Should you consider a single or double embryo transfer?
In cycles of in vitro fertilization (IVF), it is routine to stimulate the female’s ovaries to produce multiple eggs to use for fertilization. In many cases, we obtain more than one good embryo to consider for transfer to the uterus. The availability of multiple good embryos allows us to grade them and then choose the best for transfer. It also brings up a common dilemma. Should you consider a single or double embryo transfer? The answer requires us to consider several factors.
All about embryo implantation
A critical statistic in IVF is the implantation rate. The implantation rate is the proportion of transferred embryos that implant in the uterine lining. These embryos must then continue to develop until we can detect a fetal heartbeat. Implantation rate is therefore the ratio of fetal hearts to transferred embryos.
In IVF, implantation rates once were highly dependent on the age of the female who provided the eggs, as egg quality declines rapidly with age. Embryos from eggs of a 40-year-old woman had an implantation rate near 10-15%, while those from a 30-year-old had an implantation rate of 40-50%, according to national averages.
The implantation rates can increase by genetically screening the embryos before transfer. Additionally, it can help to transfer the embryos into a uterine environment that has not been subjected to ovarian stimulation, such as with frozen embryos, egg donation cycles or gestational carrier cycles. Under ideal conditions, some embryo transfers at The Fertility Center of Las Vegas can have implantation rates of 70-80% or even greater.
The greater the implantation rate, the less need to transfer multiple embryos to achieve pregnancy, creating a lower risk of a multiple pregnancy.
Is twin pregnancy really a bad thing?
Many couples facing infertility love the idea of having twins or even triplets. The birth of healthy twins is an enormous contrast against years of failure to achieve pregnancy or birth.
But twins are not always born healthy. While any pregnancy has risks, those risks are greatly increased with twin birth. Singleton deliveries have a 9% risk of low birth weight, a 2% risk of very low birth weight and a 14% risk of prematurity. These same risks increase to 57%, 9% and 65% with twin birth. With triplet birth, these risks are 96%, 34% and 97%, respectively, according to a 2006 report by the Centers of Disease Control.
Triplets are relevant to the discussion because some patients actually want three or more embryos transferred. Also, about 1% of implanting embryos will split into identical twins. As a result, even when “only” two embryos are transferred, triplet pregnancy can still occur.
The risks of low birth weight and prematurity are not to be taken lightly. These issues can lead to numerous increased risks, which in cold medical terms include prolonged hospitalization, intellectual disabilities, cerebral palsy, respiratory distress, visual issues, digestive disorders, hearing loss, jaundice, bleeding in the brain, inability to regulate body temperature, neonatal death and an increased risks in adulthood such as adult death from heart disease.
There are also increased risks to the birth mother when multiple infants are delivered. The cost of a multiple pregnancy is also greatly increased when compared to a singleton, so that the average cost of twin pregnancy is about fourfold that of a singleton, and the cost of a triplet is about tenfold that of a single.
So, should your doctor do a single or double embryo transfer?
The urge to transfer two embryos is sometimes based on the subtle fear that the embryos will somehow be wasted. Embryos not transferred can remain frozen, and frozen embryos can remain viable for 20 years or more.
The intended parents often have the freedom to choose whether to transfer one or two embryos. But they should not make this decision lightly or naively. They should make this decision only after carefully considering the risks to infants and mother, their desire for multiple children, their finances and their clinic’s implantation rate. At the Fertility Center of Las Vegas, we strongly recommend the transfer of a single embryo in all cases.