Those using frozen embryos had fewer pregnancy losses than those using fresh embryos (22 vs. 32.7 percent), more live births (49.3 vs. 42 percent), and the newborns had higher birth weights. There was also a reduction in the risk of ovarian hyperstimulation syndrome (OHSS), from 7.1 to 1.3 percent.
'Women with PCOS may have a higher chance of a successful pregnancy, and may have less ovarian hyperstimulation, when you electively freeze all the embryos and perform a frozen embryo transfer than if you do a fresh transfer,' said Professor Richard Legro of Penn State College of Medicine, one of the authors of the study, which was published in the New England Journal of Medicine.
'This protocol potentially offers immediate benefits to women with PCOS, so practitioners should consider freezing all embryos for these patients.'
Women with PCOS are at a higher risk of developing OHSS, a potentially life-threatening condition that can result from IVF treatment, so researchers had been looking at ways to reduce this risk. The study, led by Professor Zi-Jiang Chen of Shandong University, involved 1508 Chinese women with PCOS, who were randomly assigned to either receive fresh or frozen embryos.
The researchers suggest that allowing the ovaries and endometrium to recover after hormonal stimulation may be the reason for the improved outcomes. 'By electing to freeze all the embryos, you create a healthy environment for the best embryos, as opposed to putting them back in a disturbed environment,' explained Professor Legro.
Although there were fewer pregnancy losses in the frozen embryo group, there were two stillbirths and five neonatal deaths in this group, whereas there were none in the fresh embryo group. These differences could have been by chance. 'It's a small red flag and something that does require further investigation,' Dr Owen Davis from the Center for Reproductive Medicine at Cornell Medical College, who was not involved in the study, told the Los Angeles Times.
There was also a higher rate of pre-eclampsia in the women who received frozen embryos, although no women developed severe pre-eclampsia, which is life threatening.
In an accompanying editorial, Professor Christos Coutifaris of the University of Pennsylvania, who was not involved in the study, pointed out that using frozen embryos increases the costs of treatment by a factor of five to ten, and there is also an 'emotional cost' of deferring the embryo transfer by several weeks. But he concluded that 'in high-risk women, such as those with the PCOS, a freeze-only approach to minimise the risk of the OHSS may outweigh the costs'.