One or Two?
There’s been a lot of press the past few weeks about single embryo transfer. Single embryo transfer is not anything that’s new. Europeans have been advocating single embryo transfer for almost a decade. In The USA, around 10% of IVF cycles utilize single embryo transfer. My OB colleagues who deliver babies would agree that the biggest complication that arises after infertility treatment is as a result of twin pregnancy. Twins had become so commonplace that we no longer turn a head when we see a stroller with twins in the grocery store or the shopping mall. It is true that most of these pregnancies result in healthy babies, although there are often complications along the way. Twin pregnancies are harder on moms, harder on babies and harder on the obstetrician to care for them.
Having one baby at a time sounds great, but the best way to accomplish this in infertility treatments like IVF is to transfer only one embryo at a time. This sounds perfectly plausable in theory, but single embryo transfer results in fewer pregnancies after IVF. Transferring two embryos gives us more positive pregnancy tests. Unfortunately, it’s a big reason the twin rate is so high. Triplets and quadruplets are fairly rare after IVF because putting back more than 2 or 3 embryos is rare. Yet, putting back two is pretty standard and sometimes both stick.
Why has it taken so long for physicians and patients in our country to accept single embryo transfer? This is America and everybody wants bigger and better. We simply won’t tolerate a lower chance of “success”. The key here is of course how you define success. “Success” is not simply a positive pregnancy test. “Success” is not a 24 week twin delivery that results in months and months of neonatal intensive care. Success should be defined as the birth of a single healthy baby.
In America we are consumers and we are inundated every day with the consumer mentality. There is no doubt that everybody wants to be successful and they want the best chance at pregnancy. But sometimes patients view themselves as a customer purchasing a product rather than as a patient coming to a physician for treatment. The biggest obstacle I face to single embryo transfer is the couple sitting across the table from me who are weighing the risk of a twin pregnancy with the potential improvement in success. Time and time again I hear patients say that they would rather have two embryos transferred because it improves success and they just can’t bear the thought of another negative pregnancy test.
In the field of reproductive endocrinology we have struggled for years to better identify which embryos are most capable of resulting in a healthy baby. In the last five years the technology of bioinformatics and molecular genetisc have been combined to develop the ability to genetically screen embryos prior to transfer. Our group at RMANJ has pioneered the use of comprehensive chromosome screening (CCS) to better identify embryos which are more likely to result in a baby. Last year we published a trial where we demonstrated that a single genetically screened embryo could result in as many healthy babies as to untested embryos. In the coming years scientists will expand our ability to screen embryos by adding metabolic markers and using time lapse imaging to better identify embryos that grow at the right pace. As science and technology expand our knowledge, the chances for success with a single embryo will increase dramatically and it should become the standard of care. For now, I am happy to be ahead of the curve, leading the way and pushing forward. My patients who have one healthy baby at a time are happy too.