Single Embryo Transfer and Preimplantation Genetic Testing
There are several steps required for in vitro fertilization (IVF): Ovulation induction, egg retrieval, insemination and fertilization, and embryo transfer. In this blog we will take a detailed look at the embryo transfer stage. At this stage of the process a woman’s eggs have already been retrieved, inseminated, and grown to the blastocyst stage of development.
Preimplantation Genetic Testing
Before the embryo(s) are transferred to a woman’s uterus, preimplantation genetic testing (PGT) may be performed to ensure that embryos of the highest quality are being transferred. PGT is comprised of two distinct parts: Preimplantation Genetic Diagnosis (PGD) and Preimplantation Genetic Screening (PGS).
Preimplantation Genetic Diagnosis (PGD)
Preimplantation Genetic Diagnosis (PGD) is used to diagnose embryos that may be affected with inherited single gene disorders such as cystic fibrosis or sickle cell disease. PGD is also used to evaluate embryos at risk for sex linked disorders such as hemophilia or an unbalanced translocation (extra or missing genetic information).
Preimplantation Genetic Screening (PGS)
Preimplantation Genetic Screening (PGS) is an option for patients who would like their embryos screened for the correct number of 46 chromosomes or who desire sex selection for family balancing. In addition, women with multiple prior miscarriages, unsuccessful IVF cycles, or advanced maternal age may benefit from PGS. SelectCCS is a specific brand of PGS. SelectCCS is the most validated and proven method of comprehensive chromosome screening available. With greater than 98% accuracy in aneuploidy screening, SelectCSS has been extensively evaluated in more than 20 peer-reviewed research publications.
Single Embryo Transfer
The last 30 years have seen a dramatic increase in the incidence of twin and triplet pregnancies in the United States. Fertility doctors have been largely responsible. 1 in every 30 infants born in 2009 were twins; double that of 30 years ago. The serious risks of triplet pregnancies are generally well understood. Most people, however, believe that twins do great. Surprisingly, 25% of twins require neonatal intensive care hospitalization, and the risk of cerebral palsy and even death are higher for twins compared to a single baby.
Elective single-embryo transfer (eSET) is a procedure (with the help of SelectCCS) in which a single, high quality embryo is selected and transferred into the uterus. It is recommended that eSET is used for patients ages 35 or older, or who have had multiple unsuccessful IVF cycles or miscarriages. Approximately 60% of early miscarriages are due to chromosomal abnormalities in the embryo.
Update (July 2014): To further shine light on this important discussion, the NY Times ran a feature on single embryo transfer entitled “Fertility Clinics Scan for the Strongest Embryo.”
The chromosomal testing is called preimplantation genetic screening, or P.G.S. This is different from a related technique called preimplantation genetic diagnosis, which tests embryos for specific mutations with the goal of preventing the birth of a baby with a genetic disease. With the chromosomal screening, the goal is mainly to improve birthrates, not influence the traits of the baby.
Update (October 2016): The NY Times tackles the subject of Elective Single Embryo Transfer once again in their feature entitled “Some I.V.F. Experts Discourage Multiple Births.”
In recent years, professional organizations concerned about the safety of multiple gestations and births for both mothers and their babies have been recommending that only one, and at most two, healthy embryos be transferred at a time. The benefit of this advice is already apparent: The rate of I.V.F. pregnancies that resulted in multiple births dropped to 22 percent in 2014 from 50 percent in 2009.