Single vs. Multiple Embryo Transfer

By: Matthew A. Lederman, MD

In vitro fertilization (IVF) has evolved dramatically over the last few decades, with more than six million babies now born through assisted reproductive technology.  For years, multiple embryos were transferred to the uterus in hopes of achieving one or more implantations.  Unfortunately, one of the consequences of this practice was multiple gestations and its associated risks.

Over the course of time, advancements and improvements in IVF culture conditions have enabled embryos to be cultured successfully to the blastocyst stage (a day 5 or 6 embryo), and therefore transferred into the uterus at the ideal time.  An advantage of extending culture to the blastocyst stage is that the embryologists can more accurately identify the best quality embryos, thereby reducing the number of embryos needed to be transferred.  As a result, a blastocyst stage transfer affords the opportunity of choosing the more viable embryo for transfer, thus optimizing the pregnancy rates while reducing the multiple pregnancy rates since fewer embryos are transferred.

This is important because a multiple pregnancy, such as a twin pregnancy, is inherently more dangerous to both the mother and the health of the developing fetus.  Risks associated with these pregnancies include preterm delivery and low birth weight, which can increase the newborn’s chance of developing respiratory distress, gastrointestinal infections and intracranial bleeding, all of which may result in longer hospital stays in the neonatal intensive care unit (NICU).  These complications unfortunately can also result in permanent and severe disability.  Maternal risks associated with a multiple pregnancy include gestational diabetes, high blood pressure, preeclampsia, increased bleeding at time of delivery and increased risk of requiring a cesarean section for delivery.  Thus, transferring fewer embryos enhances the overall safety of IVF for both the mother and the baby since these complications of a multiple pregnancy can be avoided.

Embryo screening techniques and technology have also advanced in recent years, helping to further increase the likelihood that the best single embryo is selected for transfer with the goal of achieving a healthy, singleton pregnancy.  Preimplantation Genetic Screening (PGS), or Comprehensive Chromosomal Screening (CCS), is an advanced screening technique involving biopsy of the embryo at the blastocyst stage, and analysis of the DNA to identify chromosomally normal, or euploid embryos prior to embryo transfer.  Following fertilization, embryos are now biopsied and frozen or “vitrified.”  If the biopsy reveals that the embryo is chromosomally normal, it is thawed and transferred to the uterus a few weeks later in a frozen embryo transfer cycle (FET).  Excess euploid embryos can be saved for future attempts at pregnancy, since these embryos can remain frozen indefinitely.  This embryo screening technique has increased the frequency of single embryo transfers, decreased the incidence of multiple gestations, dramatically reduced miscarriages, and has helped reduce the time to pregnancy since time lost to both failed cycles and miscarriages are minimized.  In the past several years, this technology has revolutionized reproductive medicine, and the majority of patients now conceive after transferring a single screened embryo.

A key benefit of using CCS is screening for aneuploidy, or chromosomally abnormal embryos, which are identified and then not transferred back during an IVF cycle.  This is important because aneuploidy is a significant contributing factor in implantation failure and spontaneous miscarriages, and is likely responsible for the majority of IVF failures involving the transfer of unscreened embryos.  Aneuploidy rates increase with increasing maternal age which is why older women have lower pregnancy rates and higher miscarriage rates in an IVF cycle.  Women over the age of 35 are at increased risk of having chromosomally abnormal embryos.  Guidelines have been established by the American Society for Reproductive Medicine (ASRM) for the number of unscreened embryos to transfer in IVF cycle.  In order to maximize success rates of an IVF cycle, these guidelines recommend the transfer of 2 unscreened blastocyst stage embryos in women over the age of 35.  Consequently, this places the couple at risk for a twin pregnancy, and the inherent risks and consequences associated with a multiple gestation pregnancy.  Recent studies demonstrate that transfer of a single screened embryo, has an equivalent pregnancy rate as transfer of two unscreened embryos without the risk of multiple pregnancy.

Advancements in IVF and genomics over the last few years have dramatically shifted recent focus to no longer simply assisting individuals in achieving pregnancy, but to a goal of achieving a single healthy baby.  As a result, IVF with embryo screening and transfer of a single screened embryo in an FET cycle has become the preferred method of IVF at RMA of New York.  While we work with our patients to offer the most effective treatment on an individualized basis, this approach enhances the ability to prevent a nonviable pregnancy helping patients avoid the devastating and emotional suffering from a miscarriage and is truly a more patient-oriented approach to building one’s family.


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