A CMV-positive sperm donor is someone who has previously been infected with cytomegalovirus, a common herpes-family virus, and now carries antibodies against it. On a donor profile, “CMV positive” almost always means the donor tested positive for IgG antibodies, which indicate a past infection that has resolved. It does not mean the donor is currently infectious. Roughly 45% to 100% of adults worldwide are CMV seropositive depending on the region, so encountering CMV-positive donors is extremely common.
What CMV Antibody Results Actually Mean
Sperm banks test donors for two types of CMV antibodies: IgM and IgG. These tell very different stories. IgM antibodies appear first during an active or recent infection. They typically decline within a few months as the immune system shifts to producing IgG antibodies. IgG antibodies persist for life and signal that the body has already fought off the virus and developed immunity.
A donor who is IgG positive and IgM negative has recovered from a past infection and is considered immunized, not actively infectious. This is the profile most sperm banks label simply as “CMV positive.” A donor with elevated IgM, on the other hand, may have a recent or active infection. Reproductive medicine guidelines recommend excluding donors with signs of active CMV infection until those markers resolve. Reputable sperm banks will not release samples from donors showing active infection.
One nuance worth knowing: about 25% of people who get a primary CMV infection still have detectable IgM antibodies four months later, and in some cases IgM can linger for over a year. That’s why banks may also use additional testing, like IgG avidity (which measures how tightly antibodies bind to the virus), to distinguish a genuinely new infection from leftover IgM. High avidity with positive IgM typically rules out a recent primary infection.
How Common CMV Is
CMV is one of the most widespread viruses in the human population. In Germany, a large national study found overall adult seroprevalence of about 57%, with women testing positive more often (62%) than men (51%). In many lower-income countries, seroprevalence exceeds 90%. Most people acquire CMV during childhood or young adulthood and never know it, because healthy immune systems suppress the virus without causing noticeable symptoms.
Because so many adults carry CMV antibodies, limiting your donor search to CMV-negative donors can significantly shrink your options. Whether that tradeoff makes sense depends on your own CMV status and risk tolerance.
The Actual Risk of Transmission Through Donor Sperm
The concern with using a CMV-positive donor isn’t about the donor’s health. It’s about whether the virus could be present in the semen sample and transmitted to the recipient, potentially reaching a developing fetus. The honest answer is that the exact risk remains unknown. The FDA mandates CMV screening for sperm donors, and the American Society for Reproductive Medicine recommends testing recipients as well, but no large studies have quantified the precise transmission rate from donor insemination.
Older research provides some reference points. Studies of cryopreserved semen from IgG-positive donors found detectable CMV DNA in about 8% of samples using PCR testing, while replication-competent virus (the kind that could actually cause infection) was found in roughly 4.5% of samples. Detecting virus in a sample, however, is not the same as transmission to the recipient. The gap between “virus present in frozen semen” and “recipient becomes infected” is not well characterized.
After a primary infection, CMV shedding in semen typically continues for several months but usually stops within about six months. This is one reason sperm banks quarantine samples and retest donors over time before releasing vials.
Why It Matters: Congenital CMV
The reason CMV gets special attention in fertility settings is the risk of congenital CMV infection, which occurs when the virus crosses the placenta during pregnancy. About 1 in 200 babies in the United States is born with congenital CMV. Of those, roughly 1 in 5 will develop birth defects or long-term health problems.
The most common serious outcome is hearing loss, which can be present at birth or develop gradually during early childhood. Other possible effects include developmental and motor delays, vision problems, seizures, and in severe cases, pregnancy loss. Babies born with symptomatic congenital CMV may show signs like jaundice, an unusually small head, low birth weight, an enlarged liver or spleen, or a rash.
The risk is highest when a woman contracts CMV for the first time during pregnancy (a primary infection). Women who were already CMV positive before pregnancy can occasionally reactivate the virus or encounter a new strain, but the risk of serious harm to the baby is substantially lower because existing antibodies provide partial protection.
Your CMV Status Changes the Equation
If you are CMV positive yourself (meaning you already carry IgG antibodies from a past infection), using a CMV-positive donor adds very little additional risk. Your immune system already knows how to suppress this virus. The scenario that reproductive specialists worry about is a CMV-negative recipient using a CMV-positive donor, because a primary infection during pregnancy carries the greatest chance of transmission to the fetus.
This is why many fertility clinics recommend testing your own CMV status before selecting a donor. If you’re CMV negative, you have a few options to consider. Some people choose a CMV-negative donor to avoid the question entirely. Others proceed with a CMV-positive donor after confirming the donor shows no signs of active infection (IgG positive, IgM negative), accepting that the residual risk appears to be very low based on available data. The ASRM has noted that the risk of CMV transmission and newborn infection from procedures like embryo transfer is extremely low, and affected infants in those cases appear to have no significant illness.
What Sperm Banks Do to Reduce Risk
FDA regulations require that all sperm donors be tested for CMV. If a donor tests reactive, the sperm bank must have standard operating procedures in place governing whether and how those samples can be released. Samples from donors deemed ineligible due to infectious disease testing must carry prominent warning labels including a biohazard symbol.
In practice, most major sperm banks handle CMV-positive donors by confirming the infection is past (IgG positive, IgM negative) and clearly labeling the donor’s CMV status on their profile so recipients can make an informed choice. Donors with evidence of active infection are typically deferred until their markers normalize. Some banks perform additional molecular testing on semen samples to check for viral DNA, adding another layer of screening beyond antibody tests alone.
The quarantine period that all frozen sperm undergoes (typically six months, after which the donor is retested for various infections) also works in favor of safety, since CMV shedding in semen after a primary infection generally resolves within that timeframe.