Prenatal syphilis testing is an essential preventative measure to halt the transmission of maternal syphilis infection to the fetus, which can lead to congenital syphilis in infants and stillbirths [1]. In this study, providers tested 82% of pregnancies that resulted in live births from 2014 to 2016. Providers’ adherence increased over time from 71.1% in 2014 to 86.6% in 2016.
Although women who were classified as high risk were screened more frequently, adherence to screening at 28 weeks and delivery was poor. In agreement with previous studies, we found that those with government insurance such as Medicaid and Medicare were tested more frequently than women with commercial insurance [25].
Providers’ adherence in this study was lower than previous studies [8,9,10] including one from Indianapolis [13] (95-98.2%). These studies were published over 15 years ago. Although there were differences in study populations, it is also possible that providers decreased testing practice after CDC’s efforts to eliminate syphilis beginning in 1999 [26].
We found that 19% of women were not tested for syphilis at any time during pregnancy. These are missed opportunities to detect and treat syphilis infections. A Louisiana study examining opportunities to prevent CS found that one-third of CS cases could have been prevented if prenatal syphilis testing was done [27]. Another study found that over one-third of women who had a stillbirth were not screened for syphilis [17, 28]. Diagnoses must be followed by timely treatment. However, Kidd et al. (2018) found that most infants with congenital syphilis were born to mothers who tested positive and were diagnosed with syphilis but not treated [29]. Our study was unable to assess treatment because treatment data is incomplete in the INPC.
In addition, our study also indicates that 41 women had syphilis infection based on serology from 2014 to 2016. In Marion County, during this time, there were 365 cases of early syphilis, of which 24 were women, and 189 late latent syphilis cases, of which 66 were women [4]. In the state, a total of 23 congenital syphilis cases were reported during the study period [3, 30]. Specifically, in Marion County, a total of 5 CS cases were observed between 2014 and 2016, with these cases occurring in 2016. Although we found five pregnancies with serologic diagnosis of syphilis less than thirty days before delivery, we cannot confirm that these are the same CS cases reported because our data were de-identified.
Contrary to Schrag et al. (2003), we found that providers were more likely to test women at higher risk, as defined by zip code of residence, than the overall population [8]. The increase in testing observed within the high-risk population is consistent with the CDC prenatal testing guidance [24]. However, despite the recommendation from the CDC and ACOG, only 27% of high-risk women were tested at delivery, and 9% were tested only at delivery. Alarmingly, our study found that over 7.3% of the women that tested positive for syphilis during the study period were tested only at delivery. These data indicate that providers do not fully adhere to testing recommendations when attending to women that reside in areas with high rates of syphilis. This low compliance with the CDC and ACOG guidelines on high-risk prenatal syphilis testing suggests that more providers education is needed.
Providers were more likely to test women with government-issued insurance, had a preterm delivery, resided in high-risk zip codes, and self-identified as Black. Similarly, Sheikh et al. (2008), found socioeconomic factors such as maternal residence, lack of healthcare insurance, and incarceration to be associated with lack of prenatal syphilis testing [9]. We found that those with government insurance such as Medicaid and Medicare were tested more frequently than women with commercial insurance, which is on par with the 85% testing rate among pregnant women found in a study using MarketScan data [25]. Government-funded health insurance afford women the opportunity to seek and receive care during pregnancy. Women who delivered preterm were also tested more often, possibly because of more frequent follow-up appointments associated with preterm risk. We were, however, unable to assess the reasons for preterm birth.
There were several limitations in this study. First, syphilis testing may have taken place in a lab not covered by the INPC, in which case a woman would appear not to be tested [13]. Additionally, results are dependent on institutions entering data correctly. Another limitation of this study is that we could not ascertain the stages of the syphilis diagnosis. Thus, it is possible that cases were from a previous infection that occurred before pregnancy that might not represent active syphilis. Additionally, the definition of high risk for this study did not encompass the entire definition of high risk as outlined by the CDC which includes individuals with risky sexual behavior, illicit drug use, STIs, or multiple sex partners during pregnancy [5]. Thus, it is possible for some women that were not classified as high risk based on the definition used in this study (high morbidity zip codes) to, in fact, be high risk. Lastly, assigned Logical Observation Identifiers Names and Codes (LOINC) coding to some laboratory tests was unclear as to which syphilis test was performed. Although all LOINCs with positive results were examined manually, it is still possible that misclassification could have occurred.