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Obesity and miscarriage

Obesity is defined as having an excessive amount of body fat. Body mass index (BMI), a formula based on height and weight is often used to determine whether a person is obese or not. The BMI of a normal person ranges from 18.5 to 24.9. An obese person is further categorised as follows:

BMI Classification

25-29.9 Overweight

30 or more Obese

40 or more Extreme obesity

Miscarriage occurs in about 15 to 20 percent of pregnancy. Majority happen in the first in the first trimester. About 70 to 80 percent are the result of faulty genes.

Many studies have shown that obesity (BMI of 25 or more) is associated with an increased risk of miscarriage. The rate of miscarriage varies from 29 to 67 per cent according to a recent study in U.K. The higher the BMI, the greater the risk. It is interesting to note that most of the foetuses that are lost by obese mothers are genetically normal.

The exact mechanisms for the increased miscarriage rates among obese women are currently unknown. Hormonal disorders such as polycystic ovarian syndrome(PCOS), underactive thyroid (hypothyroidism) and insulin resistance are probably the contributing factors.

Women with PCOS are more likely to be overweight. By losing weight and with medical treatment, the rate of miscarriage appears to be reduced. Thyroid disorders with low levels of thyroid hormones are also linked to obesity and miscarriage.

Insulin resistance has been shown to directly affect the lining of the womb, resulting in the failure of the foetus to implant. As the risk of miscarriage with elevated BMI is high, it is important to counsel obese women on the importance of weight reduction by lifestyle modification before they embark on the journey of parenthood.

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