It can be confusing and frustrating when your doctor says all your tests look “normal,” but you still can’t get pregnant. If this has happened to you, you’re not alone. Many women are told they have “unexplained infertility” simply because routine tests don’t show what’s really going on in the uterus.
One important answer science has uncovered is a hidden virus called HHV-6A. This virus does not appear on regular blood tests, hormone tests, or ultrasounds. Instead, it hides inside the cells of the uterine lining, where standard testing never looks.
In a major study, researchers checked the uterus tissue of women with unexplained infertility and found HHV-6A in 43 out of 100 women. They found the virus in 0 out of 100 fertile women they tested. This means the problem may not be with your eggs, your hormones, or your partner’s sperm—it may be something inside the lining of your uterus that no one tested.
When HHV-6A is active, it can change the immune balance inside the uterus. This can make it harder for an embryo to attach, even when the embryo is strong and healthy. That’s why your tests can look completely normal, yet implantation still doesn’t happen.
Finding HHV-6A often requires a test that looks at endometrial cells—either through a clinic biopsy or a menstrual-fluid test that collects cells naturally shed from the uterus.
If your tests look normal but pregnancy still isn’t happening, the next question is:
“Why does HHV-6A affect the uterus so much?”
Read this article next to learn more: “The Uterus Micro-Environment: Why Implantation Fails.”
References
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Marci R, Gentili V, Bortolotti D, et al. Presence of HHV-6A in endometrial epithelial cells from women with primary unexplained infertility. PLOS ONE. 2016.
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Knox K, Doody K. Prospective evaluation of human herpesvirus 6 (HHV-6) in endometrial biopsies of women with repeat implantation failure. ASRM Poster. 2019.
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Komaroff AL, Pellett PE. Human Herpesviruses 6 and 7. StatPearls; NCBI Bookshelf. 2021.