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Obesity in Pregnancy


The prevalence of obesity has been rising for several decades. In one study from the United States in 2003, the number of pregnant women exceeding healthy body weight was 40%.  Obesity during pregnancy is not without consequences and is linked to many maternal, fetal and neonatal complications.  Also, higher the maternal weight, the more likely complications will occur.

Definition of Obesity

The most common way to classify obesity is by body mass index (BMI) with the following levels: Underweight < 18.5, Normal 18.5 – 24.9, Overweight 25 – 29.9, Obese > 30.  Although BMI is strongly correlated with body fat content, it does have limitations and is not a diagnostic test. Some lean, muscular women may have a high BMI.  An online BMI calculator is available at

Effect of Obesity on Fertility and Early Pregnancy

Obesity has a negative impact on the ability to get pregnant and maintain an early pregnancy. Obesity increases the likelihood of irregular menstrual cycles and anovulation (not ovulating).  Obesity tends to create a sex hormone imbalance that is not favorable for reproduction. The success rates of infertility treatments are also negatively impacted in overweight women.  Obesity has also been identified as an independent risk factor for miscarriage with the risk of miscarriage increasing as the BMI increases.

Effect of Obesity on Maternal Health

Obesity increases the risk of impaired carbohydrate intolerance or diabetes. In overweight women, the incidence of gestational diabetes is 6.5 times higher than in normal weight women and the incidence in obese women is increased up to 20 fold higher.

Hypertensive disorders of pregnancy are more common among pregnant women that are obese. The incidence of gestational hypertension (increased blood pressure with no other symptoms) is increased 2 to 8 times higher. The incidence of preeclampsia (increased blood pressure along with other problems such as protein in the urine) is increased 4 to 10 times higher.

Other maternal complications before delivery that are increased in obese women include thromboembolism (blood clots), urinary tract infections, and multifetal pregnancies (twins or greater).

Obesity can also adversely affect labor and delivery. Obesity has been associated with an increased incidence of need for labor induction. Other problems that are increased include difficulty in fetal and uterine monitoring, lower success rates of  vaginal birth after c-section (VBAC), increased C-section rates, increased difficulty in performing emergency C-section, increased risk for  postpartum hemorrhage, and longer hospital stays. Obese patients also have a higher risk of complications during C-section including longer operative times, blood loss, infections, wound complications, anesthesia complications and deep vein thrombosis (blood clots).

Obese women also have a high incidence of poor lactation and difficulties in breast feeding.

Effect of Obesity on Fetal and Neonatal Health

Maternal obesity is associated with increased risks to the baby during the pregnancy, during delivery and after birth. The risk of stillbirth, particularly late and unexplained, increases as maternal weight increases. The risk is up to 3.4 fold higher in obese women compared to women of normal weight.

There is increasing evidence to support an association between maternal obesity and birth defects with the risk being increased 2-3 fold. Evidence is strongest for neural tube defects (spine and brain), heart malformations, abdominal wall defects and facial clefts. Obesity also makes it more difficult to detect birth defects with ultrasound.

Obesity does not appear to increase the risk of preterm birth from preterm labor or premature rupture of membranes (bag of water breaking) but what is more common is preterm birth due to maternal and fetal complications.

Pre-pregnancy obesity and excessive weight gain during the pregnancy are major risk factors for large for gestational infants. This increases the risk of shoulder dystocia (difficult delivery were the shoulders get stuck), birth trauma, need for C-section, fetal distress, need for resuscitation after birth, and admission to the neonatal intensive care unit.

High birth weight infants born to obese mothers are also at increased risk for childhood obesity as well as early onset of medical problems such as diabetes and hypertension.


Women need to be educated about the significant maternal and fetal risks of obesity and be advised on the extreme importance of weight loss BEFORE becoming pregnant. This will not only PREVENT complications but will also increase the chance of getting pregnant.

Obese women that are pregnant need to be aware of the increased risk of maternal and fetal complications as well as the management plans for the pregnancy to optimize the chance of a favorable outcome. However, no treatment plan during the pregnancy will improve outcome more than addressing the weight problem before getting pregnant.