Several factors, many of which are self-manageable, can be the source of complications in women during conception and pregnancy. One such factor, which is also very common, is improper Body Mass Index. Body Mass Index (or BMI) is a composite value 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 display 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 probablity of health problems for the baby. An obese mom-to-be is at a higher risk of hypertension, blood clotting disorders, gestational diabetes and, in the worst case, miscarriage. These women, may have a higher chance of need for induction of labour and/or a caesarean birth.

Low BMI and Fertility

Similar to high BMI, low BMI can also cause 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 can 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 depending on the deviation from the normal range. 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 best way to naturally lose weight. However the reduction should be gradual as a drastic cut can trigger a slowing down of the body metabolism. Fresh, whole foods should be consumed for getting maximum nutritional value and consumption of foods with 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 aim to increase the amount of daily physical activity if one’s lifestyle is generally sedentary.

Most people believe that it is easier to increase a low BMI than to decrease it when it is higher. This is however not exactly true. A controlled diet with the necessary amount of nutritional content is essential for even increasing BMI, while remaining healthy. Consultation with a dietician may be advisable to get an individually customized diet for those aiming to correct their BMI. Nutritional foods, multiple small meals instead of one large meal, drinking sufficient water between meals and continuation of moderate exercise can help increase BMI while keeping the body healthy. 

Sometimes medical problems may be the cause of a low  BMI, even with a good 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 negative impact of a low or high BMI on fertility is valid also for men. 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. Besides controlling their calorie intake, following a healthy lifestyle with sufficient amount of regular physical exercise, can help men achieve normal BMI.

Ensuring that your BMI is normal is important, not just when one is trying to conceive, but always throughout life.