There is a whole host of research out there
examining the effects of Bisphenol A (BPA) on reproduction both in vitro (a.k.a. in the lab) and in vivo in various species of
animal. Though one can often translates
the effects of in vitro studies and in vivo studies on animals to how things
might happen in humans, however, this is not always the case. Therefore, there is a need to provide
evidence in the human body prior to making sweeping judgments on the results
based on effects seen in other animals or in the test tube.
In the mouse model, studies have shown that exposure
to BPA at doses known to be present in the environment increases oocyte
aneuploidy, which may result in miscarriage or severe birth defects. Further studies elaborate on the mechanism
behind this error in chromosome distribution in egg cells showing that BPA
contributes to increased aneuploidy by disrupting meiotic spindle formation, as
well as centrosome behavior and chromosome alignment and subsequent
division. Adding to the list of negative
reproductive effects in animal models, BPA has been shown to inhibit the
production of the natural hormone, estradiol, as well as negatively impacting
fertility in general.
What
about human studies?
Preliminary studies looking at the effects of BPA in
humans, specifically in the area of in vitro fertilization (IVF), have shown
that there may be significant negative relationships between BPA levels in
urine and decreases estradiol and numbers of eggs retrieved at the finale of
the IVF retrieval process. There have been
very few studies directly examining the effects of BPA on women undergoing the
IVF process, in particular the associations between BPA and early reproductive
outcomes, oocyte quality, and early embryonic growth (i.e. cleavage) rates.
Just last year, a group at Massachusetts General
Hospital in Boston, MA, a teaching
hospital affiliated with Harvard University, set out to determine how BPA
influenced the IVF process, in particular effects on the quality of the egg and
developing embryo, as well as fertilization rates and cleavage rate of the
developing blastocyst.
The MGH team looked at a group of women undergoing
IVF procedures using their own eggs (i.e. not donor eggs) and analyzed the
levels of BPA present in their urine.
Additionally, they were asked general questions about demographics,
medical history, lifestyle, and finally occupational history. On the day of egg retrieval, the number of MII
oocytes as well as the percentage of mature oocytes from all of the oocytes
collected during the retrieval (i.e. maturation rate) were measured or calculated. The fertilization rates of these mature
oocytes were also calculated.
After fertilization was complete, the quality of
embryos on Day 5 of development was determined by counting the number of cells
present in the developing blastocysts.
BPA
& IVF = A Match Made in Hell?
What the team at MGH found in these women undergoing
IVF treatment for their infertility was that BPA levels in urine resulted in a
fewer number of oocytes retrieved per IVF cycle, as well as a decreased level
of estradiol on the day of HCG (human chorionic gonadotropin)
administration when estradiol levels should be at their peak. Earlier studies in IVF research have shown
that serum estradiol levels and the number of oocytes retrieved per IVF cycle
are strong predictors of IVF success in humans.
Specifically, the MGH researchers found that there
was a significant drop in the numbers of mature oocytes as well as the number
of normal oocytes successfully fertilized during the IVF process, which were
both correlated with BPA levels in the urine.
In terms of embryo quality, no significant associations were noted in
terms of embryo quality and BPA levels in urine, however, the team at MGH
stressed that this result may be bias due to the nature of their experimental
design. This question remains to be
answered and would be an important focus for future research.
Overall, the results of this trial were disconcerting
for those undergoing IVF treatment. If
you were exposed to a higher level of BPA, you may have a much harder time
getting pregnant not only by natural methods, but also by IVF
intervention. With increased BPA levels
in the body, the sheer number of mature eggs ready for fertilization is lower
than it would be normally, and estradiol, a key hormone during the maturation
and fertilization processes, is also significantly lower in concentration due
to this BPA exposure.
Could it be that BPA may be both causing infertility
as well as preventing the current IVF fertility treatments from
succeeding? Certainly more needs to be examined
here, but from this study it seems to be clear that higher BPA levels present
in the urine of women undergoing IVF treatment are at a significant disadvantage
to successfully conceiving than their counterparts that have not been exposed
to the endocrine disrupting BPA.
Source: Ehrlich, S., Williams, P.L., Missmer, S.A.,
Flaws, J.A., Ye, X., Calafat, A.M., Petrozza, J.C., Wright, D., and Hauser, R.
2012. Urinary Bisphenol A
concentrations and early reproductive health outcomes among women undergoing
IVF. Human Reproduction 27(12):3583-3592.
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