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How Many Embryos Should You Transfer?

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Whether or not you have had problems with fertility, most likely if you have even a vague concept of what IVF is, when you hear the phrase something in the word-association-game portion of your mind shouts 'twins!' 'triplets!' or 'octomom!'. Chances are, unless you are a reproductive endocrinologist or staring down the barrel of your first round of IVF, multiples and the Grand Poobah of fertility treatments automatically go together in your mind. And if you have gone through month after month after month after month of unsuccessful cycles, the hypothetical set of multiples can seem - rightfully so - all the more appealing.

If you're lucky enough to have everything in your in vitro cycle go as planned, you will most likely be faced with the choice of how many embryos to transfer back in.. and then your decision regarding a multiple pregnancy goes from hypothetical daydreaming to very, very real. On the one hand, there are obvious attractions to putting in more than one (my logic: I figure if the average fertile goes from deciding to have a kid to having one in 18 months I'm owed at least.... 2 1/2 kids. Not to mention the idea of being done - d-o-n-e done - after one pregnancy seems amazing). On the other hand, there are very real risks to being pregnant with multiples and for that reason many couples are electing to do single embryo transfers.

Obviously every couple going through IVF wants to feel as though they're doing everything in their power to increase their chances, while still being safe. So what are the circumstances in which a person should seriously consider doing a single embryo transfer? Who probably shouldn't? Is there a drastic difference in success rates between the two? Does your age automatically make the decision for you?

For some guidance on how to weigh this decision, I spoke to Dr. Gregory F Rosen of Reproductive Partners Medical Group in Los Angeles.

First of all, most everyone could (and maybe should) at least consider a single embryo transfer.

"All IVF patients should strongly consider having a single embryo transfer due to the safety of having one child at a time: few health issues for the mother, fewer birth defects for the child and fewer learning issues as the child grows and develops," Dr. Rosen says. "What couple don’t seem to understand is that it is a combination of their age and the quality of their embryos that determine their chance of a successful pregnancy. SART/CDC guidelines are written so that only women under the age of 35 be considered for SET but there was an article from Fertility and Sterility (2012;98:1152-6) that looked at women up to age 38 and the delivery rate for SET was 66.8%. We have done a number of successful elective SETs in women up thru age 40 What women need to take into consideration is the quality of the embryo. It is my opinion that any woman up thru age 40 should have the option of an SET if her embryos are “smoking hot.”

Apart from age or embryo quality, a woman's medical conditions should obviously come into consideration, particularly if they "might be exacerbated by multiple gestations. These include but are not limited to diabetes and hypertension," Dr. Rosen explains. "Women who have issues with their uterine cavities should also have only a single embryo transferred. These include women with anything but normal uterine cavities: bicornuate, unicornuate, didelpyic or septate uterus. Even after surgical repair, these women are still at a significant increased risk for preterm delivery so only 1 embryo should be transferred."

When making the decision of how many to have transferred, couples are most likely going to wonder how the number of embryos affects their chances of successful pregnancy. The difference in success rates between SET and the transfer of multiples may surprise you.

"It is logical that two should always be more than 1 but this may not be the case if one looks at embryo quality as the deciding factor. To follow are 2 studies which will highlight what I am saying. Gardner (Gardener et al, Fertil Steril 2004, 81:551-5) looking only at a group of women with a lot of eggs (>17) and with >6 blastocysts, showed that the pregnancy rate with a SET (61%) was less than transferring 2 embryos (76%). Those women how transferred 2 embryos had a 47% risk for delivering twins," Dr. Rosen explains. "Unfortunately, not all women are this lucky and most women do not have >6 blastocysts to choose from. A more realistic study is from von Montfoort (van Montfoort et al, Hum Reprod 2006, 21:338-42). In this study, women who had outstanding quality embryo had SETs and women with less-good embryos had two embryos transferred. In this study the pregnancy rates were identical."

That all being said - even though single embryo transfers are definitely something to heavily consider and are gaining popularity, there are patients who would still more likely benefit from the transfer of multiples given certain indicators.

"Prior failed IVF is an indication. So is age 35-40 with less than OUTSTANDING embryo quality. Women under 35 should have SETs unless there embryos are very “average” in quality," says Dr. Rosen. "This is how I practice medicine. If a woman has
beautiful quality embryos, I encourage her on her first IVF cycle to transfer only 1 embryos but if her embryos are only “good”, we tend to transfer two."

If you're faced with the decision to decide how many embryos to transfer, weigh the pros and cons, pay attention to your instincts, and listen to your Doctor.


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