Yes, you can get pregnant with a bacterial infection, but certain infections can make conception harder and raise the risk of miscarriage if you do conceive. The impact depends entirely on which infection you have, where it is, and how long it has gone untreated. A common condition like bacterial vaginosis (BV) won’t necessarily stop you from getting pregnant, but it roughly doubles the risk of first-trimester miscarriage. Sexually transmitted infections like chlamydia or gonorrhea pose a bigger long-term threat by potentially damaging your reproductive organs.
How Bacterial Infections Affect Conception
Bacterial infections in the vagina or cervix can interfere with pregnancy in several ways, though none of them make conception impossible. The most direct effect is on the environment sperm need to travel through. Your cervical mucus normally becomes thin and slippery around ovulation, creating a path for sperm to reach the egg. Infections like BV can change the consistency of this mucus, making it thicker or abnormal, which is harder for sperm to swim through. Think of the difference between swimming through water and swimming through mud.
Infections also change vaginal pH. Sperm function best in a narrow pH range, roughly 6.5 to 7.5. When an infection pushes pH too far outside that window, sperm motility drops significantly. Animal studies show that in infected conditions, sperm stayed motile for only about two minutes compared to three minutes in healthy conditions, and sperm survived in the reproductive tract for just two to three days instead of four to five. That shorter survival window means fewer viable sperm are present when ovulation occurs.
In women undergoing fertility treatments, BV was associated with lower ongoing pregnancy rates (11% vs. 20% in BV-negative women), though the difference wasn’t large enough to be statistically conclusive. The more striking finding was the miscarriage rate: 60% of pregnancies in BV-positive women ended in miscarriage, compared to 25% in BV-negative women.
The Miscarriage Risk With BV
BV is the infection most closely studied in relation to early pregnancy loss, and the numbers are consistent across research. A cohort study tracking women from conception found that 36.1% of women with BV miscarried in the first trimester, compared to 18.5% of women with normal vaginal flora. After adjusting for age, smoking, and pregnancy history, BV was associated with roughly twice the risk of first-trimester miscarriage.
The risks extend beyond early loss. BV identified before 16 weeks of pregnancy has been linked to preterm labor, with reported odds ratios as high as 6.9 in some studies. It’s also associated with low birth weight and postpartum uterine infections. These risks are highest when BV is present early in pregnancy and left untreated.
STIs and Long-Term Fertility Damage
Chlamydia and gonorrhea pose a different kind of threat. These bacteria can climb from the cervix into the uterus and fallopian tubes, triggering pelvic inflammatory disease (PID). Gonorrhea, in particular, causes a cascade of inflammation inside the fallopian tubes that destroys the tiny hair-like cells lining the tubes, strips away the inner surface, and eventually creates scar tissue that can block the tubes entirely. This process is called salpingitis, and it can happen with mild or even unnoticeable symptoms.
The fertility consequences of PID are significant. Among women who have been treated for PID, nearly 25% experience infertility, about 1.8 times the rate of women who have never had it. Tubal scarring can also increase the risk of ectopic pregnancy, where a fertilized egg implants in the fallopian tube instead of the uterus. Unlike BV, which mainly affects the conditions around conception, tubal damage from STIs can make pregnancy physically impossible without medical intervention like IVF.
Infections You Might Not Know About
Many bacterial infections that affect fertility produce no obvious symptoms. BV sometimes causes a fishy odor or grayish discharge, but it can also be completely silent. Chlamydia is notorious for causing no symptoms at all in the majority of women who have it. This is part of what makes these infections so damaging: they can quietly cause inflammation and tissue changes for months or years before anyone notices a problem.
Bacterial infections can also affect the male partner. Men with asymptomatic bacterial infections in their semen showed significantly more immotile sperm, fewer normally shaped sperm, and higher levels of immune cells that can damage sperm. One bacterium in particular, Enterococcus faecalis, was associated with over four times the odds of reduced sperm concentration. If you’ve been trying to conceive without success, testing both partners for infections is worth considering, even when neither of you has symptoms.
Treatment Before and During Pregnancy
The good news is that most bacterial infections respond well to antibiotics, and treating them before or during pregnancy is generally safe. The standard antibiotic used for BV, metronidazole, has been studied extensively in pregnant women across multiple large studies, and no evidence of harm to developing babies has been found. The CDC considers it a low-risk treatment during pregnancy.
Not all treatment options carry the same safety profile, though. Tinidazole, another common BV treatment, should be avoided during pregnancy based on animal studies showing moderate risk. If you’re actively trying to conceive or already pregnant, your treatment options may be narrower, but effective and safe choices exist.
For STIs like chlamydia and gonorrhea, early treatment is critical because the goal is to stop the infection before it reaches the upper reproductive tract. Once scarring has formed in the fallopian tubes, antibiotics can clear the bacteria but can’t reverse the structural damage. This is why routine STI screening matters so much for anyone planning a future pregnancy.
What This Means If You’re Trying to Conceive
If you suspect or know you have a bacterial infection, getting it treated before trying to conceive gives you the best odds of both getting pregnant and staying pregnant. BV in particular is worth screening for because it’s common (affecting roughly 1 in 3 women of reproductive age in the U.S.) and treatable, yet it meaningfully increases miscarriage risk when present during early pregnancy. A simple test at a routine appointment can identify it.
If you’ve already been trying to conceive without success, a full screening for vaginal, cervical, and sexually transmitted infections is a practical first step, especially before pursuing fertility treatments. Studies of women undergoing IVF found that those who tested positive for BV had lower success rates and higher pregnancy loss, suggesting that treating the infection before starting a cycle could improve outcomes. The same logic applies to natural conception: a healthy vaginal environment with the right pH, the right mucus consistency, and no active inflammation gives sperm the best chance of reaching the egg and gives a fertilized egg the best chance of surviving those critical first weeks.