BJOG Release: Selective Single Embryo Transfer Of A Blastocyst For IVF Increases Pregnancy Rate And Lowers Twin Births

The aim of any IVF treatment is for the woman to become pregnant and to give birth to a healthy baby. In order to achieve greater success, some doctors implant more than one embryo into the womb of a woman during IVF. This practice often leads to multiple pregnancy and though commonly seen as desirable by parents, multiple pregnancy carries an increased risk of preterm birth, intrauterine growth restriction, and pre-eclampsia, thereby increasing maternal, perinatal and infant mortality. There is also a greater risk of long-term poor health for surviving babies, including the risk of cerebral palsy.

In order to lower the multiple birth rate in IVF, the Human Fertilisation and Embryology Authority (HFEA), British Fertility Society (BFS) and Royal College of Obstetricians and Gynaecologists (RCOG) have all recommended single embryo transfer (SET). The catch of choosing SET for many parents has been that in the past, pregnancy rates have been lower per cycle (although they can increase the number of pregnancy attempts using embryo freezing). This is a particular problem if the number of cycles a woman can have is limited by funding.

In a new study to be published by BJOG: An International Journal of Obstetrics and Gynaecology, scientists from the Assisted Conception Unit at Guy's and Saint Thomas' Hospital in London employed selective single blastocyst transfer during IVF. The technique they have developed resulted in an increase in the clinical pregnancy rate (CPR) and a significant fall in the multiple pregnancy rate (MPR).

A blastocyst is a fertilised egg which has started to develop, ready for implantation. By waiting till the fifth day of cell division, doctors can better identify the embryos that have an improved possibility of implanting in the womb, thereby achieving higher successful pregnancy rates.

The study took place between July 2004 and July 2007 and was divided into two groups. The first group (Jul 04 - Dec 05) were offered transfer of up to three embryos into the uterus, 2 - 3 days after insemination. The clinical pregnancy rate (CPR) was 27% and the multiple pregnancy rate (MPR) was 32%. In the second group (Jan 06 - Jun 07), doctors waited until day five to allow for further development of the embryos. One high quality blastocyst was transferred. The CPR per cycle for this group was 32% and the MPR was 17%.

Using this transfer technique has the added benefit of producing surplus embryos which are suitable for cryopreservation, for parents who want to try for another baby at a later stage. This reduces the need for the woman to undergo ovarian stimulation again to retrieve her eggs for future use.

Dr Yakoub Khalaf, who led the study, said "It is a myth that single embryo transfer lowers the success rate of pregnancy. If the right patients are selected for blastocyst transfer, success rates can be maintained and multiple pregnancy can be significantly reduced.

"We believe firmly that a twin pregnancy is not an ideal outcome. People think it is two for the price of one, but the risks are real and we see the heartache time after time. I would encourage every IVF clinic to look at our results when treating their patients."

Professor Philip Steer, BJOG editor-in-chief said, "Parents who are desperate to have a baby often willingly have two embryos transferred during IVF to increase their chances of pregnancy. This has resulted in the high numbers of twin births for mothers who go through IVF, with all the major increases in pregnancy and newborn problems that multiple pregnancy brings.

"This new research has shown that the single embryo transfer of a good quality blastocyst during IVF treatment can not only increase a woman's chances of falling pregnant, but it also has the desired effect of decreasing the risk of a multiple birth.

"The promising results of this study suggest that single embryo transfer can be the way forward for many women undergoing IVF. It is important that IVF units develop the skills to ensure that only the best blastocysts are used, and at the same time, women should be better educated about the high risks of multiple pregnancy."