The percentage of pregnant women in Ontario, Canada, screened for syphilis in the first trimester—which helps prevent transmitting the infection to a fetus—rose from 77% to 81% from 2018 to 2023, according to a study published last week in CMAJ, the journal of the Canadian Medical Association.

At the same time, the percentage of pregnant women who weren’t screened at all for syphilis fell from 10.9% to 5.5%, a drop of about 50%, according to the study of 551,706 pregnancies in 446,660 women.

In spite of that progress, the new study suggests that nearly one in five pregnant women in Ontario weren’t screened according to national and international guidelines, wrote the authors of the study, led by Sahar Saeed, PhD, an assistant professor of public health at Queen’s College in Kingston, Ontario.

Syphilis, a sexually transmitted infection (STI), can be catastrophic for a pregnancy, causing premature birth, low birth weight, anemia, stillbirth, and newborn death. Women can pass the infection to the fetus as early as the ninth week of pregnancy, the authors noted, making it imperative to screen and treat them as early as possible. 

Rates of syphilis in Ontario women age 15 to 39 ballooned from 2 per 100,000 women in 2014 to 54 per 100,000 women in 2023. Rates of congenital syphilis, which occurs when mothers transmit the infection to a fetus during pregnancy or delivery, grew from 0.3 per 100,000 live births to 14.5 per 100,000 live births. Congenital syphilis is preventable if pregnant women are tested and treated with antibiotics.

US seeing bigger increases in syphilis, congenital syphilis

Yet syphilis rates in Canada, which offers universal healthcare, are dwarfed by the syphilis epidemic in the United States, where funding for STI prevention and treatment has declined sharply in the past two decades.

The US Centers for Disease Control and Prevention (CDC) reported 81 syphilis cases per 100,000 girls and women ages 15 to 44 in 2024. In the same year, there were more than 3,900 cases of congenital syphilis, or 110 cases per 100,000 live births.

Owing to an “alarming” rise in syphilis cases in pregnant women and infants, the American College of Obstetricians and Gynecologists now recommends that healthcare professionals screen pregnant women syphilis at the first prenatal care visit, followed by universal rescreening during the third trimester and at birth. The medical society began recommending multiple screenings because it’s possible for pregnant women to be tested and treated for syphilis in the first trimester, but reinfected later in pregnancy, especially if their partner isn’t treated.