The Ideal Body Weight for Pregnancy

An extreme in weight either too thin or too heavy is the most serious lifestyle factor adversely affecting reproductive health. Weight is defined by Body Mass Index (BMI) which comprises weight and height. The ideal body weight for pregnancy is a BMI between 19 and 28 which for 5 foot 5 inch women would be a weight between 114 and 168 pounds.

Underweight and Fertility

Underweight is defined as a BMI less than 19 which is equivalent to a 5 feet 5 inch woman weighing less than 114 pounds. Infertility is more likely to occur in underweight than normal weight women due to ovulation dysfunction. The incidence of early miscarriage is also increased in underweight women most likely due to hormone imbalance.

Obesity and Fertility

Obesity defined as a BMI over 30 is a prevalent medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health. A BMI of 30-35 which for a 5 foot 5 inch woman would be a body weight of between 180 and 210 pounds may reduce life expectancy by two to four years while severe obesity defined as a BMI greater than 40 which for a 5 foot 5 inch woman would be a body weight over 210 pounds reduces life expectancy for men by as much as 20 years and five years for women. Obesity is thus the leading preventable cause of death and is the most serious public health problem in the 21st Century.

Obesity is most commonly due to a combination of excessive dietary calories, lack of physical activity and genetic susceptibility, though a limited number of cases are due solely to genetics, medical reasons or psychiatric illness.

Obesity is associated with many diseases particularly heart disease, stroke, type 2 diabetes, breathing difficulties during sleep (apnea), certain types of cancers (breast and uterine), osteoarthritis, infertility and miscarriage. An elevated BMI may be associated with ovulation dysfunction, polycystic ovarian syndrome (PCOS), higher use and dosages of ovulation induction medications, poor egg and embryo quality, implantation failure and early pregnancy loss most likely due to hormone imbalance involving both excessive estrogen and androgen (male hormone) production. Men with obesity also have a higher chance of sperm abnormalities including low testosterone production, low sperm counts, low motility and poor sperm morphology.

The Impact of Obesity on Egg Quality

Poor fertilization and embryo quality and a higher chance of implantation failure and early pregnancy loss are also associated with both male and female obesity. IVF success rates have been reported to be as much as 33% less for obese women and many programs do not offer IVF services to women with a BMI over 40 due to the very low probability of a successful pregnancy. In our IVF program appropriately high successful pregnancy rates occur in women whose BMI is greater than 20 but less than 35. Obese women who do become pregnant are more susceptible to gestational diabetes, pregnancy induced hypertension; pre-eclampsia, operative delivery, birth trauma, anesthesia-related problems and poor wound healing.

It’s not always easy to lose weight. However, relatively small amounts of weight loss (average 12 to 15 pounds or greater than 5% of body weight) may be sufficient in ameliorating reproductive function in many having reproductive difficulty.

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If you are having difficulty getting pregnant and would like to learn more about the ideal body weight for pregnancy, please contact us for a consultation!