Californian researchers have reported that women over 35 can avoid multiple births by using an IVF method that transfers only a single embryo. A team led by Dr Amin Milki from Stanford University, reporting in the journal Fertility and Sterility, announced that half of the women they had studied became pregnant after undergoing the single blastocyst transfer method.
The current recommendations from the American Society for Reproductive Medicine (ASRM) advise that doctors should transfer two or more embryos into women over 35, to enhance the chances of a successful pregnancy. However, transferring more than one embryo can lead to multiple births, which carry a higher risk for both mother and fetus.
The single blastocyst transfer method involves bathing an embryo in a culture of nutrients for five days, until it reaches the blastocyst stage of development. The doctors then determine which embryos are most likely to lead to a successful pregnancy, and transfer them into the woman's uterus.
The study reviewed data from 45 patients between the ages of 35 and 43, who had decided to use the single blastocyst transfer method, at the Stanford University Medical Centre. The procedure is offered to those with good quality embryos who elect to have only one embryo transferred. In the US almost 60 per cent of IVF procedures are carried out on women over 35. The team found that 28 pregnancies were conceived, with 23 continuing beyond the first trimester. Dr Milkie said that this was 'an excellent pregnancy rate'.
Although the quality of the women's embryos meant that they had a relatively good chance of conceiving, the national success rate for IVF procedures in women aged between 35 and 43 is only 25 per cent. Dr Milkie stated that 'although these results represent a selected group of patients, we believe that they should serve as encouragement to patients and providers who are considering single blastocyst transfer in the older IVF population'.
Dr Milkie noted that the preference for one child in the group studied was not always due to health reasons, but because half of the patients already had one child and wanted just one more. However, many women are willing to risk the outcome of multiple pregnancies, because the IVF success rate is higher when multiple embryos are transferred. Dr Milkie said that the study gave reassurance that a good pregnancy rate is possible without risking multiple births. However, he conceded that for women whose embryos were of a lower quality, transferring two or three embryos might give them a better chance of pregnancy.