Single Embryo Transfer

Dr. Randy Morris

Single Embryo Transfer

Dr. Randy Morris

Single embryo transfer in in vitro fertilization - IVF may be equivalent to double embryo transfer

The chance for pregnancy in in vitro fertilization - IVF is affected by numerous factors. One important modifiable factor is the number of embryos transferred into the uterus. The data tell us that placing two embryos into the uterus will produce more pregnancies than placing one. Unfortunately, it also increases the risk of multiple pregnancy.

Multiple pregnancy, even twin pregnancy, is associated with greater risks than a singleton pregnancy. In fact, every complication that occurs in pregnancy occurs more often in twins. This includes, premature birth, gestational diabetes, hypertensive disorders of pregnancy (pre-eclampsia), birth defects and even death of the baby. The greater the number of babies in a multiple pregnancy, the greater is the risk.

Unfortunately, many in vitro fertilization - IVF programs still transfer high numbers of embryos in an attempt to boost or maintain their pregnancy rates. This may make the program look better but it puts both mother and baby in greater jeopardy.

It has been questioned, over the years, whether you can get just as many women pregnant if you put one embryo in over two different attempts compared to putting both in at once.

Recently, researcher from Sweden put that question to the test. They looked at a specific group of women undergoing in vitro fertilization - IVF. These women are generally considered to be good prognosis patients.

  • All under 35 years of age
  • On their 1st or 2nd in vitro fertilization - IVF attempt
  • Had at least two good quality embryos for transfer into the uterus

They divided these women into two groups at random. One group received transfer of two embryos. The other group had transfer of a single embryo with cryopreservation (freezing) of the remaining embryos. If not pregnant, this second group was brought back for transfer of a single frozen embryo.

The results were looked at in two ways. The pregnancy rate for each attempt or the per-cycle pregnancy rate and the cumulative pregnancy rate over two cycles.

In the double-embryo-transfer group, 142 (42.9%) of 331 women had pregnancy resulting in at least one live birth compared with a cumulative live birth rate of 29.6% after the first and 38.8% after the second transfer for the single-embryo group. It should also be pointed out that 38 women did not receive a second transfer because they did not have a viable embryo after thawing.

However, multiple births occurred in a whopping 33.1% of women in the double-embryo-transfer group and in only 0.80% of women in the single-embryo-transfer group (basically one twin pregnancy).

The difference in live birth rate between the groups was about 4% on this study. Doing some statistical analysis we can say that any reduction in the rate of live births with the transfer of single embryos is unlikely to be greater than 11.6 percentage points.

What can we conclude from all this? Well in a well selected group of good prognosis patients, transferring one embryo at a time is just about as successful as putting two embryos in at once but with a fraction of the risk for multiple pregnancies.

The costs to the patient will initially be higher because of the extra expense of embryo cryopreservation, storage, thawing and preparation of the uterus for the second transfer. However, the financial and social costs down the road will be considerably lower due to the avoidance of multiple pregnancy.

At our program, we are well known because we do very well but transfer very few embryos. We have done single embryo transfers but for the most part patients have been resistant to them. This is in part due to the fact that patients talk on the internet and in support groups and say "My doctor recommended transferring four embryos" Instead of running as fast as they can away from that program, they create the illusion that you have to transfer many embryos to get pregnant.

Another problem results from failed cycles. Patients have a tendency to demand larger and larger numbers of embryos be transferred after failed attempts even though there is no data that this will improve their chances for becoming pregnant.

We cannot continue like this for much longer. Some countries already have passed laws limiting the number of embryos that can be transferred. I don't believe we are too far from that happening here.