Before talking about ovulation, ovarian reserve or couple fertility, there is a pillar that usually comes first when a woman wants to become a mother: lifestyle. Although there are multiple factors that can influence the possibility of conceiving, weight often quickly becomes the center of the conversation when there is overweight or obesity, often summarized in a categorical guideline: “first you have to lose weight.”
The premise seems logical and simple on paper. However, in practice, it is often overlooked that obesity is not just a matter of extra kilos nor a direct consequence of lack of willpower. It is a complex chronic disease capable of modifying different processes in the body, some of them related to reproduction.
This dilemma between the desire for motherhood and clinical warnings reminds me of the experience of Australian actress Rebel Wilson. In her memoir Rebel Rising (2024), the star of Pitch Perfect recounted that her decision to start the so-called “year of health” in 2020 stemmed from a very clear medical indication: a fertility specialist warned her about her difficulties conceiving due to polycystic ovary metabolic syndrome (PCOS), so she would have much higher chances of successfully freezing eggs if she managed to lose weight, a process that led her to lose more than 30 kilos.
Stories like these make me wonder as a woman what really happens in the body when obesity exists, and to what extent it really influences the path to better fertility? Understanding it requires looking beyond the number on the scale.
Obesity and fertility: the relationship is real, but not so simple
Talking about obesity and fertility should not automatically lead to the conclusion that a woman with excess weight will have difficulties getting pregnant. “The relationship is important, but it is not absolute, so living with obesity does not necessarily mean a woman will not succeed. In fact, many conceive spontaneously,” explained Dr. Patrick Jacinto, from the Scientific University of the South, to Somos.
What can change is the reproductive scenario. One reason is that adipose tissue is not metabolically passive. As Dolores Mejía, an expert in endocrinology and nutrition and president of the Dominican Diabetes Observatory, explained, the greater the amount of fat, the higher the aromatization activity, a process by which estrogens are produced from androgens. This hormonal excess can alter the functioning of the hypothalamic-pituitary-ovarian axis, which regulates reproductive function.
Added to this are insulin resistance and the proinflammatory state associated with obesity, which can create a metabolic environment capable of interfering with ovulation. “This context can also increase the risk of metabolic complications during pregnancy, such as gestational diabetes. In fact, 10% of women who develop it may remain diabetic forever, eventually developing type 2 diabetes,” warned Mejía.
And here appears one of the most important nuances: having regular menstruations does not necessarily mean that all processes related to fertility are functioning optimally. As obstetric gynecologist Rebecca Starck from Cleveland Clinic pointed out, a woman with obesity may continue menstruating every month and still have alterations in ovulation, egg quality, or endometrial receptivity. A regular period is a favorable sign but does not rule out other factors involved in fertility.
This mechanism becomes even tighter when conditions such as polycystic ovary metabolic syndrome (PCOS) or endometriosis are added. In the case of PCOS, insulin and androgen levels directly interfere with the maturation and release of eggs—an obstacle that Rebel Wilson herself had to face during her IVF treatments. On the other hand, obesity is characterized by a low-grade systemic inflammatory state that can add to the estrogen-dependent inflammatory component of endometriosis, creating mechanisms that affect reproductive function.
Should you lose weight before trying to get pregnant?
It is very common for a woman with overweight or obesity who wants to get pregnant to hear the famous phrase: “first you have to lose weight.” But when does this indication have a real medical basis and when does it become a dangerous simplification?
The answer cannot be separated from age and reproductive time. “That is an important decision that must be individualized, depending on the patient’s age, because we know women have a biological clock,” said Dr. Alicia Seminario, gynecologist at Ricardo Palma Clinic.
A patient around 28 years old with overweight and irregular cycles, who may have some margin to improve her metabolic state before trying to conceive, is not the same as a woman of 38 or 40 years with low ovarian reserve. In the latter case, “she may not necessarily be able to afford to wait a year trying to improve her metabolic state when her ovarian reserve is working against her,” emphasized Seminario.
That does not mean that taking care of metabolic health stops being important. On the contrary, carrying a pregnancy in the best possible conditions will always be the ideal scenario. As Dr. Mejía emphasized, the optimum is that pregnancy—a state that by itself increases weight by 11 to 13 kilos and naturally generates insulin resistance—does not come as a surprise but is planned to prevent complications such as gestational diabetes, miscarriage, macrosomia, stillbirth, among others.
However, when reaching normal weight is not always an immediate option, there are some very clear clinical goals. Achieving an initial 7% reduction in body weight already represents a very powerful metabolic turning point to improve insulin sensitivity and ovulation; however, when seeking a deeper impact on the metabolic profile, Mejía indicated that “the minimum negotiable that I personally recommend, if reaching normal weight is not possible, is that those living with obesity lose at least 15% of their weight.”
The goal, moreover, should not be reduced to seeing a number drop on the scale. Body Mass Index (BMI) is often used for practicality, but the focus is also on modifying body composition: reducing visceral fat and preserving or increasing muscle mass generates metabolic benefits, even when the scale drop is not drastic.
Treatments, IVF, and medications: what changes on the path to pregnancy?
When a woman with obesity needs to resort to a fertility treatment—such as in vitro fertilization (IVF)—the clinical picture can be very different.
According to Dr. Karina Espíritu, gynecologist at Clínica Internacional, obesity can be associated with a lower response to ovarian stimulation, the need for higher doses of medications, a lower number of eggs retrieved in some patients, and in certain cases, lower implantation or pregnancy rates.
This is exactly what Rebel Wilson experienced on her path to motherhood: her IVF process was full of setbacks in the laboratory, with multiple attempts and the loss of eggs that did not survive, until managing to obtain a single viable embryo with her own genetic material after considerable emotional exhaustion.
But the impact does not end in the laboratory. During pregnancy, obesity can also increase the risk of complications such as gestational diabetes and hypertension. However, this does not mean that a woman with obesity cannot undergo fertility treatment, but it is advisable to individually evaluate the safest timing and conditions to do so.
In that process, weight management can include different tools. The basis remains lifestyle changes. As Dolores Mejía detailed, this includes a hyperproteic and hypocaloric dietary pattern—with at least 1.5 grams of protein per kilo of weight—combined with between 150 and 300 minutes per week of physical activity, integrating both cardiovascular and strength exercises.
Added to this is working on other factors that can affect metabolic health: controlling chronic stress or distress (which raises cortisol and favors visceral fat accumulation) and strict sleep hygiene that guarantees at least seven hours of rest.
When habit changes alone are not enough and it is necessary to move towards pharmacological or surgical options, waiting times and planning take on a critical role. In the case of bariatric surgery, the ideal is to wait between 12 and 24 months before trying to get pregnant, carefully evaluating the type of procedure performed.
On the other hand, obesity medications that act on the GLP-1 receptor pathway, such as semaglutide (Ozempic), also require careful planning when pregnancy is desired. Although they are very effective for metabolic control and satiety, they should not be used during pregnancy; in fact, regulatory indications for drugs like semaglutide include a suspension period of at least two months before attempting conception.
Before trying to get pregnant, look beyond the scale
When a woman living with obesity decides to take the step towards motherhood, the starting point should not be an isolated demand about weight, but a comprehensive and respectful preconception evaluation.
According to Dr. Rebeca Starck, this process should always start with a stigma-free conversation that reviews much more than BMI: family history, medical history, menstrual cycle, ovulation, age, medications, blood pressure, diabetes, insulin resistance, thyroid health, gynecological history, pelvic pain, endometriosis, fibroids, previous surgeries, miscarriages, and also male factors.
The evaluation should also consider diet, physical activity, and emotional health. While weight is part of the medical equation, it should never become the only explanation nor a wall that overshadows the desire for motherhood.
Medical decisions should consider the safest alternatives according to each personal context. For example, faced with the limitation of having only one viable embryo and seeking to maximize the statistical chances of success without risking her health, Rebel Wilson and her medical team opted for surrogacy, allowing a surrogate mother to carry the pregnancy of her daughter Royce Lillian, born in November 2022.
Therefore, the key lies in seeking comprehensive support where the goal is not to judge the body the patient inhabits, but to guide her with empathy to make safe, realistic, informed, and above all, personalized decisions.
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