A common question is whether babies conceived through In Vitro Fertilization (IVF) are more likely to be born early. Understanding the relationship between IVF and preterm birth requires a nuanced explanation, involving historical practices, maternal health, and advancements in fertility treatments.
Defining Preterm Birth and IVF
Preterm birth, also known as premature birth, occurs when a baby is born before 37 completed weeks of gestation. A full-term pregnancy typically lasts about 40 weeks. The earlier a baby is born before this 37-week mark, the higher the potential for health complications, as many organs like the brain, lungs, and liver are still developing in the final weeks of pregnancy.
In Vitro Fertilization (IVF) is a fertility treatment that assists conception by fertilizing an egg with sperm outside the body. The process involves stimulating the ovaries to produce multiple eggs, retrieving them, and then combining them with sperm in a laboratory dish. After fertilization, the resulting embryo or embryos are cultured for a few days before being transferred into the woman’s uterus.
Historical Link to Multiple Pregnancies
Historically, IVF was associated with a higher incidence of preterm birth largely due to the common practice of transferring multiple embryos into the uterus. This approach aimed to increase the chances of pregnancy success, but it frequently resulted in twin, triplet, or even higher-order multiple pregnancies.
Multiple pregnancies inherently carry a higher risk of prematurity compared to singleton pregnancies. For instance, twin pregnancies have a much greater likelihood of preterm birth, with rates substantially higher than those for singletons. This increased strain on the mother’s body and the limited space in the womb often led to earlier deliveries, contributing to the perception of IVF babies being born prematurely.
Maternal Health and IVF Procedures
Beyond multiple pregnancies, other factors contribute to the observed rates of prematurity in IVF pregnancies. Underlying maternal health conditions play a role, as women seeking IVF often have pre-existing medical issues such as advanced maternal age, hypertension, or diabetes, which independently increase the risk of preterm birth. For women aged 45 and older, IVF has been linked to a higher rate of preterm birth compared to non-IVF pregnancies in the same age group.
Aspects of the IVF procedure itself may also influence prematurity rates. Some research suggests that hormonal stimulation for egg retrieval and the type of embryo transfer, whether fresh or frozen, could have an impact.
Current IVF Trends and Preterm Birth Rates
Modern IVF practices have seen a shift towards elective single embryo transfer (eSET), where only one embryo is transferred into the uterus. This practice aims to reduce the incidence of multiple pregnancies, thereby mitigating the associated risks of prematurity. While eSET has been successful in lowering multiple birth rates, studies suggest that singleton pregnancies conceived through IVF, even with single embryo transfer, may still have a slightly increased risk of preterm birth compared to naturally conceived singletons.
Current data indicates that preterm birth rates for IVF singletons can range from approximately 8.6% to 14.9% in Europe and the United States, compared to 5.9% to 6.4% for naturally conceived singletons. This suggests that while the risk is higher, it is often attributed to underlying maternal factors or the specific reasons for infertility rather than solely the IVF procedure itself. Researchers continue to investigate the precise mechanisms behind this observed difference, including the potential role of placental development.