The S.T.D. has gained ground among all women in the U.S., including those who are expecting.
Syphilis continues to make a dismaying comeback in the United States.
Between 2012 and 2016, the rate of primary and secondary syphilis among women increased 111 percent. Over the same period, the rate of congenital syphilis increased by 87 percent.
The sexually transmitted disease is caused by infection with the bacterium Treponema pallidum. The bacterium also can be passed from mother to child during pregnancy or birth.
Up to 40 percent of infants with syphilis are stillborn. The rest appear normal at birth; if left untreated, however, they may develop a number of serious symptoms, from bone pain to deafness and blindness.
Infected babies are treated with penicillin. Infants who picked up the bacterium while passing through the birth canal generally fare better than those infected during pregnancy.
The number of reported syphilis cases in women — including primary and secondary stages, and latent stage, when infection is much less easily transmitted — rose to 14,838 in 2016 from 9,551 in 2012, an increase of 55 percent, according to a study published in the journal Obstetrics and Gynecology.
Over the same period, the number of cases in pregnant women increased 61 percent, to 2,508 from 1,561.
The increases occurred in all age groups, among all racial and ethnic groups, and in every region of the country. The greatest increases were among women in their twenties, non-Hispanic black women, and women who live in the South.
Only half of pregnant women reported any of the known risk factors, among them drug use, a history of sexually transmitted disease, or more than one sex partner in the past year.
“All women must be tested,” said the study’s senior author, Dr. Sarah Kidd, a medical officer at the Centers for Disease Control and Prevention. “If you’re only trying to weed out women with typical risk factors, you’re going to miss a lot of women.”
The C.D.C. recommends screening at the first prenatal visit. Because some women become infected after the initial test, women should be screened again during the third trimester and again at delivery, especially those women living where prevalence is high.
Treatment of pregnant women with penicillin is up to 98 percent effective in preventing congenital syphilis.
“The incidence of syphilis has been at an all-time low over the past 20 years,” Dr. Kidd said. “Some recently trained physicians have never seen it. But it’s making a comeback, and physicians should be aware of it.”