BMI At The Start Of Pregnancy Is Linked To Birth Outcomes, New Study Finds

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For women who are just starting their journey into pregnancy and motherhood, there's a lot of conflicting information out there, and a good many strangers on the internet always seem more than willing to dole out all kinds of advice. When it comes to a mom's weight at the start of her pregnancy, there's a lot of differing opinions about what's best for both mom and baby — but one recent study found that woman's BMI at the start of pregnancy could be linked to certain birth outcomes, and that more women are entering pregnancy underweight and overweight than before.

The study, conducted by the Centers for Disease Control and Prevention, looked at the pre-pregnancy weights of women across the United States and noted that more women were entering pregnancy either under- or overweight in recent years. Using body mass index — which measures people's body fat as a proportion of height and weight — as a guide, the CDC looked at the number of women giving birth either underweight (with a BMI below 18.5) or overweight (with a BMI over 25) in the country.

As it turns out, the United States is moving from the Department of Health and Human Services' Healthy People 2020 initiative goals for pregnancy: in 2007, 52.5 percent of American women were entering pregnancies at a "healthy" weight (with BMIs between 18.5 and 25), a percentage that the federal government wanted to increase by 2020. But by 2015, the needle had actually swung the other way, with only 45 percent of women entering pregnancies at BMIs between 18.5 and 25.

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Beginning a pregnancy underweight, according to the CDC, is linked to babies born small for their gestational age, while starting a pregnancy overweight is linked to a higher risk of cesarean delivery, babies larger than their gestational age, and childhood obesity. (Other studies, it should be noted, have failed to prove a link between childhood obesity and pregnancy BMI.)

A person's health can, of course, affect their pregnancy — that's why prenatal vitamins are a thing and why pregnant vegans just can't catch a break. But it's important to note that researchers have generally started moving away from BMI as a health marker, according to TIME, since it doesn't take into account muscle mass versus fat, nor does it differentiate between different kinds of fat (some of which can be more harmful to one's health).

Anyone who is worried about being under- or overweight at the start of their pregnancy should speak to their doctor. Eyeing up height and weight alone isn't the most effective tool out there, and a doctor will be able to take into account all of a patient's relevant details when it comes to judging their health. That means not just a person's body mass index, but their blood levels, nutrition, exercise habits, and more.

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Encouraging more people to go check in with their doctors before pregnancy is, essentially, what the CDC recommends thanks to its findings. "BMI screening during routine clinical visits provides opportunities to address underweight or obesity, promote normal weight upon entering pregnancy, and ultimately help optimize maternal and child health outcomes," the study authors wrote in their analysis of public health implications.

Checking in pre-pregnancy isn't always possible, of course, considering that nearly half of all pregnancies in the United States are unintended. But if you have concerns about weight before or after becoming pregnant, your doctor should definitely be the person you check in with. If there's anything to address to help you get a little healthier during your pregnancy, they can help you plan a healthy way to get there.

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