In a group of infertile women with normal ovulation, rates of live birth were almost 49 percent in those who received frozen embryos.
This discovery means that doctors treating patients who don't have PCOS may now implant one embryo at a time instead of multiple embryos at once, which can often lead to multiple births. Prior studies of women with PCOS have suggested that frozen embryo transfer is more successful.
"Now these two papers, equally large and done in non-PCOS patients, show that in terms of live birth, which is what we care about, there is no difference", he told Reuters Health by phone.
In the Chinese study of 2,157 women undergoing their first in-vitro fertilization cycle, the birth rate was 48.7 percent with thawed embryos and 50.2 percent with fresh. "So to apply the rule to everybody that we should freeze your embryos is probably not correct".
Using frozen embryos for in-vitro fertilization (IVF) is as effective as using fresh embryos, an Australian study has found. "This is one of the reasons why our research is important for fertility clinicians and researchers, and of course couples who are hoping to have a child", said Lan N. Vuong from the University of Medicine and Pharmacy in Vietnam.
After the first completed cycle of IVF, ongoing pregnancy occurred in 36% of women in the frozen embryo group, and in 35% of the fresh embryo group.
Vuong and her colleagues also discovered that women with high levels of progesterone might be better off getting implanted with a thawed frozen embryo.
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Freezing embryos also allows couples to take advantage of genetic testing, which can pick up potentially lethal genetic diseases and guide doctors in deciding which embryos to implant. The corresponding figures for live birth rates were 32% and 34%.
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 unsafe.
While there was no significant difference between groups in rates of biochemical pregnancy, clinical pregnancy, implantation, ongoing pregnancy, and overall pregnancy loss, a post-hoc analysis showed that the rate of second-trimester pregnancy loss was lower in the frozen-embryo group than in the fresh-embryo group (1.5% versus 4.7%; RR 0.33, 95% CI 0.16-0.68, P=0.002). The senior author was Dr. Zi-Jiang Chen of Shandong University, who did not respond to emailed questions.
The study included more than 2,100 women undergoing their first round of IVF.
"Further research will be needed to compare pregnancy outcomes and live birth rates from other embryo freezing techniques", he said.
"It's not an easy process to go through... the probability of falling pregnant was quite low back then through IVF, for me certainly", Monroe, 51, said. "And that's reassuring for people who do a lot of frozen embryo transfer, which most of us are doing".