Impact of Frozen Embryos on Live Birth Rates in IVF

Introduction to In Vitro Fertilization

In vitro fertilization (IVF) is a medical procedure that involves combining sperm and egg outside the body for subsequent implantation into a woman’s uterus. Over the past 40 years, advancements in IVF have improved success rates, including enhanced egg retrieval through controlled hormonal stimulation and the ability to preserve embryos for future use. Recent studies suggest that using frozen embryos might create a more favorable environment for implantation, particularly in women with regular ovulatory cycles.

Study on Frozen vs. Fresh Embryos

A recent study published in the New England Journal of Medicine by researchers in China sought to determine whether the implantation of fresh or frozen embryos leads to similar birth rates in women with regular ovulatory cycles. The primary outcome measured was live birth after the first embryo transfer, with maternal and neonatal complications also assessed.

Methodology of the Study

The study utilized a randomized controlled trial design, enrolling 2,157 couples where both partners were involved. Participants were assigned in a 1:1 ratio to either the frozen or fresh embryo group. Women aged 20-35 with regular menstrual cycles were included if they were undergoing their first cycle of IVF or intracytoplasmic sperm injection due to factors related to their fallopian tubes or male partner infertility.

Participants were excluded if they had preexisting medical conditions that could adversely affect pregnancy outcomes, such as hypertension, diabetes, or liver dysfunction. Additionally, those with uterine pathologies like submucosal fibroids, adenomyosis, or polycystic ovary syndrome were not included.

IVF Protocol for Participants

All participants underwent ovarian stimulation using gonadotropin-releasing hormone (GnRH) starting on day three of their menstrual cycle. Women in the fresh embryo group received additional daily support with vaginal progesterone gel and oral dydrogesterone. Up to two embryos were selected for transfer based on their development. For those receiving frozen embryos, up to two thawed embryos were transferred post-ovulation, with clinical pregnancy confirmed via transvaginal ultrasound three weeks later.

Findings on Birth Rates and Complications

The results indicated no significant difference in live birth rates between the fresh embryo group (50.2%) and the frozen embryo group (48.7%). However, further analysis revealed a lower rate of second-trimester pregnancy loss in the frozen embryo group (1.5%) compared to the fresh embryo group (4.7%). Additionally, women who received frozen embryos experienced a reduced incidence of moderate to severe ovarian hyperstimulation syndrome, a potentially serious condition associated with fertility treatments.

Limitations of the Study

The study faced certain limitations, including a withdrawal rate exceeding 15% and the absence of blinding, which could introduce bias into the findings.

Conclusion of the Study

The study concluded that while there was no overall difference in live birth rates between the frozen and fresh embryo groups, the use of frozen embryos was associated with a lower risk of ovarian hyperstimulation syndrome.

Author Information

Written by Kimberly Spencer B.Sc. (Hons).

Reference

Shi, Y., Sun, Y., Hao, C., Zhang, H., Wei, D., & Zhang, Y. et al. (2018). Transfer of Fresh versus Frozen Embryos in Ovulatory Women. New England Journal Of Medicine, 378(2), 126-136. http://dx.doi.org/10.1056/nejmoa1705334