Effect of BMI on Fertility

Reviewed on : 17 June 2016

There are several common factors, that can become the source of complications during conception and pregnancy. Fortunately, many of these factors are manageable to avoid the complications in the first place. Among these factors, the most common one is improper Body Mass Index or BMI, which is a composite figure calculated using one’s height and weight. As per WHO classification, BMI below 18.5 is categorized as underweight, between 18.5 and 24.9 as normal, between 25 and 29.9 as overweight and between 30 and 34.9 as Class 1 obesity. Anything other than the normal range is not good for either conception or pregnancy.

High BMI and Fertility

High BMI has been associated with ovulatory subfertility and anovulatory infertility. Women with high BMI can also have a hormonal imbalance which either causes irregular ovulation or prevents them completely from ovulating.  Unfortunately, women who are obese or overweight also do not respond as well when it comes to fertility treatment.

An adverse effect of high BMI is production of fewer follicles. These follicles are almost spheroid cellular aggregations which secrete hormones that then affect various stages of a woman’s menstrual cycle. This decrease in follicles also lowers the amount of oocytes, which are female gametocyte or germ cells involved in reproduction.

Obesity is also associated with polycystic ovary syndrome (PCOS). Being obese also increases the chances of health problems for the baby. An obese mom-to-be is at higher risk of hypertension, blood clotting disorders, gestational diabetes and in the worst case, miscarriage. For these women, there may be a higher need for induction of labour and the chances of a caesarean birth also increase.

Low BMI and Fertility

Similar to high BMI, low BMI can also lead to problems with fertility, as it can cause a hormonal imbalance which results in  problems in conceiving. Since estrogen is partially produced from body fat, low fat content in the body also means lower estrogen levels.

Low body fat also disrupts the flow of hormones from the pituitary gland, which signal the ovaries to release an egg. Absence of this signal will cause the egg to remain in the ovaries and not descend. So a certain minimum amount of body fat is required to ovulate even if a woman experiences regular periods.

Targeting a normal BMI

Achieving a normal BMI is not very hard and also depends on how much it deviates from the normal range to begin with. Regardless, a healthy diet clubbed with regular exercise can go a long way in normalizing the BMI.

Health experts have suggested that reducing the calorie intake is the fastest way to naturally lose weight. However the reduction should be monitored as a drastic cut  can also prevent weight loss by triggering a slowing down of the metabolism in the body. Fresh, whole foods should be consumed for the maximum nutritional value and consumption of foods with a high sugar content should be strictly avoided.

Regular exercises can also help in lowering one’s BMI. According to the Center for Disease Control, 150 minutes of aerobic exercise per week, including muscle strengthening activity on 2 or more days per week, can be very helpful. In general, one should increase the amount of daily physical activity if one’s lifestyle is generally sedentary.

If the BMI is low to begin  with then one has to work towards increasing it, which, many believe, is easier than decreasing it. All one has to do is eat more….well, not exactly. A controlled diet with the necessary amount of nutritional content is essential for increasing BMI while remaining healthy. Consultation with a dietician may be advisable to get an individually customized diet.

To increase one’s BMI, a calorie-rich but balanced diet should be consumed. Foods like yogurt can supply healthy nutrition as well as the necessary calories that the body requires. Those trying to increase their BMI should also avoid large meals and instead eat smaller portions more frequently. According to Mayo Clinic, at least five meals per day should be consumed. One should drink water in between meals. If one exercises vigorously, one should not stop it all together in an effort to increase their BMI. A minimal amount of exercise daily will increase one’s appetite and also keep the body healthy.

Some people might be suffering from certain health problems that might be the cause of a low  BMI, even after a sufficient diet. In such cases, it is recommended to contact a healthcare provider to diagnose and treat the underlying health issue before starting a regime to increase the BMI.

The impact of a low or  high BMI on fertility holds true for men too. Being overweight or obese increases the chances of having poorer sperm quality. It also increases the chances of having a low sperm count. The hormonal changes associated with low or high BMI can reduce a man’s sexual drive. Men who are overweight might also experience  problems in getting an erection. Men can also reduce or increase their calorie intake to lower or increase their BMI, besides following a healthy lifestyle with sufficient amount of regular physical exercise.  

A high BMI can also lead to high cholesterol and/or poor heart function in both men and women.

Just as women need to watch their BMI, especially when they are trying to conceive, men also need to be careful that their BMI is in the normal range. Ensuring that your BMI is normal is important, not just when one is trying to conceive, but always throughout life.

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