Trichomoniasis (also called “trich”) is a sexually transmitted disease (STD) caused by a parasite. It affects an estimated 3.7 million people in the United States, making it the most common sexually transmitted disease.

The infection is most common in women. Older women are more likely to be infected than younger women. If left untreated, a trichomoniasis infection can last for several months or years. Its symptoms can make sex unpleasant. But for pregnant women, it can cause serious childbirth complications.

Pregnant women with trichomoniasis are at higher risk of their water breaking too early. This is also known as premature rupture of the membranes. Pregnant women are also at higher risk of delivering their babies prematurely, or before 37 weeks.

Babies of mothers with trichomoniasis are more likely to have a birth weight of less than 5.5 pounds. In rare cases, female babies can contract the infection as they move through the birth canal.

Premature birth and low birth weight are two of the top three causes of death for babies.

According to the Centers for Disease Control and Prevention (CDC), 70 to 85 percent of people with trichomoniasis don’t experience any symptoms.

Symptoms in men are rare, but they may experience:

  • irritation inside the penis
  • a burning sensation while urinating or after ejaculating
  • discharge from the penis

In women, trichomoniasis can cause:

  • a fishy genital odor
  • large amounts of white, gray, or green vaginal discharge
  • genital itching
  • pain while urinating or having sex

Trichomoniasis is caused by a microscopic parasite called Trichomonas vaginalis. It passes from person to person during sexual intercourse. The incubation period between exposure and infection is about five to 28 days.

Some people are more at risk of contracting trichomoniasis than others. Those with the greatest risk of infection include people:

  • with multiple sexual partners
  • who have had other STDs in the past
  • who have had trichomoniasis in the past
  • who have sex without condoms

To test for trichomoniasis, a doctor will use a microscope to look for the parasite in a sample. For women, the sample source is vaginal discharge. For men, the sample source is urine. A doctor may then run further tests on the sample to confirm the presence of the parasite. These include a culture test, nucleic acid amplification test, or rapid antigen test.

Pregnant women displaying any symptoms of the infection should see their doctors right away. They’re not usually tested for trichomoniasis, so the infection may go unnoticed and could harm their baby.

Pregnant women with trichomoniasis are at greater risk of:

  • premature labor and delivery
  • having a baby with a low birth weight
  • transmitting trichomoniasis to a female baby during delivery

All women with trichomoniasis may be more likely to contract HIV.

Doctors usually treat trichomoniasis with a very large dose of antibiotics. One of two antibiotics is typically used: metronidazole (Flagyl) or tinidazole (Tindamax). You and your partner will both need treatment. Also, you both must avoid sexual intercourse until the infection clears up.

You should not consume alcohol for 24 hours after taking metronidazole or 72 hours after taking tinidazole. It can lead to severe nausea and vomiting.

After treatment, it usually takes about a week for a trichomoniasis infection to clear up. Most people make a full recovery.

Like all sexually transmitted diseases, the only way to fully prevent trichomoniasis is to abstain from sex. Women who are sexually active can decrease their risks of infection by making sure their partners use a condom correctly every time during sex.