Over the last decades, the proportion of people who are overweight or obese is increasing rapidly worldwide. In Hungary, 30 percent of the adult population is considered obese and another 30 percent is overweight (1). According to an evaluation of Semmelweis and Debrecen university in 2015, the prevalence of overweight and obesity women 35–59 years occurred in 36.8% and 38.7%, respectively (2). Surprisingly, at their reproductive lifetime, these ratios are alarming high. Although we know that excess weight is linked to many health consequences, little is known about its negative effect on fertility.
Effects on hormon balance
A fine hormonal balance regulates the menstrual cycle. Overweight and obese women have higher levels of a hormone called leptin, which is produced in fatty tissue. This excess hormon can disrupt the hormone balance and lead to fertility difficulties.
Excess weight is often associated with insulin resistance and hyperinsulinemia. This will stimulate increased production of androgen, and androgen will have feedback on gonadotropin production. This presents with menstruation abnormalities and ovulatory dysfunction. One study found that women who were obese were much less likely to conceive within one year of stopping contraception than women in the normal weight range (66.4% compared with 81.4%, respectively).
Effects on oocytes (women’ eggs)
Among obesity women, changes in the hormonal balance also increase the risk of anovulation, which means an ovulation without egg. Women with a body mass index (BMI) above 27 are 3 times more unable to conceive than women in the normal weight range. Just because they don’t ovulate.
For those who undergoing IVF, they often need higher gonadotropins doses and longer treatment course for follicular development. However, it was showed that oocytes are smaller and less likely to mature.
Effects on embryos
In human IVF cycles, obese women have greater chance of making poor quality embryos. This is often caused by high level of leptin, which effect the stem cells growth and proliferation. Obviously, a poor quality embryo has less chance to survive and develop, compared to fine embryo. It was demonstrated that each unit of BMI above 29 reduces the chance of getting pregnancy within a year by 4%. This means that for a woman with a BMI =35, the likelihood of getting pregnant within a year is 26% lower, and for a woman with a BMI = 40 it is 43%, lower compared with women with a BMI = 29.
Effects on live birth rate
And when couples use IVF to conceive, the chance of a live birth is lower for women who are overweight or obese than for women with normal BMI. On average, compared to women in the healthy weight range, the chance of a live birth with IVF is reduced by 9% in women who are overweight and 20% in obese women.
Effects on children
Increasing evidence suggests that metabolic obesity can transfer through generations. Children of obese mothers have more chance of developing obesity, type 2 diabetes and cardiovascular diseases (3).
While obesity seems upset us a lot, there is good news too. Weight-loss can promote menstrual cycle regularity and improve the chance of pregnancy. In obese women with anovulatory infertility, even a modest weight loss of 10% can improve about 30% chance of conceiving (3). Weight loss is also help women need less IVF treatment cycles, reduce risks during pregancy, and increase live birth rate.
For those obese, a weight loss of at least 10% body weight should be a goal to improve their health and fertility capacity. Excercise regularly at least 30 minutes per day, maintain healthy diet, and having medical interventions if necessary can help people to get rid of excessive weight. Lastly, men and women are twice as likely to make positive health behaviour change if their partner does too. So becoming pregnant will be more likely if couples exercise and diet together.
- Elhízó Magyarország. A túlsúly és az elhízás trendjeés prevalenciája Magyarországon 2015. 2016, DOI: 10.1556/650.2016.30389
- An update of impact of obesity on female infertility and its management, Int J Pregn& Childbirth, 2018, 4(2): 84-90