Frozen-embryo transfer resulted in significantly lower rates of ovarian hyperstimulation syndrome compared to fresh-embryo transfer.
But whether frozen embryos contributed to the same pregnancy and live birth rates as fresh embryos wasn't clear.
The study included nearly 800 couples undertaking IVF in Vietnam, who received either fresh or frozen embryo transfers on a randomised basis and was completed in under a year.
Previous trials have suggested that using only frozen embryos might improve pregnancy rates in women with polycystic ovary syndrome, or PCOS, a hormonal disorder that affects about 10 percent of women.
Women experiencing infertility but want to have children may have more options than previously thought when it comes to in-vitro fertilization, two large studies show. Using block randomization, they assigned the women to either fresh-embryo transfer or embryo cryopreservation followed by frozen-embryo transfer.
The study, published in The New England Journal of Medicine, investigated nearly 800 women who had infertility not related to polycystic ovarian syndrome (PCOS). A new study now gives couples trying IVF peace of mind whichever method they choose, showing both fresh and frozen embryo transfers offer an equal chance of having a child.
"This new study shows that infertile women not suffering from PCOS have equivalent live IVF birth rates from frozen embryos, which is important news for infertile women worldwide", said the scientist.
But until now, it was not known whether this was also the case for women confronted with fertility problems due to other reasons. Each woman received up to two cleavage-stage embryos.
The rates of the syndrome in the Chinese study were 0.6 percent with frozen embryos and 2.0 percent with fresh. The improvement came primarily from a lower rate of pregnancy loss.
"Given the differences in the uterine condition and embryo characteristics between cleavage-stage embryo transfer and blastocyst transfer, our results may not be applicable to cycles with blastocyst transfer", they wrote.
In the second, of 782 women without PCOS, live birthrates were 33.8 percent for the frozen-embryo group and 31.5 percent for the fresh, again an insignificant difference.
Neither study found a higher risk of neonatal or obstetrical complications in either group, although frozen embryo transfer produced a statistically lower risk of over-stimulated ovaries, which leads to swollen and painful ovaries and is potentially risky.
In a 12-month post-hoc analysis, the median time to pregnancy was slightly higher in the frozen-embryo group compared with the fresh-embryo group (3.6 months versus 2.2 months), but the cumulative ongoing pregnancy rate 1 year after randomization was similar (54.2% versus 53.5%).
The study was funded by the National Key Research and Development Program of China and the National Natural Science Foundation of China.
The study by Vuong et al was supported by My Duc Hospital in Ho Chi Minh City, Vietnam.