Endometriosis Causing Infertility
Frederick R. Jelovsek MD
How endometriosis causes infertility is not fully known. Most physicians believe that endometriosis affects fertility only when the endometriotic lesions cause scarring. This scarring in turn decreases the ability of the fallopian tube to pick up an egg where it will be fertilized by the sperm and transported to the inside of the uterus for implantation. The more extensive the scarring, i.e., the more severe the endometriosis, the more likely for infertility to be caused by the endometriosis.
In the process of in-vitro fertilization (IVF), the normal mechanisms of fertilization are bypassed because the egg is harvested from the ovary just prior to ovulation. It is then put in a "test tube" with sperm where fertilization takes place instead of in the fallopian tube. The fertilized egg is then implanted inside the uterus through the vagina and cervix rather than by way of the fallopian tube. One would expect IVF patients with endometriosis to fertilize and get pregnant at all the same rate regardless of the severity of their disease, since the transport system is being circumvented in IVF.
This was not totally the case according to Pal and others. In this recent study, Pal L, Shifren JL, Isaacson KB, Chang Y, Leykin L, Toth TL: Impact of varying stages of endometriosis on the outcome of in vitro fertilization-embryo transfer. J Assist Reprod Genet. 1998; 15(1): 27-31, they found that patients with more severe endometriosis had eggs that didn't fertilize as well (in the "test tube") as did those from patients with milder disease. The number of eggs that were stimulated and harvested in each group were the same and the fertilized eggs that were transferred to the uterus and subsequently developed were the same in both groups. The only difference was that in patients with mild endometriosis, more of their eggs were fertilized than in patients with more severe (Stage 3 and 4) endometriosis.
This study suggests that there is a biological impact of some sort on the eggs (while still in the ovary) by severe endometriosis that makes the "less fertilizable". It may be that IVF may compensate for or overcome this reduction in the biological potential of the oocytes associated with severe disease if multiple eggs are obtained.
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