From a medical point of view, obesity is not an aesthetic issue but a chronic systemic disease that directly affects reproductive system functions. The main problem when trying to conceive is excessive adipose tissue which no longer plays only a role of an energy storage but also becomes a highly active endocrine organ.
Substances and hormones produced by adipose tissue influence the hypothalamic-pituitary-ovarian axis, leading to significant hormonal disturbances. As a result, women often experience irregular menstrual cycles, less frequent ovulation, or the complete absence of ovulation (anovulatory cycles), as well as reduced egg quality.
At our Polish medical and dental practice, we diagnose and treat causes of infertility on a daily basis. We offer specialist medical consultations in London for our patients. Clinical practice shows that difficulties conceiving often have a metabolic background. For this reason, our clinic also includes a diet clinic.
In this article, we answer the question: why does obesity cause problems with getting pregnant?
Impact of a high BMI on female fertility and the reproductive system
Excess body weight is a medical risk factor for infertility. Obesity in women is diagnosed when the body mass index (BMI) is 30 or higher. This condition directly influences physiology of the reproductive system and makes it more difficult to conceive.
Adipose tissue works as an active endocrine organ, releasing hormones. Increased amount of body fat leads to excessive production of oestrogens and signalling proteins (adipokines). An excess of these substances disrupts hormonal balance, including the hypothalamic-pituitary-ovarian axis function, which regulates the menstrual cycle.
As a result, patients diagnosed with obesity often experience menstrual disorders, including infrequent ovulation (oligo-ovulation) and complete absence of ovulation (anovulation). Without the release of an egg, fertilisation cannot occur.
In addition, a high BMI negatively affects metabolic parameters and increases the risk of insulin resistance.
Treatment of infertility in this group of patients requires both medical and dietary management. The first step in therapy is weight reduction under supervision of a doctor and clinical dietitian. Reducing body fat helps stabilise hormone levels and supports the restoration of regular ovulatory cycles.
Impact of metabolic disorders on hormonal balance
Obesity, particularly abdominal (visceral) obesity, is a major risk factor for the development of insulin resistance. This is a pathological condition in which peripheral tissues (muscle, adipose tissue, and liver) show reduced sensitivity to insulin, the hormone responsible for regulating blood glucose levels.
Response to insulin resistance is activation of a compensatory mechanism. Pancreas increases insulin secretion, which leads to hyperinsulinemia, a chronically elevated level of insulin in the blood. This condition directly affects the female reproductive system function.
Hyperinsulinemia and excess androgens (hyperandrogenism)
High insulin levels affect the ovaries through specific receptors. Hyperinsulinemia stimulates theca cells in the ovaries to produce excessive amounts of androgens, including testosterone.
Additionally, elevated insulin levels inhibit the synthesis of SHBG (sex hormone-binding globulin) in the liver. This protein binds testosterone in the bloodstream. Reduced SHBG levels increase the amount of free, biologically active testosterone in circulation. Excess male sex hormones in women (hyperandrogenism) is one of the key factors disrupting the normal menstrual cycle.
Link between obesity, PCOS, and lack of ovulation
Coexistence of insulin resistance, hyperinsulinemia, and hyperandrogenism directly disrupts the process of folliculogenesis (growth and maturation of ovarian follicles). High androgen levels stop follicle development at an early stage.
As a result, a dominant follicle does not develop, and a mature egg is not released. This phenomenon is known as anovulation. Immature follicles accumulate in the ovaries as small cysts. This clinical picture is characteristic of polycystic ovary syndrome (PCOS), one of the most common endocrine causes of female infertility.
Obesity is diagnosed in 40–80% of patients with PCOS. High BMI significantly worsens the symptoms of this condition, intensifying metabolic and hormonal disturbances and further reducing the likelihood of natural conception.
Obesity and egg quality
Significant excess of fat tissue induces a chronic low-grade inflammatory process in the body. Adipocytes (fat cells) in patients with a high BMI release increased amount of pro-inflammatory cytokines, including interleukin-6 (IL-6) and tumour necrosis factor alpha (TNF-α).
Presence of inflammatory markers in the ovarian follicular fluid negatively affects the quality of oocytes (egg cells). Elevated cytokine levels alter the microenvironment of the developing follicle. At the same time, obese patients often experience oxidative stress, characterised by increased levels of reactive oxygen species (ROS).
High levels of free oxygen radicals can cause structural damage to oocytes, including DNA degradation, mitochondrial dysfunction, and abnormalities in the spindle apparatus. Reduced egg quality directly lowers fertilisation rates and increases the risk of genetic abnormalities (aneuploidy) during embryo development.
Impact of high BMI on embryo implantation
Successful fertilisation is only the first step in reproduction. The next stage required for pregnancy is implantation of the embryo in the uterine lining (endometrium). Obesity has been shown to reduce endometrial receptivity, which is the ability of the uterine lining to accept and sustain an embryo.
Metabolic disturbances, hyperinsulinemia, and imbalances in steroid hormones (oestrogen and progesterone) alter gene expression in endometrial tissue. This disrupts decidualisation, the morphological and biochemical transformation of the uterine lining during the luteal phase of the menstrual cycle.
Clinical studies confirm that patients diagnosed with obesity have a statistically lower rate of successful implantation compared with women with a normal BMI. This relationship occurs both in natural conception and during assisted reproductive treatments, such as in vitro fertilisation (IVF). Reduced endometrial receptivity in obese patients is also associated with a higher risk of early pregnancy loss (miscarriage).
Impact of excess body weight on male fertility
When couples experience difficulty conceiving, diagnosis often initially focuses on the woman's health. However, fertility is always a matter involving two people. Male fertility factors account for around half of cases of conception difficulties. Excess body weight in men is one of the factors that can reduce chances of pregnancy, but what’s important, it is a treatable condition.
How does a high BMI affect the male body when trying to conceive? Three main mechanisms are involved:
Fat tissue in men is hormonally active and produces enzymes that convert testosterone into oestrogens. This reduces testosterone levels in the blood, when testosterone is essential for correct sperm production.
Men diagnosed with obesity often have poorer semen parameters, typically lower sperm count, reduced motility, and abnormal morphology. Obesity also increases inflammation in the body, which may damage sperm DNA.
For healthy sperm production, testes need to remain 1–2°C cooler than the rest of the body. Excess fat tissue around the thighs and lower abdomen makes heat dissipation more difficult. As a result, the testes may overheat, which directly inhibits sperm production.
Obesity and planned pregnancy – summary
Trying to lose weight can be extremely frustrating, especially when the scale does not change despite your significant effort. From a medical point of view, it’s rarely caused by lack of willpower. More often, the issue lies in undiagnosed metabolic barriers, such as insulin resistance or thyroid disorders, which are difficult to overcome without appropriate treatment.
If you are struggling to lose weight and feel that you are wasting time on ineffective diets, consider seeking help from our doctors and diet clinic.
If you are planning a pregnancy and are concerned that excess weight may make it harder to conceive or affect your baby’s health, it is worth trying to lose weight under specialist control.
We understand these concerns and know how difficult it can be to seek help within a foreign healthcare system. That is why our Polish gynaecologist in the UK provides professional support in your native language.
Instead of trying restrictive diets, book a consultation. Together we will identify the medical cause of your difficulties and help prepare your body for a safe and healthy pregnancy
