Risk of Mother-Child Transmission of Syphilis Is Elevated if the Women Has Clinical Signs of Disease

Lisa Remez, Guttmacher Institute

First published online:

Four percent of Bolivian women giving birth to live-born children have laboratory-confirmed maternal syphilis. According to a study project that involved maternity patients in seven hospitals in Bolivia,1 14% of the live-born infants born to infected women had confirmed congenital syphilis. Women with less than a high school education and those with a history of syphilis were more likely, once other potentially confounding factors were controlled, to have been diagnosed with syphilis at delivery than were other women. In contrast, women who had watched television in the previous week (a proxy for socioeconomic status) were less likely than others to have syphilis. Infected women with clinical signs of disease were more likely to transmit syphilis to their children.

Maternity patients who delivered from June through November 1996 in seven participating hospitals in the cities of La Paz, El Alto and Cochabamba were eligible for the study, which was designed to identify the factors affecting the risk of maternal and congenital syphilis. Overall, 1,428 women with a live birth agreed to participate.

Women and their infants were tested for syphilis at the time of delivery. Blood samples were taken from women and from their newborn at birth, and hospital staff were trained to analyze the samples on-site using rapid plasma reagin testing. The samples were sent for both repeat testing and for additional confirmatory testing to one of two established reference laboratories in Bolivia, to assess the accuracy of the on-site diagnoses made by the newly trained hospital staff.

Moreover, a small proportion of the blood samples, and the umbilical cord samples collected from babies whose mothers had syphilis, were sent to the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta for further testing. The researchers examined standardized prenatal records to determine whether women had been tested for syphilis during a prenatal care visit.

Most of the women (76%) had received some prenatal care, but only 17% had documentation of syphilis testing during their pregnancy. Overall, 61 women (4%) tested positive for syphilis at delivery; only 5% of these women had physical signs (such as rash or genital ulcers) indicative of syphilis infection. (Forty-three additional maternity patients whose babies were stillborn also participated in the study; 11 of these women--26%--tested positive for syphilis at the time they delivered.) The rapid results from on-site hospital testing agreed with the Bolivian reference laboratory results and with the CDC results at least 94% of the time.

Bivariate analysis showed that a confirmed diagnosis of maternal syphilis was significantly more likely if the woman spoke an indigenous language and if she had not finished high school or if her steady partner had not done so. That likelihood was also increased if she had not received prenatal care, if she had a history of syphilis, if she earned a below-average monthly income, if she had had more than one partner during her pregnancy and if she had not watched television during the past week.

Once the effects of all of these variables were controlled for, only four were independently associated with the risk of a laboratory-confirmed syphilis diagnosis among women delivering a live-born child. Three factors significantly raised that risk--not having finished high school (odds ratio, 3.1), having had a previous diagnosis of syphilis (6.7) and having had more than one partner during pregnancy (28.5). One factor, having watched television in the past week, significantly lowered the likelihood of maternal syphilis (odds ratio, 0.5).

Among the babies born to women with syphilis, eight of the 57 whose umbilical cords were tested (14%) were confirmed as having congenital syphilis. Mothers whose children were infected were more likely than those whose children were not to have physical signs of syphilis, and they were less likely to have a stable partner at the time at delivery; the two groups of women, however, did not differ by language spoken at home, by educational attainment, by receipt of prenatal care, by area of residence (urban or rural) or by age. Among infants born to women with syphilis, those who had a confirmed diagnosis were more likely than those who did not to be underweight at birth and to be born prematurely.

According to the investigators, the study had several limitations that might lead to an underestimate of the incidence of maternal and congenital syphilis--its hospital-based setting in a country where 40% of births occur outside of hospitals; a low participation rate at some hospitals; and higher rates of low birth weight or prematurity (which may be caused by syphilis) among nonparticipants than among participants.

The researchers note that high rates of agreement between the results of the participating hospitals and the reference laboratories led to the development of a national syphilis prevention program in Bolivia involving free routine syphilis testing for pregnant women and free treatment with penicillin. They recommend that programs in other resource-poor settings adopt the following measures: offer low-cost on-site syphilis testing during prenatal care to yield same-day results, followed by immediate treatment; teach providers that in high-prevalence areas, treatment can be initiated on a diagnosis from rapid plasma reagin alone (without additional confirmatory testing); treat any infant, with or without symptoms, born to a woman diagnosed with syphilis at delivery; develop a culturally appropriate partner-notification system; and devise a national reporting system of all cases of maternal and congenital syphilis. --L. Remez


1. Southwick KL et al., Maternal and congenital syphilis in Bolivia, 1996: prevalence and risk factors, Bulletin of the World Health Organization, 2001, 79(1):33-42.