The information provided below is for readers based in the United States of America. Readers outside of the United States of America should seek the information from local sources.

What is obesity?

Obesity is the presence of too much body fat. Technically it is not the same thing as being overweight, because higher-than-average weight also can result not only from increased fat, but also due to issues involving body water, bone, and muscle. Clinically, obesity is defined in terms of a ratio called the body mass index (BMI), which is calculated as a persons weight in kilograms (really the mass) divided by the square of their height in meters:

A person is defined as overweight if their BMI is in the range of 25-30 kg/m2, and obese if their BMI is 30 or higher. Generally, the formula is a good measure of obesity, but theres an important caveat. Since muscle is very heavy, and more dense than fat, BMI comes out elevated in people who are especially muscular and whose fraction of body fat mass is very low compared with their total mass. Using the BMI calculation alone, somebody with a body builder physique would be misclassified as obese, despite being ripped with a washboard abdomen. Its thus very important for an examiner to look at the person to determine whether a simple BMI calculation is appropriate.

The body builder scenario notwithstanding, applied to people of average musculature, a BMI from 18.5 to 24.5 is normal (17.5 -18.4 is underweight, while BMI below 17.5 indicates anorexia), where as 25 and higher is a sign for your doctor that it is appropriate to discuss health risks and interventions, such as exercise and diets, whether you are pregnant or not. As for BMIs in the obese range, these are further categorized into three classes of severity:

  • Class 1: BMI 30.0 34.9 kg/m2 Low Risk
  • Class 2: BMI 35.0 39.0 kg/m2 Moderate Risk
  • Class 3: BMI 40 kg/m2 and up High Risk

The obesity classes and risk categories are applicable both to non-pregnant and pregnant patients. However, in the setting of pregnancy, the risk of serious complications and death amplifies as the pregnancy progresses with increasing BMI.

How common is obesity during pregnancy?

Obesity is extremely common during pregnancy. In fact, both in and out of pregnancy, obesity is the most common public health problem. Affecting more than 36 percent of adults in the United States, it is the absolute most common health risk, even more common than smoking. For women in pregnancy, the prevalence of obesity is not quite as high as in the general population, but it does complicate roughly a quarter of pregnancies. According to statistics reported by the US Centers for Disease Control and Prevention, 25.6 percent of pregnant women were overweight (BMI 25-29.9) in the year 2014, and 24.8 percent were obese (BMI >/= 30).

How is obesity diagnosed?

The diagnosis depends first on your BMI. For those with a BMI below 35 kg/m², information from other ratios, such as the ratio of waist circumference to hip circumference also can be useful.

Does obesity cause problems during pregnancy?

Obesity can cause devastating problems during pregnancy with the risk and severity of problems, both for mother and fetus, increasing in proportion to the mothers BMI. Thus, women with Class 3 obesity are at greater risk compared with women with Class 2 obesity, who in turn carry greater risk than those with Class 1 obesity and those in the overweight category.

In all overweight groups (overweight through Class 3 obesity), the risk of developing gestational diabetes is significantly elevated compared with mothers whose BMI is below 25 kg/m².  With increasing obesity the chance of a range of other serious conditions increases, including preeclampsia (a pregnancy condition featuring high blood pressure and protein in the urine) and infections.

Does obesity during pregnancy cause problems for the baby?

Maternal obesity can cause neural tube defects (parts of the babys brain or spinal cord left uncovered), infections, macrosomia (high birth weight), and shoulder dystocia (the fetal shoulder gets stuck in the birth canal, preventing delivery. Macrosomia and shoulder dystocia, in turn, cause an increase in the number of instrumental deliveries (use of devices to pull the baby through the birth canal) and emergency cesarean section in connection with obesity. Obesity also increases the risk of stillbirth, and prior to delivery makes fetal heart monitoring very difficult and sometimes impossible, due to thick layers of tissue between the monitor and the baby. Proportional to BMI, along with neural tube defects, maternal obesity can also cause numerous congenital anomalies of the newborns face, body, heart, and great vessels. The later include problems with the heart valves, the shape of the heart, and a classic combination of four defects known as Tetralogy of Fallot.

What to consider about taking medications when you are pregnant or breastfeeding:

  • The risks to yourself and your baby if you do not treat the obesity
  • The risks and benefits of each medication you use when you are pregnant
  • The risks and benefits of each medication you use when you are breastfeeding

What should I know about using medication to treat obesity during pregnancy?

The most common medications related to obesity during pregnancy are type 2 diabetes medications and medications for high blood pressure since diabetes and high blood pressure both result directly from obesity. Typical medication for type 2 diabetes is metformin. Several studies that have looked at the use of metformin during pregnancy have not found an increased risk of birth defects. However, more studies are needed to determine the exact risk of metformin use during pregnancy. As for blood pressure medication, certain classes of drugs — namely angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, and renin inhibitors — are suspected to be harmful to the fetus, so generally, they are avoided. Since there are numerous types of blood pressure lowering drugs, however, it is possible for your doctors to manage both gestational hypertension (high blood pressure provoked by pregnancy) and high blood pressure that you already had prior to pregnancy. The situation gets more complex when a woman develops high blood pressure as a component of a condition called preeclampsia, which can lead to a need for premature delivery in order to save both mother and child.

As for medications given specifically to treat obesity, as opposed to diabetes or high blood pressure, there are several different drugs that can be given to influence appetite and satiety. These drugs constitute a secondary line of treatment that is given alongside the primary line of treatment, which consists of lifestyle modification. Consequently, there is no one drug that is absolutely critical to an obese patient for the course of therapy. That said, data are very limited when it comes to such drugs. Laboratory animal studies, for instance, suggest that a drug combination called naltrexone-bupropion, which is given to combat food addiction, can lead to pregnancy loss, but there is no verification of this in humans.

Who should NOT stop taking medication for obesity during pregnancy?

Medications comprise a secondary treatment tactic in obesity and it is possible for any patient to stop a particular obesity medication in consultation with her physician.

What should I know about choosing a medication for my obesity during pregnancy?

Each class of medications has benefits and drawbacks, but studies of humans taking drugs designed to reduce hunger and food cravings in obese patients have been limited, especially in connection with pregnancy. It is important to stay in communication with your health care provider as the release of new studies over time can change the outlook on the role of obesity medications during pregnancy.

You may find Pregistrys expert reports about the individual medications to treat obesity here. Additional information can also be found in the sources listed at the end of this report.

What should I know about taking a medication for my obesity when I am breastfeeding?

Data are very limited when it comes to most obesity drugs. However, the drug metformin, which is given for both obesity and diabetes, is thought to be safe during breastfeeding, although there is concern that it could harm newborns who are premature, or who suffer from kidney problems.

What alternative therapies besides medications can I use to treat my obesity during pregnancy?

Actually, the primary treatment for obesity is lifestyle modification. Patients are put on special exercise programs and guided diets. Additionally, for those who are not pregnant, there is an option for bariatric surgery in which parts of your gastrointestinal tract are altered to decrease the amount of food and calories that you absorb with each meal.

What can I do for myself and my baby when I have obesity during pregnancy?

Lose weight by any means that your doctors offer. Even if you are unable to move out of the obesity range, dropping down to a lower class of obesity by lowering your BMI will reduce the risk of severe complications, including preeclampsia (which can cause both maternal and fetal death), and neural tube defects, heart defects, and other serious conditions in the newborn. If you are not pregnant yet, but planning to become pregnant, it is strongly recommended that you reduce your weight prior to becoming pregnant. If you are not yet pregnant, more options will be available to you, including bariatric surgery, and a range of medications, as well as many lifestyle change options.

Resources for obesity in pregnancy:

For more information about obesity during and after pregnancy, contact http://www.womenshealth.gov/ (800-994-9662 [TDD: 888-220-5446]) or read the following articles:

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General information

It is very common for women to worry about having a miscarriage or giving birth to a child with a birth defect while they are pregnant. Many decisions that women make about their health during pregnancy are made with these concerns in mind.

For many women these concerns are very real. As many as 1 in 5 pregnancies end in a miscarriage, and 1 in 33 babies are born with a birth defect. These rates are considered the background population risk, which means they do not take into consideration anything about the health of the mom, the medications she is taking, or the family history of the mom or the baby’s dad. A number of different things can increase these risks, including taking certain medications during pregnancy.

It is known that most medications, including over-the-counter medications, taken during pregnancy do get passed on to the baby. Fortunately, most medicines are not harmful to the baby and can be safely taken during pregnancy. But there are some that are known to be harmful to a baby’s normal development and growth, especially when they are taken during certain times of the pregnancy. Because of this, it is important to talk with your doctor or midwife about any medications you are taking, ideally before you even try to get pregnant.

If a doctor other than the one caring for your pregnancy recommends that you start a new medicine while you are pregnant, it is important that you let them know you are pregnant.

If you do need to take a new medication while pregnant, it is important to discuss the possible risks the medicine may pose on your pregnancy with your doctor or midwife. They can help you understand the benefits and the risks of taking the medicine.

Ultimately, the decision to start, stop, or change medications during pregnancy is up to you to make, along with input from your doctor or midwife. If you do take medications during pregnancy, be sure to keep track of all the medications you are taking.

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