Frozen Embryo Transfers Increase Pregnancy Rates in Women Age 35+

by: Dr. Sung Tae Kim, PhD., Head Embryologist at Carolina Conceptions


Carolina Conceptions recently completed a retrospective study to compare the pregnancy rates of fresh vs. frozen embryo transfers in women 35 years and older. The results were presented at the 2017 CRB (College of Reproductive Biology) Symposium.  279 embryo transfer cycles were analyzed at Carolina Conceptions. 172 of them were fresh embryo transfers and 107 were frozen embryo transfers. Egg donor, gestational carriers, and patients who completed embryonic testing (PGS/PGD), were excluded. Embryos of the best quality were selected for both fresh and frozen transfers completed. Based on the data obtained from this study, the team of physicians and embryologists at Carolina Conceptions have concluded frozen embryo transfers are MORE EFFECTIVE in women 35 years and older at reducing early pregnancy loss and improving the chances for continuing pregnancies than fresh embryo transfers.


Here Are Some Definitions to Help You Interpret the Data:

-Biochemical pregnancy is a positive hCG blood test confirming pregnancy. When a visual confirmation of pregnancy is attempted via ultrasound, there is no gestational sac present, or the sac has not developed properly, indicating early pregnancy loss. Findings in this study conclude the biochemical pregnancy rate (21-24%) is much higher in women ages 35+ who had a fresh embryo transfer than those who opted for a frozen embryo transfer (4-7%!).

-Clinical pregnancy is a positive hCG blood test confirming pregnancy as well as a visual confirmation of pregnancy via ultrasound.  The visual confirmation of an age appropriate and properly developed gestational sac encourages hope for a continued pregnancy, and later, live birth. In this study the rates are MUCH higher (56-57%) from those who had a frozen transfer vs. the women who had fresh transfers (33-40%).

-Implantation rate is the number of  confirmed beating hearts from clinical pregnancies seen via ultrasound out of the number of embryo(s) transferred. For example, if two embryos were transferred and one beating heart was shown, the implantation rate would be 50%. In this particular study, Carolina Conceptions found women who completed a frozen embryo transfer were found to have pregnancies with a fetal heart beat at a rate of 35-41% vs. those who elected for a fresh transfer, with heart beats visible in only 18-24% of cases monitored.


Data: Pregnancy Rate By Age Group

≥ 35 yrs ≥ 38 yrs
Fresh (n=172) FET (n=107) Fresh (n=89) FET (n=39)
Age 37.98±2.49 37.38±2.3 39.92±1.84 39.79±1.77
Number of embryos transferred 2.06±0.7 1.66±0.49* 2.19±0.83 1.58±0.55*
Pregnancy rate per transfer 52.9% 62.6% 42.7% 59.0%*
Clinical pregnancy rate per transfer 40.1% 57.9%* 33.7% 56.4%*
Implantation rate 24.9% 41.0%* 18.5% 35.5%*
Biochemical pregnancy rate 24.2% 7.5%* 21.1% 4.3%*

*The result is significant at p<0.05.


Ultimately, What Does This Mean? 

The data found in this study suggests frozen embryo transfers increase pregnancy rates in women age 35 years and older. The findings also support a hypothesis that ovarian hyperstimulation (which can occur in a fresh cycle), might affect endometrial (uterine) receptivity in some patients of this age group. For this reason, it is believed frozen transfers will yield more positive outcomes for women ages 35+ who are undergoing in vitro fertilization.