In Vitro Fertilization (IVF) is an assisted reproductive technology where an egg is fertilized with sperm in a laboratory setting, and the resulting embryo(s) are transferred into the uterus. While IVF helps many achieve pregnancy, it can notably increase the likelihood of conceiving twins or other multiple births compared to natural conception.
How IVF Affects Multiple Birth Likelihood
IVF procedures increase the chance of multiple births primarily because fertility specialists often transfer more than one embryo into the uterus. This strategy aims to enhance the chances of at least one successfully implanting, but inherently raises the possibility of more than one embryo implanting.
Most twins conceived through IVF are fraternal (dizygotic), developing from two separate embryos that were both transferred and implanted. Identical (monozygotic) twins are less common but can occur if a single transferred embryo spontaneously splits into two. This splitting is a random event, though its rate might be slightly higher in IVF pregnancies compared to natural conceptions.
Key Factors Influencing Multiple Births
The number of embryos transferred during an IVF cycle is the most significant factor. Transferring two or more embryos directly increases the chances of twins or triplets. Many fertility clinics now prioritize single embryo transfer (SET) to minimize these risks.
Maternal age also plays a role. Younger patients, particularly those under 35, generally have higher implantation rates per embryo, which can increase the chance of multiples if more than one embryo is transferred. The quality of the embryos selected for transfer is another important variable, as higher-quality embryos are more likely to implant. The use of fertility medications to stimulate the ovaries can also lead to the production of multiple eggs, influencing the number of embryos available for transfer.
Health Considerations for Multiple Pregnancies
Carrying multiple babies introduces increased health risks for both the pregnant individual and the infants. For the mother, these risks include a higher incidence of gestational diabetes and preeclampsia. Multiple pregnancies are also associated with an increased likelihood of needing a Cesarean section for delivery.
Preterm birth, defined as birth before 37 weeks of gestation, is a substantial concern, with approximately 60% of twins being born prematurely. Babies born early are at a higher risk of low birth weight, respiratory distress syndrome, and developmental delays.
Approaches to Manage Multiple Birth Chances
To mitigate the risks associated with multiple pregnancies, medical professionals recommend strategies like Elective Single Embryo Transfer (eSET). eSET is the most effective method for reducing multiple birth rates in IVF, as only one embryo is chosen for transfer, even when multiple healthy embryos are available.
Embryo quality assessment and preimplantation genetic testing for aneuploidy (PGT-A) can support eSET. PGT-A screens embryos for chromosomal abnormalities, helping identify the most viable embryo for transfer and improving success rates with a single embryo. Discussions with fertility specialists are essential to weigh the desire for twins against the health implications, ensuring an informed decision.