Kira Testin knew that something was wrong before she and her husband ever saw the fertility specialist. ?We had been trying for a year to get pregnant,? recalls Testin, who was 27 at the time. ?We weren?t na?ve, but it still was devastating to hear that we would be unable to conceive naturally.?
For the Testins, in vitro fertilization (IVF) ? when a woman?s eggs are retrieved, fertilized and grown to embryo-stage in a petri dish, then implanted back in her uterus ? was their only chance at pregnancy.
And their chances were low at that. More often than not, IVF takes repeated, costly and heart-wrenching attempts.
Now scientists have found another potential obstacle for would-be parents. New research has turned up evidence of a link between endocrine-disrupting chemicals in the environment and poor IVF outcomes.
Some chemicals in food and consumer products may disrupt a woman?s estrogen, which interferes with her ability to get pregnant. Higher blood levels of pollutants such as bisphenol A (BPA), polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) have been found in mothers with failed IVF attempts, according to a handful of recent studies.
The Testins, from a small town near Milwaukee, Wis., are among an estimated 9 million U.S. couples ? one out of every eight ? who are infertile, according to the American Fertility Association.
Causes of infertility are numerous, ranging from hormonal imbalances, to defects of the uterus, to misshapen sperm, low sperm count or low sperm motility in men.
Some scientists now theorize that endocrine-disrupting chemicals in the environment also can reduce fertility. Endocrine disruptors are a class of more than 1,200 chemicals that can mimic or block hormones, including estrogen, the primary female sex hormone involved in pregnancy.
?These chemicals may affect the way hormones regulate many aspects of our bodies, potentially even the ability to get pregnant,? said Laura Vandenberg, a reproductive scientist at Tufts University.
In one study of 765 women who underwent a total of 827 IVF cycles at Boston area clinics, researchers found an association between blood PCB concentrations and the rate at which embryos successfully attached or implanted to the uterine wall. The study was published in July in the journal Environmental Health Perspectives.
The odds of failed implantation doubled among women with the highest blood level of PCB-153 (the form of the chemical, on average, present in the highest concentration) compared to women with the lowest levels. Women with the highest levels were also 41 percent less likely to give birth to a live infant than women with the lowest blood levels.
Perhaps the most surprising finding ? even low levels of PCBs, the same as those found in the general U.S. population, were associated with adverse early pregnancy outcomes in IVF, said Dr. Russ Hauser, professor of environmental and occupational epidemiology at Harvard School of Public Health and co-author of the study.
The same researchers also reported a link between another long-banned pollutant, hexachlorobenzene (HCB), and implantation failure, in a paper published online in Environmental Health Perspectives in August.
PCBs and HCB are both long-lived pollutants that accumulate in food chains and take decades to break down. Animal studies have shown that both types of compounds can mimic or block hormones. Hauser said there is evidence that HCB suppresses a hormone called luteal progesterone, which is important for egg implantation.
PCBs ? a class of industrial chemicals used mostly as insulating fluids for electrical equipment ? have been banned in the United States as well as in most other developed countries for more than 30 years. However, because of their extensive use and long half-life, human exposure remains widespread. In fact, studies have shown that more than 95 percent of Americans older than 12 still have detectable levels of PCBs in their blood. Humans are exposed mainly through food.
Source: http://rss.sciam.com/click.phdo?i=55ccb1e8af3a25855eef3d78923cd98b
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