In Vitro Fertilization (IVF) is a widely used fertility treatment that helps many individuals and couples achieve pregnancy. As a medical procedure, IVF involves several steps outside the body to facilitate conception. A common question among those considering IVF is whether the treatment increases the likelihood of having twins or other multiple births. This concern stems from historical practices within fertility medicine.
The Connection Between IVF and Multiple Pregnancies
IVF procedures do increase the chance of conceiving twins or higher-order multiples compared to natural conception. While spontaneous twin pregnancies occur in about 1 in 80 natural conceptions, the rate is significantly higher with IVF. This increased likelihood is a direct result of how the treatment was historically designed and implemented, primarily to maximize pregnancy success.
Key Factors Increasing Twin Chances in IVF
The main reason IVF historically led to a higher rate of twins was the practice of transferring multiple embryos into the uterus. Transferring two or more embryos was common to improve the overall chance of a successful implantation and pregnancy. If more than one of these transferred embryos successfully implanted, it directly resulted in a multiple pregnancy. Ovarian stimulation, a process encouraging the ovaries to produce multiple eggs, also plays a role. Patient-specific factors, such as age, can also influence the number of embryos transferred. Younger patients often have higher quality embryos, while older patients may have more embryos transferred to compensate for lower embryo quality, increasing the chance of twins.
Minimizing the Likelihood of Twins
Medical advancements and a greater understanding of the risks associated with multiple pregnancies have led to significant changes in IVF practices aimed at reducing twin births. The most effective and widely adopted strategy is Single Embryo Transfer (SET). SET involves transferring only one embryo into the uterus during an IVF cycle, which significantly lowers the chance of multiple pregnancies while maintaining high live birth rates.
Advances in embryo selection, such as extended embryo culture to the blastocyst stage and preimplantation genetic testing (PGT), have made SET a more reliable option. These technologies allow fertility specialists to identify the most viable embryo, increasing the success rate per transferred embryo. Fertility specialists now carefully assess individual patient factors, including age, embryo quality, and previous IVF cycle outcomes, to recommend a personalized treatment plan that balances pregnancy success while avoiding multiple gestations.
Understanding Twin Pregnancies from IVF
Twin pregnancies resulting from IVF can be categorized into two main types: fraternal and identical. Fraternal, or dizygotic, twins are the most common type conceived through IVF. These occur when two separate embryos, typically transferred during the IVF procedure, both successfully implant and develop. Each fraternal twin originates from a different egg fertilized by a different sperm, meaning they are genetically distinct, similar to any other siblings.
Identical, or monozygotic, twins are less common but can also occur with IVF. This type of twinning happens when a single embryo splits into two after implantation. Certain IVF techniques, such as assisted hatching or extended embryo culture to the blastocyst stage, have been associated with a slightly increased incidence compared to natural conception.
Risks and Considerations of Multiple Pregnancies
Reducing multiple pregnancies in IVF is a significant clinical goal due to elevated health risks for both mother and babies. Mothers carrying multiples face increased risks of complications such as gestational diabetes, preeclampsia (high blood pressure during pregnancy), and a higher likelihood of preterm labor. Anemia is also more common in multiple pregnancies.
For the babies, the risks are substantial. Multiple pregnancies are associated with a higher likelihood of preterm birth, often before 37 weeks, and low birth weight. Premature babies may experience various health issues, including breathing difficulties, feeding problems, and a greater need for care in a neonatal intensive care unit (NICU). There is also an increased risk of birth defects and other complications.