In Vitro Fertilization (IVF) is a fertility treatment where an egg and sperm are combined in a laboratory, and the resulting embryo is transferred into the uterus. Miscarriage is the unexpected loss of a pregnancy before 20 weeks of gestation. Many considering IVF wonder how this process impacts the risk of miscarriage.
Understanding Miscarriage
Miscarriage is common, affecting 10% to 20% of known pregnancies before 20 weeks. Most occur in the first trimester (first 13 weeks). The most frequent reason for early miscarriage is a chromosomal abnormality in the developing embryo, occurring randomly during conception or early cell division.
While chromosomal issues account for a large percentage of miscarriages, other factors can contribute. These include placental problems, infections, hormonal imbalances, and structural abnormalities of the uterus. Lifestyle factors such as smoking, excessive alcohol consumption, and medical conditions like uncontrolled diabetes or thyroid disease can also increase risk. However, most miscarriages are not caused by anything the pregnant individual did or did not do.
The Relationship Between IVF and Miscarriage Risk
IVF itself does not inherently reduce or significantly increase miscarriage risk for all patients. The underlying reasons for infertility often contribute more to the miscarriage risk than the IVF procedure. Patients undergoing IVF frequently have pre-existing factors that elevate their risk, such as advanced maternal age, diminished ovarian reserve, or specific medical conditions.
Advanced maternal age is a primary driver of miscarriage risk in both natural and IVF pregnancies. As a woman ages, egg quality and quantity decline, leading to a higher likelihood of chromosomal abnormalities. Miscarriage rates for women over 35 undergoing IVF can be significantly higher than for younger women, reflecting this age-related decline. Overall, IVF miscarriage rates are often similar to or only slightly higher than in natural pregnancies, largely because IVF patients tend to have more risk factors.
IVF cannot prevent miscarriages caused by severe chromosomal abnormalities incompatible with life. However, it offers tools that can indirectly influence outcomes. For example, assessing embryo quality during IVF can help identify embryos with a lower likelihood of success.
How IVF Procedures Can Influence Miscarriage Risk
Specific aspects of the IVF process can influence miscarriage rates. Embryo quality and selection are important; embryologists often choose embryos that appear morphologically normal for transfer. While visual assessment guides selection, it does not guarantee chromosomal normalcy.
The number of embryos transferred can also impact outcomes. Transferring multiple embryos increases the chance of multiple pregnancies, which carry a higher risk of complications, including miscarriage. For this reason, single embryo transfer is often recommended to optimize safety and success.
The choice between fresh and frozen embryo transfers may also influence miscarriage rates, with some research suggesting differences. A healthy uterine environment is crucial for successful implantation and continued pregnancy, and certain uterine issues can increase miscarriage risk regardless of how conception occurs.
When IVF is a Strategy for Recurrent Miscarriage
IVF can be a targeted strategy for individuals experiencing recurrent miscarriage (two or more consecutive pregnancy losses). In these cases, Preimplantation Genetic Testing for Aneuploidy (PGT-A) is utilized.
During PGT-A, cells are removed from an embryo for genetic analysis, allowing only chromosomally normal (euploid) embryos to be selected for transfer. Since a significant proportion of recurrent miscarriages are attributed to chromosomal abnormalities, PGT-A can substantially improve the chances of a successful pregnancy and live birth for couples with a history of recurrent loss.