Weight Gain During Pregnancy: 2nd Trimester May Be Key

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The second trimester of pregnancy may be a crucial period of time for women to stick to weight-gain recommendations, a new study says.

Overweight or obese women who gained an excessive amount of weight during the second trimester had a greater than 90 percent chance of gaining too much weight by the end of pregnancy, the study found.

The findings suggest that interventions to keep pregnant women on track to meet the recommended weight-gain guidelines could be started as early as the second trimester.

"If you tell somebody, 'you should have put on less weight [in pregnancy],' it doesn’t help the person very much," said study researcher Rüdiger von Kries, of the Institute of Social Pediatrics and Adolescent Medicine at the Ludwig-Maximilians University Munich in Germany. The new finding identifies the problem (too little or too much weight gain) at a time when a woman can still do something about it, von Kries said.

The amount of weight a woman should gain in pregnancy depends on her starting weight. The Institute of Medicine recommends normal-weight women gain 25 to 35 pounds during pregnancy, underweight women gain 28 to 40 pounds, overweight woman gain 15 to 25 pounds, and obese woman gain 11 to 20 pounds.

By the end of the second trimester, the IOM recommends normal weight women gain no more than 20 pounds, and obese women gain no more than 10 pounds.

Dietary advice given in mid-pregnancy could increase weight in women with inadequate pregnancy weight gain, and physical activity and weight monitoring could reduce weight in women with excessive pregnancy weight gain, the researchers said.

In the new study, researchers gathered information from 7,962 pregnant women living in Germany. The researchers used medical records to obtain the women's pre-pregnancy weight, as well as the course of their weight gain during pregnancy. They used the Institute of Medicine guidelines to calculate the amount of weight each woman should have gained in each week of pregnancy, depending on her starting weight (the rate of weight gain is slower in the first trimester, compared with the second and third.)

Normal-weight women who gained too much weight in the second trimester had a 74 percent chance of gaining too much weight by the end of their pregnancy, the results showed.

Underweight women who gained too little weight during the second trimester had a 72 percent chance of gaining too little weight by the end of their pregnancy.

Overweight women who gained too much weigh in the second trimester had a 94 percent chance, and obese women a 93 percent chance, of gaining too much weight by the end of pregnancy.

Too little weight gain in pregnancy can lead to complications such as preterm birth and small-for- gestational-age infants, while too much weight gain in pregnancy can lead to gestational diabetes as well as an increased risk of health problems for the child, such as childhood obesity, according to the Mayo Clinic.

The study was published online May 2 in the American Journal of Clinical Nutrition.

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Rachael Rettner
Rachael Rettner
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.