Excess Pregnancy Weight Increases Risk Of Birth Defects, Study Finds

Excess Pregnancy Weight Increases Risk Of Birth Defects, Study Finds

Women of childbearing age are entering pregnancy with a higher body mass index (BMI) than ever before.

Western countries have been facing an obesity crisis for decades.

It’s particularly important healthcare providers, public health officials and researchers understand the potential complications of excess weight during pregnancy.

Excess Pregnancy Weight Increases Risk Of Birth Defects, Study Finds

There are many possible reasons for a high BMI. It’s also important to note BMI alone isn’t always an accurate measure of health; other clinical information should also be taken into account.

BMI is, however, a useful piece of the puzzle, in terms of research and public health.

A recently published study found the risk of major birth defects increased in step with the level of a mother’s obesity or overweight status.

How Does Maternal Weight Affect Baby’s Risk Of Birth Defects?

When looking at the entire population, it’s important to note a certain percentage of babies will have birth defects. When we break down the risk of birth defects according to demographics, certain factors are linked with increased risk.

An increased risk isn’t a guarantee; it simply means certain factors increase the percentage of babies with birth defects in various groups. Increased risk can often mean there’s a correlation but not necessarily a clearly defined cause. In some cases, there’s no known cause.

According to lead researcher, Martina Persson, of the Karolinska Institutet in Stockholm, Sweden, the study’s findings are not entirely new but “expand on previous knowledge”.

Previous research had shown maternal obesity increased the risk of congenital malformations (birth defects). However, previous studies hadn’t discovered whether the severity of obesity or overweight status affected risk level, or whether simply being overweight indicated risk level.

This study found the risk of birth defects increased in step with the severity of obesity or being overweight.

Researchers looked at 1.2 million live, singleton births from 2001 to 2014.

The study defined the groups as follows:

BMI under 18.5 – Underweight
BMI of 18.5 to 24 – Normal weight
BMI of 25 to 29 – Overweight
BMI of 30-34 – Class I obesity
BMI of 35-39 – Class II obesity
BMI of 40 or more – Class III obesity

When they looked at the data they found:

  • 43,550 infants (3.5% of those in the study), had a major congenital malformation
  • Heart defects were the most common, but other malformations included defects of the genital organs, limbs, digestive system, nervous system, and urinary systems.
  • Babies of mothers in the normal weight range had a 3.4% risk of major malformations.
  • The risk of birth defects in the overweight range was 3.5%.
  • In the Class I obesity group the risk was 3.8%.
  • In the Class II obesity group the risk was 4.2%.
  • In the Class III obesity group the risk was 4.7%

Based on these results, Persson said, “We demonstrate increased risks of major malformations also in offspring of mothers with overweight, and risks progressively increase with a mother’s overweight and obesity severity”.

Importantly, she noted while the results show a connection, they can’t prove a direct cause between maternal weight and birth defects.

Does Being Overweight Or Obese Increase Serious Risks For My Baby?

In short, several studies have noted increased risks associated with high maternal BMI. However, although the risk is increased, if we look at even the highest risk (4.7%), it still means 95% of babies born to the mothers in the Class III obesity group didn’t have major congenital malformations.

So, there are associated increased risks but a risk certainly isn’t a guarantee. In addition to the risk of malformations, there are other risks. Some of them are associated with gestational diabetes (GD), which is more likely in women with a higher BMI, and long-term metabolic issues based on maternal diet.

“Overweight and obesity in pregnancy increase risks of several severe complications in the mother and her child”, Persson said. It’s important we’re aware of these risks and work to reduce them.

Another important note: other research has found it might not necessarily be a woman’s weight that increases her pregnancy risks, but her care providers’ attitude to it.

Are Maternal Weight Studies Necessary?

There’s nothing quite like the pressure of having a baby. You want to be sure you’re doing the best you can to give your baby their best start possible.

Weight can be a very sensitive topic, especially for women doing their best to have a healthy lifestyle but still struggling to reach what their healthcare providers consider a healthy weight (a common struggle for women with PCOS or hypothyroidism).

No mother-to-be, or woman trying to conceive, should be treated poorly by her healthcare provider or researcher. She should certainly not be judged, based on her BMI.

Research into maternal weight, however, is an important part of maternity care.

When we’re aware of risk factors, we can work to reduce them. If we’re unable to reduce risk, then at least knowing about potential risks allows healthcare providers to monitor for complications and catch them as early as possible.

What Are The Benefits Of A Healthy Weight?

As noted above, in an assessment of a person’s health, BMI is simply a piece of the puzzle. Your individual build, muscle mass, etc. can all affect your BMI.

For some people, a BMI measurement provides insight into their weight. Other research suggests it’s more accurate to look at a person’s waist-to-height ratio.

When it comes to pregnancy, a healthy weight can benefit both mother and baby.

Dr. Raul Artal, Professor and Chairman Emeritus of the Department of Obstetrics, Gynecology and Women’s Health at Saint Louis University, and a maternal fetal medicine specialist (high-risk obstetrics), said obese, overweight and sedentary women “have a very high incidence of diabetes and high blood pressure in pregnancy. As a result, their offspring are at very high risk for certain congenital malformations that come along with obesity”.

This means being at a healthy weight has the benefits of reducing risks of:

  • Congenital heart diseases – by far the most common birth defect among mothers who are obese and have diabetes, according to Artal
  • Neural tube defects, such as spina bifida and hydrocephalus
  • Limb reductions or absence
  • Preterm birth

Being at a healthy weight also has benefits for the mother. It reduces the risk of pregnancy and birth complications, high blood pressure, gestational diabetes, and other complications that increase the risk of requiring an induction or c-section birth.

Regardless of risks factors, as noted above, it’s important to remember this: in a general population there is still the risk of congenital malformations. Statistically, there is increased risk with higher maternal BMI, but certainly no guarantee; neither is there a clear-cut causation.

What Does All Of This Information Mean For Mothers?

This information is meant to help health care providers and mothers make educated decisions about health care, prevention, nutrition and lifestyle.

If you’re planning a pregnancy, an important part of that is to work towards a healthy lifestyle. Regardless of your current BMI, being active and having adequate nutrition, with limited processed foods, can help you prepare for pregnancy.

If you’re already pregnant, staying or getting active, and eating a diet of healthy whole foods is an important part of prenatal care.

Maternal weight is one piece in the puzzle of a healthy pregnancy. There are risks associated with an increased maternal weight, but it isn’t a guarantee you will have complications.

Use the information to make the healthiest choices you can, and be sure to choose a maternity care provider who is respectful and helpful in meeting your pregnancy goals.

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Maria Silver Pyanov is a mama of four energetic boys and one unique little girl. She is also a doula and childbirth educator. She's an advocate for birth options, and adequate prenatal care and support. She believes in the importance of rebuilding the village so no parent feels unsupported.

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