In vitro fertilization (IVF) is an assisted reproductive technology that helps individuals and couples achieve pregnancy by fertilizing an egg with sperm outside the body in a laboratory setting. This process involves stimulating the ovaries to produce multiple eggs, retrieving them, and then combining them with sperm. After fertilization, the resulting embryos are transferred into the uterus with the goal of establishing a successful pregnancy.
How IVF Increases Twin Chances
IVF can increase the likelihood of a twin pregnancy primarily through the deliberate transfer of more than one embryo into the uterus. Historically, fertility specialists would transfer multiple embryos to improve the overall chance of at least one embryo implanting and leading to a successful pregnancy. Each embryo transferred has the potential to implant, resulting in a multiple pregnancy. While less common, a single transferred embryo can also spontaneously split to form identical twins, a phenomenon that occurs at a slightly higher rate in IVF compared to natural conception.
Factors Influencing Twin Likelihood
The number of embryos transferred during an IVF cycle is the most significant and controllable factor influencing the probability of a twin pregnancy. Medical recommendations increasingly favor single embryo transfer (SET) to reduce the risks associated with multiple pregnancies, especially for younger patients or those with a good prognosis. Younger patients generally have higher implantation rates per embryo. High-quality embryos also have a greater chance of successful implantation. Additionally, different clinics may have varying guidelines or recommendations regarding the number of embryos to transfer, influenced by their success rates, patient demographics, and national regulations.
Types of Twins from IVF
Twins conceived through IVF can be categorized into two main types. Dizygotic, or fraternal, twins result from the implantation of two separate embryos. This is the most common type of twin pregnancy associated with IVF, largely due to the practice of transferring multiple embryos. These twins are genetically distinct, similar to any other siblings born at different times.
Monozygotic, or identical, twins develop when a single embryo splits after implantation. While less common than fraternal twins, the risk of identical twins might be slightly elevated in IVF compared to natural conception. Identical twins are genetically identical and are always of the same sex.
Considerations for Multiple Pregnancies
Carrying a multiple pregnancy carries important health considerations for both the parent and the babies. For the expectant parent, risks include gestational diabetes, preeclampsia, preterm labor, Cesarean section, and postpartum hemorrhage, necessitating more frequent medical monitoring. For the babies, there is a higher likelihood of low birth weight and prematurity, often leading to respiratory distress syndrome, extended Neonatal Intensive Care Unit (NICU) stays, and potential developmental delays.
Beyond medical aspects, raising multiples can present significant emotional and financial impacts, including increased stress and logistical challenges. It is important to discuss all potential risks and benefits of multiple embryo transfer with medical professionals. Patient safety and healthy outcomes for both the parent and the babies remain paramount in fertility treatment.