Intracytoplasmic Sperm Injection (ICSI) is a specialized fertility treatment often used with in vitro fertilization (IVF). This article clarifies the relationship between ICSI and multiple births, detailing the factors that influence the chance of conceiving multiples during fertility treatments.
Understanding ICSI
ICSI is an advanced form of IVF where a single sperm is injected directly into an egg to achieve fertilization. This differs from conventional IVF, where many sperm are placed near an egg, allowing natural fertilization. The procedure is recommended for couples with male factor infertility, such as low sperm count or poor sperm motility. It is also used for previous fertilization failure during standard IVF cycles.
ICSI aims to overcome specific fertilization barriers, improving the chance of a successful embryo formation. The process involves ovarian stimulation to produce multiple eggs, followed by egg retrieval. After sperm injection, the fertilized egg, now an embryo, is cultured in the laboratory before transfer into the uterus.
ICSI and Twin Pregnancies: The Direct Connection
ICSI, the injection of a single sperm into an egg, does not inherently cause a higher rate of fraternal twins. Fraternal twins result from the fertilization of two separate eggs, primarily influenced by the number of embryos transferred, not the fertilization method. Research indicates ICSI does not promote embryo splitting, which leads to identical twins, more than other assisted reproductive technologies.
However, the overall process of assisted reproductive technology (ART), including ICSI, is associated with a higher incidence of identical (monozygotic) twinning compared to natural conception. While the natural rate of monozygotic twinning is about 0.42%, it can range from 1.2% to 8.9% with ART. This slightly increased rate is linked to factors like extended embryo culture or manipulations during the procedure, rather than the sperm injection itself.
Factors Influencing Multiple Births in Fertility Treatment
The most significant factor contributing to multiple pregnancies in fertility treatments is the number of embryos transferred into the uterus. When more than one embryo is placed, each has the potential to implant, increasing the likelihood of twins or higher-order multiples. For instance, transferring two embryos significantly raises the chance of fraternal twins.
Patient age also plays a role; younger patients generally have higher implantation rates per embryo, increasing their chance of multiples if multiple embryos are transferred. Ovarian response to fertility medications can also indirectly influence the potential for multiples. These medications stimulate the ovaries to produce multiple eggs, which are then collected for fertilization. While this increases the number of embryos available, the decision to transfer multiple embryos remains the primary driver of multiple gestations.
Risks and Management of Multiple Pregnancies
Multiple pregnancies carry increased health considerations for both the birthing parent and the babies. For the parent, risks include gestational hypertension, preeclampsia, gestational diabetes, and preterm labor. There is also an elevated risk of anemia and postpartum hemorrhage.
Babies born from multiple pregnancies face higher risks of prematurity and low birth weight, often requiring neonatal intensive care (NICU). They also have about twice the risk of certain birth anomalies, such as neural tube defects or heart issues.
To mitigate these risks, fertility clinics increasingly recommend elective single embryo transfer (eSET), especially for patients with a good prognosis. This involves transferring only one high-quality embryo, which significantly reduces the chance of multiple births without substantially lowering overall pregnancy success rates. This approach prioritizes the health and safety of both the parent and the baby.