Chlamydia can affect fertility in both women and men, but the damage depends heavily on whether the infection is caught and treated early. Left untreated, chlamydia triggers inflammation that scars the reproductive tract, potentially blocking the fallopian tubes or damaging the structures that transport sperm. About 75% of women and 50% of men with chlamydia have no symptoms at all, which means the infection often goes undetected long enough to cause harm.
How Chlamydia Damages the Reproductive Tract
Chlamydia doesn’t cause infertility directly. The real threat is what happens when the infection spreads beyond the cervix or urethra into the deeper reproductive organs. In women, this means pelvic inflammatory disease, or PID, an infection of the uterus, fallopian tubes, and surrounding tissue. PID creates scar tissue both inside and outside the fallopian tubes, which can partially or fully block them. When a tube is blocked, an egg can’t reach the uterus, and sperm can’t reach the egg.
Roughly 17% of women with untreated chlamydia will develop PID, including cases that go undiagnosed because the symptoms are mild or absent. About 12% of women who have a single episode of PID suffer enough tubal damage to become infertile. After three episodes, that number jumps to 50%. Each round of infection and inflammation layers on more scarring, making the damage cumulative and increasingly difficult to reverse.
The Risk of Ectopic Pregnancy
Scarred or partially blocked fallopian tubes don’t just prevent pregnancy. They also raise the risk of ectopic pregnancy, where a fertilized egg implants inside the tube instead of the uterus. This is a medical emergency that can cause life-threatening bleeding.
The risk scales with the number of infections. Women who’ve had two chlamydia infections face roughly double the odds of ectopic pregnancy compared to women who’ve had one. Women with three or more infections have about 4.5 times the odds. Repeated infections also dramatically increase the likelihood of developing PID itself: three or more chlamydia infections raise the risk of PID by more than six-fold.
Effects on Male Fertility
Chlamydia’s impact on male fertility is less talked about but real. The infection is responsible for 40 to 80% of cases of epididymitis, an inflammation of the coiled tube behind each testicle that stores and carries sperm. When this structure becomes inflamed and scarred, it can physically obstruct the path sperm need to travel. In severe cases, this leads to testicular shrinkage and a complete absence of sperm in the ejaculate.
Even without a full blockage, chlamydia directly damages sperm cells. Infected men tend to have lower sperm concentration, reduced motility (how well sperm swim), and more abnormally shaped sperm. The good news: after successful antibiotic treatment, sperm quality improves significantly. One analysis found greater than 57% improvement in concentration and motility after the infection cleared, though recovery wasn’t complete in every measure.
Risks During Pregnancy
If you’re already pregnant, an active chlamydia infection carries its own set of risks. A population-based study found that pregnant women with chlamydia had a four-fold increased risk of very early preterm delivery (before 32 weeks) and nearly triple the risk of delivery before 35 weeks, even after accounting for factors like age, smoking, and ethnicity. Roughly 15% of very early preterm births in the study population were attributable to chlamydia infection.
The infection can also pass to the baby during vaginal delivery, potentially causing eye infections or pneumonia in the newborn. Reassuringly, the study found no significant link between chlamydia and miscarriage, stillbirth, or low birth weight.
Why Screening Matters So Much
Because most chlamydia infections produce no symptoms, routine screening is the primary line of defense against fertility damage. The CDC recommends annual chlamydia testing for all sexually active women under 25, and for older women with risk factors like a new partner or multiple partners. For men, routine screening isn’t broadly recommended but is advised in higher-risk settings. More frequent testing may be appropriate depending on your sexual activity and number of partners.
The logic is straightforward: catching and treating an infection before it ascends into the upper reproductive tract prevents the scarring that leads to infertility. A simple course of antibiotics clears the bacteria. What antibiotics can’t do is undo scar tissue that has already formed. That’s why timing matters more than almost anything else. A chlamydia infection treated within days or weeks poses minimal fertility risk. One that silently persists for months has far more opportunity to cause lasting damage.
Fertility Options After Tubal Damage
If chlamydia has already caused tubal blockage, IVF is typically the recommended path to pregnancy. IVF bypasses the fallopian tubes entirely: eggs are retrieved directly from the ovaries, fertilized in a lab, and transferred to the uterus. A study comparing IVF outcomes in women with a history of chlamydia-related tubal damage to women without that history found no significant difference in live birth rates per cycle, about 36-37% in both groups. Fertilization rates and implantation rates were also comparable.
Women with prior chlamydia infections did have higher rates of tubal obstruction and a condition called hydrosalpinx, where fluid collects in a blocked tube. When hydrosalpinx is present, it’s often surgically removed or clipped before IVF to improve outcomes. But once that’s addressed, chlamydia-related tubal damage does not appear to reduce IVF success compared to other causes of infertility.