Introduction

With the increasing use of assisted reproductive technology (ART), the number of cryopreserved embryos in storage has increased, as residual viable embryos from an in vitro fertilization (IVF) cycle may be frozen for future use. Each embryo maintains attributes reflective of the age of the female at time of the original oocyte retrieval. Embryo donation, a form of third-party reproduction, involves donation without compensation of previously formed embryos to another couple for implantation. The American Society for Reproductive Medicine Ethics Committee suggests that the donation of embryos to a recipient couple to “support family-building efforts of others is an important option for patients considering the disposition of cryopreserved embryos in excess of those needed to meet the patients’ own fertility goals.” Use of donated embryos may be particularly appealing to a couple with both male and female factors contributing to their infertility, to an individual who requires both an oocyte and sperm donor, and to patients who are drawn to the relative affordability of a donor embryo cycle as compared to either an autologous or donor oocyte cycle.

Currently, limited published data exist detailing outcomes of donor embryo cycles. Two prior studies published in 2000 through 2003 surveyed ART clinics to determine the proportion of clinics that performed donor embryo transfers and the percentage of embryos potentially available to donate to another couple. Previously published outcome data from the United States only include data through 2008 and a small number of clinics and embryo donation agencies. The most comprehensive study published in 2012 includes cycles from 2001 through 2008 in several European countries and the United States and reports a live birth rate per transfer ranging from 14-33%; the US contribution (2001 through 2007) included 4595 donor embryo transfers that resulted in 1510 (33%) live births. To our knowledge, no published national outcomes data reflective of current practice exist for donor embryo transfers performed in the United States since 2007; such information would be helpful in patient counselling.

We aimed to describe national donor embryo trends from 2000 through 2013 and recipient characteristics and donor embryo outcomes from 2007 through 2013 in the United States.

Materials and Methods

The National ART Surveillance System (NASS), a federally mandated reporting system that captured >95% of ART cycles performed in the United States from 2000 through 2013, was used to study trends and outcomes of donated embryo transfers. Donor embryo cycles are cycles involving “embryos derived from oocytes previously fertilized for another couple’s ART therapy that were subsequently donated.” We restricted our analysis to frozen cycles as embryos are typically donated after they have been cryopreserved; 6773 of the 6838 or 99% of the reported donor embryo cycles were frozen cycles. NASS contains cycle-level data including patient demographics, medical and obstetric history, infertility diagnoses, detailed parameters of each ART treatment cycle and, if applicable, the resultant pregnancy outcome. Limited data regarding donated embryos’ origins are collected in NASS. No data are collected regarding the genetic patients’ reason for using ART, the outcome of the original ART cycle (whether it resulted in pregnancy or not), or the embryos’ stages (cleavage or blastocyst) at cryopreservation or subsequent transfer. Age of the oocyte source at the time of the donated embryo’s creation was added to NASS in 2007.

Trends in the absolute number of frozen donor embryo transfers, percentage of frozen donor embryo transfers among all ART frozen transfers, average recipient age, and overall pregnancy and live birth rates per frozen donor embryo transfer are reported from 2000 through 2013. We calculated the trend in the average age of the donor embryo oocyte source, equivalent to oocyte age at time of retrieval, from 2007 through 2013 (the years for which oocyte age was available); however, these results should be interpreted with caution as 65.3% of the donor cycles performed during this period were missing oocyte age information. Linear regression was used to explore trends in the number of cycles and average ages and binomial regression with an identity link was used to explore trends in the proportion of cycles from 2000 through 2013. We tested for quadratic and linear trends, and used generalized estimating equations to adjust for clustering by clinic.

We then investigated characteristics and outcomes of donor embryo transfers performed during 2007 through 2013. We used more recent years since the age of the oocyte donor source was collected in NASS during this period and the results would be more relevant to current practice and patient counselling. We reported the number and percentage of clinics in each geographic region of the United States performing donor embryo transfers. Next, we detailed recipient and cycle characteristics of donor embryo transfer cycles. Finally, we explored outcomes, reporting the number and percentage of frozen donor embryo transfers resulting in intrauterine pregnancy and live birth (the birth of at least 1 live born infant at ≥20 weeks); the number and percentage of pregnancies after frozen donor embryo transfer resulting in miscarriage (complete loss of the pregnancy at <20 weeks); and the number and percentage of live births after frozen donor embryo transfer resulting in singletons, twins, and full-term and normal birthweight (≥37 weeks and ≥2500 g). Among those cycles for which oocyte donor age was available (n = 2347), we calculated pregnancy and live birth rate per transfer and miscarriage rate per cycles among cycles for which the oocyte donor was <35, 35-37, and ≥38 years at time of oocyte retrieval.

This study was approved by the Institutional Review Board of the Centers for Disease Control and Prevention. All statistical tests were 2-sided and statistical significance was determined using an alpha level of 0.05. All analyses were conducted using software (SAS, v. 9.3; SAS Institute Inc, Cary, NC).

Materials and Methods

The National ART Surveillance System (NASS), a federally mandated reporting system that captured >95% of ART cycles performed in the United States from 2000 through 2013, was used to study trends and outcomes of donated embryo transfers. Donor embryo cycles are cycles involving “embryos derived from oocytes previously fertilized for another couple’s ART therapy that were subsequently donated.” We restricted our analysis to frozen cycles as embryos are typically donated after they have been cryopreserved; 6773 of the 6838 or 99% of the reported donor embryo cycles were frozen cycles. NASS contains cycle-level data including patient demographics, medical and obstetric history, infertility diagnoses, detailed parameters of each ART treatment cycle and, if applicable, the resultant pregnancy outcome. Limited data regarding donated embryos’ origins are collected in NASS. No data are collected regarding the genetic patients’ reason for using ART, the outcome of the original ART cycle (whether it resulted in pregnancy or not), or the embryos’ stages (cleavage or blastocyst) at cryopreservation or subsequent transfer. Age of the oocyte source at the time of the donated embryo’s creation was added to NASS in 2007.

Trends in the absolute number of frozen donor embryo transfers, percentage of frozen donor embryo transfers among all ART frozen transfers, average recipient age, and overall pregnancy and live birth rates per frozen donor embryo transfer are reported from 2000 through 2013. We calculated the trend in the average age of the donor embryo oocyte source, equivalent to oocyte age at time of retrieval, from 2007 through 2013 (the years for which oocyte age was available); however, these results should be interpreted with caution as 65.3% of the donor cycles performed during this period were missing oocyte age information. Linear regression was used to explore trends in the number of cycles and average ages and binomial regression with an identity link was used to explore trends in the proportion of cycles from 2000 through 2013. We tested for quadratic and linear trends, and used generalized estimating equations to adjust for clustering by clinic.

We then investigated characteristics and outcomes of donor embryo transfers performed during 2007 through 2013. We used more recent years since the age of the oocyte donor source was collected in NASS during this period and the results would be more relevant to current practice and patient counselling. We reported the number and percentage of clinics in each geographic region of the United States performing donor embryo transfers. Next, we detailed recipient and cycle characteristics of donor embryo transfer cycles. Finally, we explored outcomes, reporting the number and percentage of frozen donor embryo transfers resulting in intrauterine pregnancy and live birth (the birth of at least 1 live born infant at ≥20 weeks); the number and percentage of pregnancies after frozen donor embryo transfer resulting in miscarriage (complete loss of the pregnancy at <20 weeks); and the number and percentage of live births after frozen donor embryo transfer resulting in singletons, twins, and full-term and normal birthweight (≥37 weeks and ≥2500 g). Among those cycles for which oocyte donor age was available (n = 2347), we calculated pregnancy and live birth rate per transfer and miscarriage rate per cycles among cycles for which the oocyte donor was <35, 35-37, and ≥38 years at time of oocyte retrieval.

This study was approved by the Institutional Review Board of the Centers for Disease Control and Prevention. All statistical tests were 2-sided and statistical significance was determined using an alpha level of 0.05. All analyses were conducted using software (SAS, v. 9.3; SAS Institute Inc, Cary, NC).