Low BMI & Pregnancy Rates

Ideally, a woman's overall health would be at an optimal level before conception. Good nutrition plays an important role during pregnancy. The body mass index, or BMI, is an important indicator of nutritional status. A BMI outside of the normal range is an indicator of increased risk for adverse pregnancy outcomes.

Body Mass Index

Body mass index, BMI, is a simple measurement calculated from a person's weight and height. The Centers for Disease Control and Prevention indicates, "BMI provides a reliable indicator of body fatness for most people and is used to screen for weight categories that may lead to health problems." The range of a normal BMI is 19.8 to 26. This range is indicative of healthy weight status and the best pregnancy outcomes.

Miscarriage

Results of research conducted by several university's in Finland found that women with very low BMI's are at increased risk of miscarriage (see Reference 2). This increased risk was inclusive of naturally conceived pregnancies and those attained through fertility treatments. It was proposed that leptin, a hormone involved in fertility and regulated in the adipose tissue or fat, is inadequate in very thin women. Without adequate fat reserves, leptin levels fall outside of the ideal range, which can decrease egg quality and increase rate of miscarriage (see Reference 3).

Preterm Birth

Research published in the Journal of Obstetrics and Gynecology stated women who were underweight before becoming pregnant and did not gain adequate weight during pregnancy to be at increased risk of preterm labor (see Reference 4). "Women with a pre-pregnancy BMI less than 19.1 had a significantly increased risk of delivering preterm," according to the Journal of Nutrition. However, some researchers in this study found that underweight women who gained adequate weight at a gradual rate during their pregnancy saw a decreased rate of early labor to a more normal range (see Reference 5).

Low Birth Weight

The University of Maryland Medical Center defines low birth weight babies as those infants weighing less that 5.5 pounds at birth (see Reference 6). "Women with a low BMI were more likely to have an infant that was smaller or of lower birth weight than infants born to women with either a normal or high BMI," according to the Journal of Nutrition (see Reference 5). A bulletin published by the World Health Organization further confirms that women who are have a low BMI are at a particularly high risk of a low birth weight baby (see Reference 7).

Recommendations

Women, particularly those whose BMI falls outside of the normal range, should consult with a physician prior to conception to ensure optimal health for gestation. Ideally, women with low BMIs would follow the advice of a doctor or registered dietitian to gain weight until her BMI is within the normal range. Once pregnant, the mother-to-be should attain prenatal care and follow the advice of her doctor to gain weight in the optimal range and ensure that her fetus is developing normally.