Starting with getting pregnant, obesity (a BMI over 30) is often related to increased adipose (fat) tissue, and this adipose tissue actually makes its own hormones that can disrupt ovulation. If no egg is released, then pregnancy can’t happen. Even with successful ovulation and pregnancy, the risk of miscarriage increases by 3%, and there is also an increased chance of birth defects such as neural tube defects (problems with the spine) as well as heart defects. This can be associated with either a problem with chromosomes (genetic material) in the egg or during the development and growth of the pregnancy.
Unfortunately, there are also increased chances of maternal health issues during pregnancy with higher BMI. For preeclampsia (blood pressure issues in pregnancy that may cause seizure/stroke, kidney/liver damage, or even death), the single greatest risk factor is obesity, which is present in about 1/3 of cases. In fact, women with a BMI >30 are 3 times more likely to develop preeclampsia than those women who begin pregnancy with a BMI in the normal range. Why do we care? Blood pressure issues in pregnancy are the most common cause of maternal death in most developed countries, like the U.S.
Blood sugar issues are another problem that is more common in obese women during pregnancy. Gestational (pregnancy-related) diabetes risk increases as maternal BMI increases. While only about 2.5% of women with a normal BMI develop gestational diabetes, this increases to about 5% with a pre-pregnancy BMI of 30 and to more than 10% for a BMI >35. While it’s certainly not enjoyable to watch one’s diet before pregnancy, having to prick a finger to check blood sugar and taking or injecting medicine during pregnancy would definitely be less fun.
Even delivering the baby can be tougher for obese moms. Labor tends to last longer, the chances of needing a cesarean section are higher, and babies tend to be bigger. For moms with a starting BMI >30, the chances of delivering an 8 lb 13 oz baby is as high as 15%, and the chances of having a baby weigh nearly 10 lbs or more is about 4%. In comparison, mothers with a normal BMI have less than a 10% chance and about a 1% chance, respectively. The issues with larger babies are that they often have to stay in the hospital longer as they can have trouble with their blood sugar or they can potentially get hurt if they get stuck during the delivery. In fact, baby size alone increases the odds of needing a cesarean section to deliver the baby.
Of course, not all obese mothers have poor pregnancy outcomes, and not all normal weight mothers have good pregnancy outcomes. Also, we’d definitely not advise intentional weight loss during pregnancy. Still, working to attain a healthy weight prior to conceiving and monitoring weight gain during pregnancy do decrease the risk of pregnancy complications, and that happy, health pregnancy is what it’s all about 😊