CMV is a common herpesvirus that infects most people by middle age, often without causing noticeable symptoms. Once acquired, the virus remains dormant in the body for life. In Vitro Fertilization (IVF) combines an egg with sperm outside the body to form an embryo before transfer into the uterus. The intersection of CMV status and IVF is important because a first-time infection during pregnancy presents risks to the developing fetus. Fertility clinics routinely screen prospective parents to determine their CMV status and tailor treatment plans accordingly.
Impact on Gamete and Embryo Viability
The question of whether a CMV infection affects the physical process of IVF, such as the quality of eggs or sperm, has been a focus of research. Some studies on male reproductive function suggest that the presence of CMV DNA in semen is associated with a decrease in sperm count, motility, and normal morphology. However, other analyses have found no significant difference in fertilization rates, pregnancy rates, or live birth rates between couples using sperm from CMV-positive versus CMV-negative men.
CMV DNA has been detected in semen, suggesting a potential for the virus to be present during fertilization procedures. Standard laboratory procedures for preparing sperm for IVF or Intracytoplasmic Sperm Injection (ICSI), such as sperm washing, are thought to reduce the viral load significantly. For the female side, some data indicates that CMV IgG positivity, which signals a past infection, may correlate with a lower number of retrieved oocytes and a reduced clinical pregnancy rate following IVF. Conversely, studies attempting to detect CMV DNA directly in oocytes or embryos have not found evidence of the virus, suggesting that transmission through the gamete or early embryo itself is unlikely.
Congenital Transmission Risk in IVF Pregnancies
The primary concern regarding CMV in the context of IVF is the risk of mother-to-child transmission once a pregnancy is established, a risk that is independent of how conception occurred. The risk of passing the virus to the fetus is highest, approximately 30 to 40%, when a woman contracts the virus for the first time, known as a primary infection, while she is pregnant. This risk is especially concerning if the primary infection occurs during the first trimester, as this is associated with the most severe outcomes for the baby.
Maternal immunity from a prior infection does offer a substantial protective effect against severe fetal disease. When a woman who was previously CMV-positive experiences a recurrent infection during pregnancy, the transmission risk is much lower, typically less than 2%. A recurrent infection can still lead to congenital CMV (cCMV) disease, though the severity is generally less than that following a primary infection.
Congenital CMV is the most common infectious cause of birth defects in the United States, and it can result in long-term health issues. Consequences include sensorineural hearing loss, vision problems, and developmental delays. The potential for cCMV and its lifelong impact is the main reason fertility clinics incorporate CMV screening into their standard protocols. If a primary infection is suspected during the IVF cycle or early pregnancy, immediate monitoring and counseling become necessary to assess the fetal risk.
CMV Screening Protocols in Fertility Clinics
Fertility clinics screen for CMV using blood tests to detect specific antibodies, a process known as serology. The two main antibodies tested are Immunoglobulin G (IgG) and Immunoglobulin M (IgM). IgG antibodies indicate a past infection, meaning the individual has developed immunity.
IgM antibodies suggest a recent or active infection, though IgM can persist for months or reappear during a recurrent infection. To differentiate a recent primary infection from a past one, clinics may use an IgG avidity assay. Low avidity suggests a very recent primary infection, while high avidity indicates an infection that occurred remotely (typically more than three to six months prior). Both partners are screened to understand the potential exposure risk to the CMV-negative partner, particularly the woman, during treatment and subsequent pregnancy.
Clinical Guidance Based on Serostatus
A woman’s serostatus dictates the clinical guidance provided by the fertility team to minimize the risk of cCMV.
Guidance for CMV-Negative Women
For women who test CMV-negative (no past exposure), counseling focuses on prevention strategies during the IVF cycle and pregnancy. This involves strict adherence to hygiene practices, such as diligent handwashing, especially after contact with the urine or saliva of young children who frequently shed the virus.
Guidance for Active Infection
If a patient has an active infection, indicated by a positive IgM result, the clinic recommends postponing the embryo transfer, usually for six to twelve months. This waiting period allows the active viral phase to resolve and IgM levels to decline, significantly reducing the risk of transmission to the fetus.
Guidance for Donor Gametes
When using donor gametes, CMV status matching is a standard safety measure. Fertility clinics mandate CMV screening for all sperm and egg donors. The preferred protocol is to match CMV-negative recipients with CMV-negative donors to eliminate the risk of transmission through the donor material and prevent a primary maternal infection. While CMV can be present in semen, the risk of transmission is very low with washed and prepared sperm, and negligible with donated eggs or embryos due to laboratory washing and handling procedures.