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Twins Separated at Conception

A blog by Art Castelbaum, MD, Reproductive Medicine Associates of Philadelphia & Central PA, July 25, 2014

I frequently receive pictures and cards from patients who have successfully undergone fertility treatment. My favorite card to receive is a picture of an older and a younger child. In a sense, they were twins separated at conception. The older child was the product of a fresh In Vitro Fertilization (IVF) embryo transfer. The younger child was the result of a cryopreserved embryo from that same IVF cycle that was subsequently used in a frozen embryo transfer cycle.

The majority of women under the age of 35 will have sufficient embryos available during their fresh IVF cycle so that extra embryos can be frozen. By using a more sophisticated freezing technology called vitrification, frozen embryos can be viable for many years. In my personal experience, the longest period during which embryos that were frozen resulted in children was nine years.

Most couples use their frozen embryos when their youngest child is a year or two old. Excellent frozen embryo transfer pregnancy rates can be achieved using a patient’s own natural cycle if she ovulates every month. Alternatively, oral estrogen can be used for two weeks to prepare the lining of the uterus. Because of the advancement in freezing technology and the effectiveness of frozen embryo transfer procedures, I do not recommend transferring more than a single frozen blastocyst embryo for women under age 35 or two blastocyst embryos under age 41.

The last 30 years have seen a dramatic increase in the incidence of twin and triplet pregnancies in the United States. Fertility doctors have been largely responsible. 1 in every 30 infants born in 2009 was a twin; double that of 30 years ago. The serious risks of triplet pregnancies are generally well understood. Most people, however, believe that twins do great. Surprisingly, 25% of twins require neonatal intensive care hospitalization, and the risk of cerebral palsy and even death are higher for twins compared to a single baby. Transferring a single blastocyst embryo avoids these complications.

Furthermore, several recent studies have suggested children conceived with frozen embryos may have better health compared to those conceived during a fresh cycle. I think it is too early to tell whether the findings in this study are correct and that larger, longer term studies are necessary. However, this study does give us confidence that the use of frozen embryos as a routine part of fertility treatments is an excellent option.

Dr. Castelbaum is one of seven world-class fertility specialists at Reproductive Medicine Associates of Philadelphia and Central Pennsylvania. He has been featured in Philadelphia Magazine and on The Discovery Channel and he also serves as a reviewer for the journals Fertility and Sterility and Human Reproduction.


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