Trichomoniasis in pregnancy is a treatable infection caused by the parasite Trichomonas vaginalis that's linked to preterm birth and low birth weight if left untreated. Oral metronidazole is the standard treatment and is considered safe across all trimesters. Many infected people have no symptoms, so screen rather than waiting for signs.
most common curable STI
metronidazole / tinidazole
retest
| Item | Value |
|---|---|
| Estimated US infections | ~2.6 million — most common curable STI |
| Have no symptoms | ~70% |
| Cure | >90% — metronidazole / tinidazole |
| Reinfected within 3 mo | ~1 in 5 — retest |
Why trichomoniasis matters when you're pregnant
Trichomoniasis is the most common curable non-viral STI in the US, with an estimated 2.6 million infections, and it lands disproportionately on women, who account for over 80% of cases Sex Transm Dis, 2018. The infection comes from a single-celled protozoan parasite, Trichomonas vaginalis, that lives in the lower genital tract and spreads during sex CDC. In a pregnant body, the local inflammation it causes can irritate the cervix and vaginal lining and raise the chance of complications that affect the pregnancy itself.
About 70% of infected people have no signs or symptoms at all. You can carry it through much of a pregnancy and feel completely normal. When symptoms do show up in women, they include itching, burning, redness or soreness of the genitals, discomfort while urinating, and a clear, white, yellowish or greenish discharge with a fishy smell. Because that fishy discharge overlaps with another common condition, it's worth understanding the difference between trichomoniasis vs bacterial vaginosis. They're treated differently and a swab tells them apart.
What are the risks to the baby?
Untreated trichomoniasis in pregnancy increases the chance of two outcomes doctors watch closely: preterm birth (delivery before the pregnancy reaches full term) and low birth weight (a baby born smaller than expected for their gestational age) CDC STI Tx Guidelines, 2021. A baby born early or small faces a higher risk of breathing trouble, feeding difficulty, and time in newborn intensive care, so the goal is to catch and clear the infection during prenatal care.
There's a second, less obvious risk. Trichomoniasis inflames the genital tissue, and that inflammation makes it easier both to acquire and to pass on other sexually transmitted infections, including HIV. In a pregnancy, an added HIV risk is significant, since HIV can be transmitted to the baby. Treating trich removes one of the doorways other infections use.
When should you be screened in pregnancy?
Because most infections are silent, screening is how trich gets found. Routine annual screening is specifically recommended for asymptomatic women living with HIV, who are at higher risk. For other pregnant patients, testing is typically prompted by symptoms or a partner's diagnosis, and many clinicians test if there's discharge or known exposure. If you've had a recent new partner, ask about when to test after exposure so the timing of your swab doesn't miss the infection too early.
The test itself is quick. A clinician collects a vaginal swab, and modern molecular (NAAT) tests are sensitive enough to find the parasite even when you have no symptoms. That's a big improvement over the old method of looking for moving organisms under a microscope, which missed many cases. If you want the full picture of how the lab work is done and what each method detects, see trichomoniasis testing & diagnosis. Routine testing catches infections that produce no symptoms, which matters most during pregnancy. You can also get tested if you're between prenatal visits and want to confirm.
Safe treatment in pregnancy
The standard treatment is oral metronidazole, used across all trimesters. For women, the recommended course is metronidazole 500 mg orally twice daily for seven days. The 2021 guidelines moved women off the older single 2 g dose for a concrete reason: in a randomized trial, about 19% of women given the single dose were still infected at follow-up, versus about 11% on the seven-day course Muzny et al., Sex Transm Dis. The multi-day course roughly halved the retest-positive rate, so it's now preferred for women, pregnant or not.
Two practical rules matter as much as the prescription. Avoid alcohol during metronidazole treatment, and with tinidazole, the alternative: the combination triggers a disulfiram-like reaction with flushing, nausea, and vomiting. Treat all sex partners at the same time, even if they feel fine, or you'll pass it back and forth. Men are commonly asymptomatic and are treated with a single 2 g dose of metronidazole; tinidazole 2 g as a single dose is an alternative for either partner.
| Who | Recommended regimen | Why |
|---|---|---|
| Women (incl. pregnant) | Metronidazole 500 mg twice daily for 7 days | Halved retest-positive rates vs. the single dose |
| Men | Metronidazole 2 g as a single dose | Standard, effective in men |
| Alternative (either) | Tinidazole 2 g as a single dose | Option when metronidazole isn't suitable |
Finish the entire course even once symptoms ease, because stopping early lets surviving parasites rebound. Reinfection is common, so guidelines advise retesting sexually active women about three months after treatment. For the full rundown on dosing, side effects, and what to expect, see trichomoniasis treatment.
Reducing transmission around delivery
The strongest move you can make to lower risk at delivery is to have the infection cleared before you go into labor, which is the rationale for screening and treating during prenatal care. Treating your partner at the same time prevents you from picking it back up before the baby arrives. Between treatment and delivery, condoms used every time lower the chance of reinfection or acquiring another STI through the rest of the pregnancy.
When to see a clinician
Bring it up at any prenatal visit if you notice unusual discharge, genital itching or soreness, or burning when you urinate, or if a partner has been diagnosed with trichomoniasis. Don't wait for symptoms to worsen and don't try to ride it out, because the pregnancy risks come from the infection persisting rather than from how bad it feels. If you've started treatment and your symptoms haven't cleared after finishing the full course, that's also a reason to check back in.