregnancy.

Assisted reproductive technologies, including IVF and intracytoplasmic sperm injection (ICSI), may be necessary for women with tubal factor infertility, severe male factor infertility, or those who have not conceived with simpler treatments. However, obesity is associated with reduced success rates, requiring higher gonadotrophin doses, longer stimulation periods, and lower oocyte retrieval numbers. The live birth rate per cycle decreases progressively with increasing BMI. Elective single-embryo transfer is recommended to minimise the risk of multiple pregnancy and associated complications.

Metformin, an insulin-sensitising agent, is commonly used off-label in women with PCOS and obesity to improve metabolic parameters. Whilst it does not directly induce ovulation in all women, it may enhance the effectiveness of other fertility treatments and can reduce the risk of OHSS in IVF cycles for women with PCOS. Treatment should be prescribed by a specialist with shared decision-making. Common side effects include gastrointestinal disturbance, which often improves with gradual dose escalation.

NHS Support and Eligibility for Fertility Services

Access to NHS-funded fertility services in England is determined by Integrated Care Boards (ICBs), resulting in geographical variation in eligibility criteria. NICE guidelines recommend that women under 40 years should be offered three full cycles of IVF if they have been trying to conceive for two years through regular unprotected intercourse, or have undergone 12 cycles of artificial insemination. Women aged 40–42 years should be offered one full IVF cycle under specific conditions. NICE also advises earlier referral (after six months of trying to conceive) for women aged 36 years and over.

However, many ICBs impose additional restrictions based on BMI, with most requiring women to have a BMI below 30 kg/m² to access funded fertility treatment. Some ICBs set the threshold at BMI 35 kg/m² or apply a sliding scale of eligibility. These restrictions are implemented due to evidence showing reduced treatment success rates and increased health risks associated with obesity during pregnancy. Women who do not meet BMI criteria are typically advised to achieve weight loss before treatment eligibility is reconsidered.

Funding criteria differ in Scotland, Wales, and Northern Ireland. Women should check their local ICB or health board policies for specific eligibility requirements.

NHS support for weight management includes referral to specialist weight management services, dietetic support, and structured lifestyle programmes. Many fertility clinics operate integrated weight management pathways, providing multidisciplinary support from dietitians, physiotherapists, and psychologists. Women should discuss their individual circumstances with their GP, who can provide referral to appropriate services and advocate for their care.

For women who do not meet NHS eligibility criteria or face long waiting times, private fertility treatment remains an option. Private clinics may have different BMI thresholds, though most maintain upper limits (typically BMI 35–40 kg/m²) due to clinical safety considerations and reduced success rates.

Key points regarding NHS fertility services:

• Eligibility criteria vary by ICB, with most imposing BMI restrictions

• Weight management support should be offered before fertility treatment

• GP referral is the first step in accessing NHS fertility services

• Private treatment options exist but may also have BMI limitations

• Check local ICB or health board policies and HFEA resources for detailed information

Managing Health Risks During Fertility Treatment

Women with obesity undergoing fertility treatment face elevated risks that require careful clinical management and monitoring throughout the treatment journey and subsequent pregnancy. A comprehensive risk assessment should be undertaken before commencing treatment, addressing cardiovascular health, metabolic status, and potential obstetric complications.

Ovarian hyperstimulation syndrome (OHSS) represents a potentially serious complication of ovulation induction and IVF, characterised by enlarged ovaries and fluid accumulation. Whilst obesity itself may not directly increase OHSS risk, women with PCOS and obesity are at higher risk due to their tendency to produce multiple follicles. Symptoms include abdominal bloating, nausea, rapid weight gain, and reduced urine output. Severe OHSS can cause thromboembolism, renal impairment, and respiratory compromise. Women should be counselled about warning signs and advised to contact their fertility clinic immediately if symptoms develop. Preventive strategies include careful gonadotrophin dosing, use of GnRH antagonist cycles, GnRH agonist trigger instead of hCG, cabergoline, cycle monitoring, and 'freeze-all' strategies to avoid fresh embryo transfer in high-risk cases.

Women with higher BMI may face increased anaesthetic and sedation risks during egg collection procedures. Treatment should be provided in appropriately equipped centres with experienced anaesthetic support.

Pregnancy complications are significantly more common in women with obesity, including gestational diabetes, pre-eclampsia, venous thromboembolism, and caesarean delivery. Women should receive preconception counselling about these risks and the importance of optimising health before conception.

Preconception and pregnancy supplementation:

• Folic acid at a higher dose of 5 mg daily is recommended for women with BMI ≥30 kg/m² to reduce neural tube defect risk, starting before conception and continuing until 12 weeks of pregnancy.

• Vitamin D 10 micrograms (400 IU) daily is advised for all women planning pregnancy and throughout pregnancy.

• Aspirin 75–150 mg once daily from 12 weeks of pregnancy until birth should be offered to women at high risk of pre-eclampsia or with more than one moderate risk factor (such as BMI ≥35 kg/m²), in line with NICE guidance.

Once pregnant, women with obesity should be referred for consultant-led antenatal care and offered additional monitoring, including oral glucose tolerance testing for gestational diabetes (usually at 24–28 weeks) and serial growth scans. Thromboprophylaxis with low-molecular-weight heparin may be required during pregnancy and the postnatal period based on individual risk assessment using RCOG guidance.

When to seek medical advice:

• Severe abdominal pain or bloating during fertility treatment

• Sudden weight gain or reduced urination

• Breathlessness or chest pain

• Positive pregnancy test – contact your GP or midwifery services promptly for early antenatal care

Women should maintain regular contact with their healthcare team throughout treatment, attending all scheduled monitoring appointments and reporting any concerning symptoms promptly to ensure optimal safety and treatment outcomes.

Reporting side effects: If you experience side effects from any medicine or medical device used during fertility treatment, you can report them via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

Frequently Asked Questions