FRIDAY, Sept. 25, 2015 (HealthDay News) -- The plastics chemical BPA appears to be linked with low birth weight among baby girls, a new study reports.
Mothers with high blood levels of BPA early in their pregnancy tended to have newborn girls who weighed less than girls born of mothers with low BPA levels, said senior author Vasantha Padmanabhan, a professor of pediatrics and obstetrics and gynecology at the University of Michigan Medical School.
The researchers found that for every twofold increase of BPA in a mother's blood during the first trimester, the weight of their newborn girls decreased by about 6.5 ounces.
Although the study was able to find an association between BPA and the weight of newborn girls, it's important to note that this study isn't designed to prove a cause-and-effect relationship between those factors.
Padmanabhan pointed out a potential strength of the study: This study is one of the first to evaluate mothers' BPA levels early in the pregnancy, rather than rely on samples from umbilical cord blood following delivery, she said.
"When you are thinking about fetal development during pregnancy, the early period is very critical, when most of the organs are differentiating," she said. "We felt if any chemical is going to have an impact, that would be the time point when you should look at associations."
But a spokesman for the American Chemistry Council, an industry group, says the use of maternal blood samples calls the results into question.
"Experts led by the Centers for Disease Control and Prevention, an authority on biomonitoring, advise against using blood measurements for BPA exposure, stating that 'it is seldom possible to verify that [blood] concentrations of [BPA] are valid measures of exposure,'" Steven Hentges from the American Chemistry Council, said in a prepared statement.
BPA, or bisphenol A, is a chemical used to create plastics and epoxy resins. It can be found in plastic containers, dental sealants and thermal cash receipts, Padmanabhan said. BPA resins also are used to coat the insides of canned foods, to prevent the aluminum from deteriorating, the researchers said.
Prior studies have found that BPA can affect hormones such as estrogen, testosterone, thyroid and insulin, Padmanabhan said. Because of this, concerns have arisen that exposure to BPA in the womb might affect a child's gestation and early development, the researchers noted in background information in the study.
To study the potential effects of BPA during pregnancy, Padmanabhan and her colleagues took first-trimester blood samples from 61 pregnant women being treated at the University of Michigan Von Voigtlander Women's Hospital. They also sampled blood from the umbilical cord during delivery, the study said.
The investigators found that higher BPA levels were associated with lower birth weight in girls, but not in boys. High BPA levels were linked to slightly longer female pregnancies, by about one day, the study found.
Hormones affect boys and girls differently as they grow in the womb, and these differences are likely why only girls appeared to be affected by BPA, Padmanabhan said.
"There are so many differences in hormonal changes that it is hard to pinpoint a particular mediator," she said. "For example, during early development there is an initial surge of testosterone in the male fetuses that doesn't occur in the female."
Based on these and other results, pregnant women should try to limit their exposure to BPA, said Dr. Leonardo Trasande, an associate professor of pediatrics and environmental medicine at NYU School of Medicine in New York City.
"This study adds further concern about the health effects of BPA exposure, particularly in vulnerable populations like pregnant women and children," Trasande said.
Women can avoid BPA exposure by not heating food containers in microwaves, avoiding canned foods, and declining to take paper receipts from cash registers, he said.
However, Hentges countered that "this small-scale study of prenatal exposures provides essentially no meaningful information on the safety of BPA."
Hentges said that BPA is considered a safe chemical by U.S. regulators.
"Based on a large and compelling body of research, government bodies around the world have clearly stated that BPA is safe as used in food contact materials," Hentges said. "In particular, the Food and Drug Administration responded recently to the question 'Is BPA safe?' with one unambiguous word: 'Yes.' Supporting this clear conclusion is one of the largest studies ever conducted on BPA, which was published by FDA researchers early in 2014."
The current study appears in the Sept. 25 Journal of Clinical Endocrinology & Metabolism.
For more about BPA, visit the U.S. National Institutes of Health.