Infertility and Multiple Pregnancy: Can you have too much of a good thing? by Serena Chen, M.D.


Infertility and Multiple Pregnancy: 
Can you have too much of a good thing? 
by Serena Chen, M.D.

In general, the best way to reduce multiple births is to transfer only single embryos. In order to do that without dramatically lowering the overall pregnancy rate, implantation rates need to be increased. Implantation rate is the potential of a single embryo to result in a pregnancy and is calculated by taking the total number of gestational sacs divided by the total number of embryos replaced. Implantation rate is always lower than the pregnancy rate because the vast majority of IVF procedures involve the transfer of more than one embryo. The higher the implantation rate, the lower the number of embryos needed to achieve pregnancy, and the lower the multiple birth rate.

Improvements in various techniques used in the laboratory have led to gradually improving pregnancy rates across the country. Improved techniques of embryo culture, assisted hatching and fragment removal are being used more widely. As embryologists gain experience, implantation rates have improved. Again, improvements in implantation rates will ultimately allow physicians to replace fewer and fewer embryos, maintain or improve the overall pregnancy rate and someday, eliminate the risk of high order multiple pregnancy.


Cryopreservation or freezing of embryos is another technique that can be used to reduce multiple births. Cryopreservation is widely available and can help decrease the pressure to transfer large numbers of embryos by allowing a couple to freeze extra embryos for use at a later date. The disadvantages of cryopreservation are that some embryos will not survive the freeze-thaw process and previously frozen embryos may have less pregnancy potential than "fresh" embryos. However, there does not appear to be any increase in the rate of birth defects or miscarriages in pregnancies conceived using frozen-thawed embryos. As this technology continues to improve, with better freeze-thaw survival rates and better pregnancy rates, it will become a more powerful tool to help reduce multiple births.


Preimplantation genetic diagnosis (PGD), or the genetic analysis of embryos prior to transfer into the body is an exciting new technology that could help reduce multiple births. PGD can be used to look for chromosomal aneuploidy (abnormal numbers of chromosomes) in the embryo. This condition can lead to infertility, miscarriages and birth defects (an extra chromosome 21 causes Down's Syndrome). As a woman gets older, the chance that her embryos are chromosomally abnormal increases dramatically. In older women, the ability of the embryologist to select the embryos most likely to result in a pregnancy decreases markedly. This occurs because a higher proportion of the embryos are chromosomally abnormal and because most chromosomal abnormalities do not cause any changes in the embryos appearance. So a very high quality embryo can be very abnormal genetically. Because of the higher rate of chromosomal abnormalites, the implantation rate of the embryos decreases. By using PGD to select the chromosomally normal embryos, the implantation rate of the embryos that are selected is increased. The higher the implantation rate, the lower the number of embryos needed to achieve pregnancy and the lower the multiple birth rate. At this time, PGD can analyze only a limited number of chromosomes and only a few centers worldwide have significant experience in this technique. However, studies performed at Saint Barnabas have already demonstrated that PGD can improve pregnancy rates in women over 35, and dramatically lower the miscarriage rates. Ultimately, as the technique improves, PGD may allow us to offer all patients a single embryo transfer, eliminating the multiple pregnancy problem without sacrificing a high pregnancy rate.


Despite what many infertile couples think, it is possible to have too much of a good thing. Multiple pregnancies involve reward and risk. High order multiple pregnancy can result in serious complications for both the mother and the babies. There are various techniques available to try and minimize these risks. Couples should discuss these techniques with their doctor to decide how or whether to use them in their individual treatment plan.


Serena Chen, M.D. is Director, Division of Reproductive Endocrine Department of Obstetrics and Gynecology Saint Barnabas Medical Center and the Director, Ovum Donation Institute for Reproductive Medicine and Science at Saint Barnabas East Wing Suite 403 94 Old Short Hills Road, Livingston, NJ 07039
Tel 973 322 8286. Email Dr. Chen


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