Last night I became inspired to get our Christmas lights hung up before the weather turned cold again when I would be risking frostbite to complete the job. So I got the bags of lights down from their perch in the unfinished part of my basement and began the job of sorting through which strings lit and which ones did not. Just as soon as one strand lit up it seemed that another winked out. Finally, I had enough to start the job and I managed to string up an assortment of white and colored lights in some semblance of symmetry. Just when I thought I had completed the task the corner outlet in my garage blew... Suddenly there was a cry from inside the house "what the %#&*$# happened to the Internet! I have to finish my homework! Dad!" So I moved to Plan B. Run an extension cord from the backyard to the garage. Hook up a surge protected power strip. Plug in the power to the internet box and voila...another crisis averted. But a new problem had arisen: the blown outlet. Ugh. An hour later I finally figured out how to reset the GFI and we were back in business.
In reproductive medicine sometimes we fix one issue only to find ourselves confronted by another. Let's consider preimplantation genetic screening (PGS) for IVF. Using PGS we can now determine within 18 hours following an embryo biopsy whether or not that embryo contains a normal number of chromosomes. Since many embryos are missing a whole chromosome (Monosomy 7) or have an extra chromosome (Trisomy 18) we can now elect to only transfer normal embryos. The use of PGS will not change the ultimate delivery rate (if there is a good embryo somewhere in the bunch then we will eventually find it) but it will decrease the rate of miscarriage since most pregnancy losses are genetic in etiology.
So if we only transfer genetically normal embryos then the pregnancy rate should be 100%...right? Except that it isn't. So just like my experience with hanging the lights, once one issue is resolved other issues may arise. For example, just because an embryo has the normal number of chromosomes doesn't mean that it is completely healthy. That embryo may have other problems including single genes that are failing to work correctly. In addition, besides the embryo there could be issues with the embryo transfer (glob of mucus on the catheter) or a difficult navigation of the cervical canal. Finally, the uterus itself may not be receptive to implantation. So even after eliminating genetic issues we still have to sort through other possible explanations for failure. But there is always hope for ultimate success, just sometimes it takes some creative electrical engineering to get everyone back online and sometimes it takes some creative thinking to get those embryos to stick!