Chlamydia is the most commonly reported bacterial sexually transmitted infection during pregnancy in the United States, with roughly 1 in 54 births affected based on 2018 national data. About 69,758 cases were reported among women giving birth that year, and rates have been slowly climbing. Because chlamydia rarely causes obvious symptoms, many pregnant women don’t know they have it until routine screening picks it up.
How Common It Is by Age and Background
Your risk of having chlamydia during pregnancy depends heavily on age. Among pregnant women under 20, the rate was approximately 7,288 per 100,000 births, nearly 20 times higher than among women over 40 (375 per 100,000). Outside of pregnancy, general population studies show chlamydia prevalence of about 4.7% among sexually active women aged 14 to 24, the group most commonly affected.
Racial disparities are significant. Black women had a rate of about 4,216 per 100,000 births, roughly four times the rate among white women (1,117) and nearly double the rate among Hispanic women (2,151). Women on Medicaid had a rate about five times higher than those with private insurance. Women who smoked during pregnancy had more than double the rate of nonsmokers. And women who delayed prenatal care or skipped it entirely had chlamydia rates about twice as high as those who started care in their first trimester.
Why It Matters During Pregnancy
Untreated chlamydia can increase the risk of preterm labor by two to four times. One study comparing treated versus persistently infected women found preterm birth rates dropped from 13.9% to 2.9% with treatment, a dramatic reduction. Treated women also delivered at later gestational ages on average (35.5 weeks versus 33.1 weeks for untreated women), which translates to meaningfully better outcomes for the baby.
Premature rupture of membranes, where the water breaks too early, is also more likely with untreated infection. Across several studies, treatment cut premature rupture rates roughly in half. One trial found the rate dropped from 16% to 6% with appropriate antibiotics.
For the baby, the risk of direct infection during a vaginal delivery is substantial. Approximately 30% to 50% of newborns born to mothers with active chlamydia will contract the infection during birth. Of those infected babies, 25% to 50% develop eye infections (neonatal conjunctivitis), and 5% to 20% develop pneumonia in their first weeks of life. Both conditions are treatable but potentially serious, especially for newborns.
Screening: Who Gets Tested and When
All pregnant women under 25 should be screened for chlamydia at their first prenatal visit. For women 25 and older, screening is recommended if they have risk factors: a new partner, more than one partner, a partner who has other partners or a known STI, inconsistent condom use, a previous STI, or a history of incarceration.
If you’re under 25 or have risk factors, you’ll be tested again during the third trimester. The standard test is a nucleic acid amplification test (NAAT), which is a simple urine sample or vaginal swab. These tests have sensitivity above 90% and specificity above 98%, making false results uncommon. Because chlamydia is so often silent, with most women experiencing no discharge, pain, or other symptoms, screening is the only reliable way to catch it.
What Happens If You Test Positive
Chlamydia during pregnancy is treated with antibiotics that are safe for the developing baby. Some commonly used antibiotics for chlamydia outside of pregnancy, like doxycycline, are not safe during pregnancy, so your provider will choose an alternative. Treatment is a short course, typically a single dose or a week-long regimen depending on the medication.
After finishing treatment, you’ll be retested about four weeks later to confirm the infection has cleared. This “test of cure” is especially important during pregnancy because the stakes of a persistent infection are high for both you and the baby. You’ll also be retested about three months after treatment, since reinfection is common if a partner wasn’t treated at the same time. Your sexual partner needs treatment too, or you’re likely to get reinfected before delivery.
What This Means Practically
If you’re pregnant and wondering whether chlamydia is something you should worry about, the answer is that it’s common enough to warrant routine screening but entirely treatable when caught. The infection itself causes no symptoms in most women, so there’s no way to know you’re clear without a test. Early prenatal care is one of the strongest protective factors: women who started care in the first trimester had significantly lower chlamydia rates than those who delayed, likely because early screening leads to early treatment before complications develop.
If you do test positive, treatment dramatically reduces the risks of preterm birth, early membrane rupture, and newborn infection. The key is getting screened early, completing any prescribed antibiotics, making sure your partner is treated, and following up with the repeat test to confirm the infection is gone.