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NEW ORLEANS -- Assisted reproductive technology (ART) cycles with an embryo transfer to a gestational carrier increased the likelihood of pregnancy and live birth, an analysis of national data from 2014 to 2020 showed.

In over 1 million ART cycles with an embryo transfer, those with a gestational carrier were more likely to result in pregnancy, clinical pregnancy, and live birth compared with those without a gestational carrier, reported Lisa M. Shandley MD, MSc, of the Emory Reproductive Center in Atlanta, during the American Society for Reproductive Medicine annual meeting:

• Pregnancy: 73% vs 63.4% (adjusted relative risk [RR] 1.06, 95% CI 1.06-1.07)
• Clinical pregnancy: 63.7% vs 52.9% (aRR 1.09, 95% CI 1.08-1.10)
• Live birth: 54.3% vs 43.6% (aRR 1.11, 95% CI 1.10-1.12)

The study findings were simultaneously published in a research letter in .

During her presentation, Shandley defined a gestational carrier as "a person who carries a pregnancy on behalf of intended parents following implantation of an embryo that was created using gametes that originated from the intended parents or a third party."

All but three U.S. states reported at least one embryo transfer to a carrier, and more than a third of gestational carrier cycles occurred in California.

"Despite several states having laws that deemed surrogacy illegal during the course of the study, many of them still reported embryo transfers to GCs [gestational carriers]," Shandley said.

Over the study period, use of embryo transfers increased, with an exception for 2020, which Shandley noted reflects the impact of COVID pandemic shutdowns on non-emergency medical care, such as ART procedures.

In 2014, the percentage of gestational carrier cycles was 2.7%, which grew to 5.2% in 2019, then decreased in 2020 to 4.6% (P<0.001 for overall trend).

ART cycles that used a gestational carrier were more likely to have older and nulligravid intended parents, use donor oocytes, have a younger age for oocyte donor or intended parent at time of retrieval, and use pre-implantation genetic testing compared with cycles that did not use a carrier. Two or more embryos were transferred in 27.6% of cycles with a gestational carrier and 36.0% of cycles without a gestational carrier.

After adjusting for pregnancy plurality, cycles that used a gestational carrier versus those that did not also had lower risks of preterm birth (23.2% vs 23.7%, respectively; aRR 0.80, 95% CI 0.78-0.82) and very preterm birth (3.6% vs 3.6%; aRR 0.76, 95% CI 0.70-0.83).

There were also higher rates of twins among cycles with gestational carriers. For live births, 14.8% of carrier cycles resulted in twins or higher multiples compared with 12.6% of those without carriers (aRR 1.15 95% CI 1.11-1.18). In cases of multiple births, most of both types of cycles involved transferring two or more embryos (90% for carrier cycles and 91.5% for non-carrier cycles).

Regarding the increased rate of twins, Rachel Weinerman, MD, of Case Western Reserve University in Cleveland, told MedPage Today, "I would say, from my perspective as a clinician, it should be the opposite. You know, I really don't want to transfer more than one embryo to a gestational carrier. Because she's already taking on substantial risks, getting pregnant with somebody else's embryo. I would want to minimize those risks in every way possible, and we know the best way to improve pregnancy outcomes following IVF is to transfer one embryo at a time."

She also noted that the finding of increased utilization of pre-implantation genetic testing was noteworthy. "Many people choose to do pre-implantation genetic testing so they can try to avoid having chromosomal abnormalities that require termination, or to have miscarriages due to chromosomal issues."

Both Shandley and Weinerman pointed to the increasing use of gestational carriers as being tied to more access and usage by LGBTQ patients and changing surrogacy laws.

"There are so many new options for family building, Weinerman said. "And there's definitely an increased utilization of reproductive services by LGBTQ+ couples, especially if you have a couple in which neither has a uterus, their only option for conception is going to be gestational carrier."

For this study, Shandley and colleagues analyzed de-identified data from the Society for Assisted Reproductive Technology Clinic Outcomes Reporting System involving an embryo transfer between 2014 and 2020. They included 1,008,205 ART cycles with an embryo transfer, 4% of which utilized a gestational carrier.

The research was limited by the inability to investigate pregnancy complications or clustering by gestational carrier. Data entry errors were also possible.

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