Girls born to mothers with high levels of BPA in their systems during the first trimester of pregnancy weigh less at birth than babies with lower exposure, according to a new study released last week. The study adds to evidence that fetal exposure to the ubiquitous chemical bisphenol-A (BPA) may contribute to fetal developmental problems. Low birth weights are linked to a host of health problems later in life, such as obesity, diabetes, infertility, and heart disease.
Researchers tested mothers' blood during their first trimester and at delivery for BPA, and tested umbilical cord blood after delivery. They tested for both BPA and "conjugated BPA," the form BPA takes after the body processes it. Bottom line: more BPA in women's blood meant babies weighed less. For every doubling in free, or unconjugated, BPA in the mothers' first-term blood, babies weighed, on average, 6.5 ounces less. The research was published in The Journal of Clinical Endocrinology & Metabolism.
Similarly, for every doubling of free-BPA in the woman's blood at birth, babies weighed on average 3 ounces less. "Having small babies at birth is a risk factor for a whole bunch of different things," said Laura Vandenberg, assistant professor of environmental health at the University of Massachusetts, Amherst who was not involved in the study.
Another recent study from China found BPA levels in mothers' urine was linked to low birth weights. That study also found a much stronger association with baby girls.
Unfortunately for pregnant women, BPA — used to make polycarbonate plastic and found in some food cans and paper receipts — is found in most people. Earlier this year, California mandated warning labels for products made with BPA. And in 2011, the state banned BPA in baby bottles and sippy cups, but the chemical is still widely used in food containers. In fact, even the most diligent mothers-to-be may find it challenging to avoid contact with BPA.
The strong link between fetal exposure to BPA during the first trimester and birth weights makes sense, said Vasantha Padmanabhan, senior author of the study and professor of pediatrics, obstetrics and gynecology, molecular and integrative physiology, and environmental health sciences at the University of Michigan. "When you think about development, early in the pregnancy is a critical time — when fetuses are most sensitive to insults such as stress, environmental chemicals — that's why we looked at the first trimester," she said.
About 8 percent of babies born in the United States suffer from low birth weights, considered less than 5.5 pounds, according to the US Centers for Disease Control and Prevention. Other possible contributors to low birth weights include smoking or drinking alcohol during pregnancy, mothers' lack of weight gain, mothers' age, and stress.
The University of Michigan study doesn't prove BPA caused low birth weights. But it could play a role, as the chemical mimics hormones and can disrupt endocrine systems. Even though BPA clears from the body quickly, scientists suspect it could bind to receptors or could be stored in fat for release later. Proper functioning of these receptors is critical to organ development and function.
The American Chemistry Council, which represents chemical manufacturers, said the study provides "no meaningful information on the safety of BPA." The council has defended BPA as safe as used in food packaging. Steve Hentges, a representative of the council, called into question using blood to measure BPA exposure. He also suggested that BPA from another source contaminated the blood samples.
Padmanabhan said the study and BPA measurements "represent a true life scenario," because blood was drawn with a researcher present to ensure no plastic contact.
The researchers did not find a link between BPA levels and baby boys' weights. It's not clear why the exposure was only linked to lower birth weights in girls, but the work suggests that females might be more susceptible to BPA exposure before birth.
In the recent Chinese study, which ran from 2012 to 2014, researchers selected 452 mother-infant pairs from Wuhan, the most populous city in Central China. They collected urine samples from the mothers at delivery and measured for BPA. Using birth weight data obtained from medical records, the researchers then evaluated the relationship between urinary BPA levels and low birth weight.
They found that mothers of newborns with lower birth weights had significantly higher BPA levels in their urine than the control mothers, according to the study published in Environment International. They also found that the association between low birth weight and higher BPA levels was more pronounced among baby girls, which also suggested that female babies might be more susceptible to BPA than males.
The Chinese study also didn't prove BPA caused the low birth weights. But in 2013, findings from a Dutch study suggested that BPA exposure at levels commonly found in people may slow fetal growth. In addition, a 2014 study linked high BPA levels in the placenta to lower birth weights.
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