As with all things, the prevailing wisdom about embryos claims fresh is better than frozen. However, a new study has overturned that belief, finding that in women with PCOS, frozen embryos have better success rates than fresh embryos.
The study comes from Richard Legro, Professor of Obstetrics, Gynecology and Public Health Sciences at Penn State College of Medicine, along with other researchers from Pennsylvania and China. The researchers published their results August 11th in the New England Journal of Medicine. Although fresh is usually better, some research had suggested frozen embryos might actually reduce pregnancy complications in women with polycystic ovary syndrome (PCOS). The researchers in the current study set out to see if frozen embryos really are better for women with PCOS.
The researchers recruited 1,508 women for their study across several reproductive medicine centers in China. These women all had PCOS which resulted in infertility, so they needed in vitro fertilization (IVF) to become pregnant. In IVF, medical staff use drugs or hormones to induce ovulation then remove those mature eggs from the patient. They then fertilize the eggs with sperm, allow the cells to divide, and either implant an embryo into the patient’s womb or freeze the embryos for future use. In the current study, half of the women were randomly assigned to receive fresh embryos and half of the women were randomly assigned to receive frozen embryos.
When women with PCOS become pregnant using IVF, their pregnancy troubles are not over yet. These women have an increased risk of ovarian hyperstimulation syndrome, a potentially-fatal complication that can require drugs, hospitalization, and possibly surgery. They also face a higher risk of other complications like miscarriage, high blood pressure called preeclampsia, delivering their baby prematurely, and having a baby with low birth weight and birth defects. Because of this, even when women with PCOS undergo IVF, they may not have a successful pregnancy.
The researchers looked at the rate of live births and complications in women with PCOS who received fresh embryos compared to women with PCOS who received frozen embryos. It turns out that while women with fresh embryos had ovarian hyperstimulation syndrome 7.1 percent of the time, the women with frozen embryos only had that complication 1.3 percent of the time. The women with frozen embryos also had fewer pregnancy losses, and therefore more live births, than their counterparts with fresh embryos. Not only that, the babies that began as frozen embryos tended to have higher birth weights. It seems that women with PCOS who receive frozen embryos have fewer complications and a higher chance of a successful pregnancy than those who receive fresh embryos.
There were two negatives of the frozen embryo transfer versus the fresh embryo transfer, the researchers discovered. Women with frozen embryos were more likely to experience preeclampsia, although no patients in the study developed severe preeclampsia which might put their and the baby’s health at risk. The frozen embryos were also more likely to experience death within a month after birth, although the difference was not significantly different. The study authors urge further study to examine these two negative outcomes.
Overall, though, the frozen embryos resulted in greater pregnancy success. The study authors believe this difference in success rate has to do with timing. During IVF treatments, doctors usually prescribe drugs and hormones to women to stimulate their ovaries to release multiple eggs. The medical staff then have more eggs to choose from when deciding which to fertilize, giving them a better chance of choosing the best one. As much as these drugs and hormones help IVF treatments, though, they can create a potentially-harmful environment for the embryo. When a fresh embryo is placed in the womb, the drugs and hormones may make it difficult for the embryo to implant and thrive. However, when the embryo is frozen and implanted later, it gives time for the fertility drugs to clear from the woman’s system and for her endometrial lining to shed, producing a fresh and nurturing environment for the embryo.
The researchers suggest that fertility doctors take note of their findings. If they freeze embryos and allow the woman’s body to recover after using drugs and hormones to stimulate her ovaries, they can help increase the chances of a live birth.
PCOS, polycystic ovary syndrome, is a hormonal disorder that affects ten percent of women in their childbearing years. The woman develops growths in her ovaries and her hormones get out of balance, leading to more male hormones called androgens and insulin resistance, which is when the body has problems using insulin to control blood sugar. These changes can lead to problems menstruating and ovulating, acne problems, extra facial and body hair, weight gain, and later on, an increased chance of developing diabetes. Because of the menstruation and ovulation problems, women with PCOS may have trouble becoming pregnant, turning to medical interventions like IVF treatments for help.