Field Notes

PCBs May Affect In Vitro Fertilization Outcomes

According to a new study published in Environmental Health Perspectives, serum polychlorinated biphenyls (PCBs) at concentrations found in the general U.S. population are associated with the failure of fertilized embryos to implant in the uterus after in vitro fertilization (IVF). This study may help explain earlier reports of impaired reproduction and increased time to pregnancy among women exposed to PCBs.

“Our findings provide insight into a specific time point following conception that determines whether a pregnancy will occur that may be particularly sensitive to PCB exposure,” says lead author John Meeker, ScD, CIH.

PCBs were banned in the United States and other developed countries in the 1970s, but they persist in the environment due to prior widespread use and resistance to breakdown. Exposure to PCBs occurs mainly through contaminated foods and is associated with adverse health effects, including negative impacts on reproduction.

By conducting the current study with women undergoing IVF, the researchers could examine events during early pregnancy that are difficult or impossible to assess in the general population. “Not only do couples undergoing assisted reproduction represent a growing proportion of the population, but they also provide a unique opportunity to study factors related to very early [pregnancy] losses that usually go undetected and contribute to fertility issues,” Meeker says.

The women were recruited between August 1994 and June 2003. Blood was collected before each woman’s IVF attempt, and concentrations of 57 individual PCBs were measured in the women’s serum. Among 765 women and 827 IVF cycles, there were 286 live births and 530 pregnancy losses. The losses included 229 implantation failures, 177 very early miscarriages (or “chemical pregnancies”), and 124 later miscarriages.

In their analysis, the researchers examined the associations between IVF outcomes and concentrations of individual PCBs known as congeners 118, 138, and 153, as well as the sum of all congeners. PCBs were also grouped according to their structure and biological activity.

After controlling for confounders, the researchers found that implantation failure was twice as likely in women with the highest exposures to PCB-153 and total PCBs than in women with the lowest exposures. The odds of a live birth were reduced by more than 40% in these women.

The strengths of this study are its prospective design, detailed clinical data, the relatively large number of observations, and the fact that the researchers were able to directly measure women’s PCB levels, which reflected exposures consistent with those in the general population. Limitations include the possibility that women undergoing IVF have a different response to PCBs than women in the general population and the lack of exposure data on the women’s partners.

Coauthor Russ Hauser, MD, notes, “Early pregnancy end points were shown in experimental animals to be more sensitive than later end points. Therefore, IVF as a model to study the impact of environmental chemicals on early pregnancy is the only way we can observe these end points in women.”

— Source: Environmental Health Perspectives

 

People With Diabetes Are Not Benefiting From Advances in Kidney Care

Despite significant advances in kidney care over the past 20 years, efforts to improve therapy for type 1 diabetes patients with kidney dysfunction remain unsuccessful, according to a study in the Journal of the American Society of Nephrology. The results suggest that more effective therapies are needed for these patients.

One in three patients with type 1 diabetes develops a condition called macroalbuminuria, in which especially high amounts of protein are lost through the urine. Patients with type 1 diabetes and macroalbuminuria face increased risks of developing kidney failure or end-stage renal disease (ESRD) and of dying from heart-related causes.

Andrzej Krolewski, MD, PhD, of Joslin Diabetes Center and Brigham and Women’s Hospital, and colleagues studied these risks in patients at the Joslin Clinic. Between 1991 and 2004, the investigators enrolled 423 white patients with type 1 diabetes who developed macroalbuminuria. Ninety-eight percent of patients were followed through 2008; ESRD developed in 172 patients and 29 died without ESRD. The majority of these outcomes occurred between the ages of 36 and 52 with durations of diabetes of 21 to 37 years.

During the more than 15 years of follow-up, the use of treatments to protect the kidneys increased from 56% to 82% and blood pressure and cholesterol levels improved significantly. However, the risks of both ESRD and pre-ESRD death did not change over that time. There were 70 post-ESRD deaths and the mortality rate was very similar during the 1990s and the 2000s. Throughout the study, patients who received preemptive kidney transplants (before dialysis) were less likely to die.

“Our findings clearly indicate that the accomplishments in treatment of patients with type 1 diabetes and macroalbuminuria over the last 20 years are not effective enough, and more effective therapies to retard progression to ESRD are desperately needed,” says Krolewski. “New therapies need to be developed, including more aggressive or experimental protocols to stop or retard declining renal function, which leads to ESRD.”

— Source: American Society of Nephrology