Obesity can affect both partners' fertility. We treat adults with attention to health, age and the time available before a planned pregnancy. This does not replace assessment of the causes of infertility in either partner.
Can weight loss improve ovulation in PCOS?
Losing 5-15% of body weight may help improve cycles and ovulation in PCOS, but does not guarantee pregnancy. In Clark's 1998 study, of 67 women who completed a diet and exercise programme, 60 resumed ovulation, 52 became pregnant and 45 had a live birth. Only 18 pregnancies were spontaneous; the others involved fertility treatment. This was not a randomised study demonstrating that weight loss alone produces these outcomes for every woman.
In a small 2023 study, 27 women with PCOS received semaglutide 0.5 mg weekly. Average weight loss after three months was 7.6 kg. The 21 women who lost more than 5% continued for another three months: at six months, average loss was 11.5 kg, BMI changed from 34.4 to 29.4, and cycles became regular in 80% of this group. There was no control group; regular cycles do not establish a pregnancy rate. The study dose is not a plan for self-treatment.
In a trial of 72 women, liraglutide 1.8 mg daily for 26 weeks produced a weight difference of around 5.2 kg versus placebo. This differs from Saxenda 3 mg dosing and does not establish effectiveness as infertility treatment.
How does obesity affect IVF outcomes, and when should treatment not be delayed?
A 2019 meta-analysis of 21 studies found an approximately 15% lower relative live-birth rate after IVF at BMI at least 30 compared with BMI 18.5-24.9. This is not a 15 percentage-point difference or proof that losing weight before treatment improves outcomes by that amount. Planning with the fertility clinic takes account of age, ovarian reserve, diagnosis and pregnancy safety.
Fertility assessment usually starts after a year of trying for women under 35, after six months from age 35, and sooner above 40 or when a problem is already known. We do not recommend a six-month delay for everyone. Coordinated care does not mean immediately starting medication during ovarian stimulation: treatment must be agreed with the clinic beforehand, including because of anaesthesia for egg retrieval.
Poland's government programme covers women up to age 42 using their own eggs or donor sperm, up to 45 using donor eggs or embryos, and men up to 55. It provides six individualised procedures in different combinations, including up to four cycles with the couple's own reproductive cells or donor sperm. A year of trying does not automatically establish eligibility: the centre checks, among other conditions, a documented absolute cause of infertility or unsuccessful treatment in line with standards during the preceding 12 months.
Low testosterone with obesity: assessment and treatment for men planning fatherhood
A meta-analysis of 21 studies involving 13,077 men found abnormal sperm counts more often with obesity. In another review of 24 studies, testosterone rose by an average of 2.9 nmol/L after dietary treatment and 8.7 nmol/L after bariatric surgery. These are group averages, not individual predictions. A review of 32 studies in a 2026 journal volume highlights the limited quality of evidence on improvements in semen; hormone changes do not establish the likelihood of pregnancy.
Testosterone supplied from outside the body can suppress sperm production, so men planning fatherhood should not use it on their own. A low result needs confirmation and investigation of its cause. Obesity treatment can proceed alongside appropriate andrology or endocrinology assessment.
When should medication be stopped before pregnancy, and can it affect contraception?
If pregnancy is possible, effective contraception is agreed before treatment. The last dose is timed relative to planned conception, not only embryo transfer: natural conception may also occur.
| Medicine | Contraception during treatment | Stopping before planned pregnancy | Pregnancy and breastfeeding |
|---|
Semaglutide | Effective contraception if pregnancy is possible; follow advice for vomiting or diarrhoea | At least 2 months before planned conception | Do not use during pregnancy or breastfeeding |
Tirzepatide | Effective contraception; additional protection for 4 weeks after starting and dose increases is a clinic precaution, not a manufacturer's requirement | At least one month before planned conception | Not recommended during pregnancy; product information allows individual consideration during breastfeeding |
Liraglutide | Effective contraception if pregnancy is possible | Stop when pregnancy is planned or recognised | Do not use during pregnancy or breastfeeding |
Naltrexone/bupropion | Effective contraception if pregnancy is possible | Do not use while trying to conceive | Do not use during pregnancy or breastfeeding |
Orlistat | Effective contraception; additional protection with the pill during severe diarrhoea | Our programme stops it before attempts to conceive | Product information advises caution in pregnancy; our clinic does not use it for weight loss in pregnancy. Breastfeeding is a contraindication |
European Mounjaro product information does not require adjustment of oral contraceptive doses. However, our clinic recommends an additional barrier method for four weeks after starting tirzepatide and after each dose increase, or considering a non-oral method. This is a precaution consistent with US information, not a requirement in the EU product information. Vomiting and severe diarrhoea can affect the pill's effectiveness with other medicines too; follow its leaflet.
An intrauterine device or implant may be suitable, but the method should be chosen individually with a gynaecologist. Seek help promptly if emergency contraception is needed. Evidence on the effect of higher body weight on its efficacy is inconsistent; 70 kg is not an established cut-off and should not delay advice.
What happens if a patient becomes pregnant during treatment, and how is pregnancy managed with obesity?
After a positive pregnancy test, stop semaglutide or tirzepatide and contact your doctor and gynaecologist promptly. Give the medicine's name, dose and date last taken. If you use another preparation, also seek prompt advice; our programme does not use medication to promote weight loss during pregnancy.
In a 2026 observational analysis of 429 women exposed to semaglutide in early pregnancy, some complications were more frequent than among nonusers, but no significant differences were found compared with women who stopped before pregnancy. The authors considered effects of discontinuation as a possible explanation. The study does not prove that appetite rebound alone caused the findings or that the medicine has no effect on the fetus. Evidence remains limited and requires individual assessment.
For a singleton pregnancy with prepregnancy BMI at least 30, the usual recommended total weight gain is 5-9 kg; this is not advice to lose weight. Nutritional support helps limit excessive gain after stopping medication. PTLO 2024 recommends 800 micrograms of folate daily before pregnancy for women with obesity; agree the dose and preparation with your doctor, especially after bariatric surgery. With obesity, the doctor arranges early glucose assessment, including an OGTT for those at risk. A normal early result does not replace repeat testing at 24-28 weeks. Some bariatric operations require another way of monitoring glucose.