Syphilis in pregnancy and adverse birth outcomes: A nationwide longitudinal study in Brazil

The present study aimed to evaluate the association between syphilis in pregnancy and low birth weight, small for gestational age, and preterm birth.


| INTRODUC TI ON
Syphilis is a sexual infection caused by the Treponema pallidum. 1en acquired during pregnancy, transmission can occur from mother to children, leading to harmful effects on the unborn child including low birth weight, preterm delivery and stillbirth, which may be due to placental abnormalities and dysfunction caused by the inflammatory response to the disease. 2,3reening syphilis during prenatal care contributes to the adequate treatment of pregnant women with penicillin, reducing the impact of the disease on the fetus. 2 Untreated or inadequately treated maternal syphilis is associated with an increased risk of adverse pregnancy outcomes 3,4 including neonatal death (9%) and stillbirth (21%). 5The non-treponemal veneral disease research laboratory (VDRL) is the most common screening test used, which detects the antibodies released after infection.Also, its quantitative result (e.g., 1:2, 1:4, 1:64) is used to monitor the disease, as the VDRL titer decreases with the treatment, and a four-fold change means an adequate response to treatment. 2,6,7 Brazil, 16.9 cases of syphilis in pregnancy per 100 000 inhabitants were estimated in 2017, a 660% increase in 10 years 2,5 and it is similar to other countries in the world.Globally, 355 000 adverse birth outcomes were attributed to maternal syphilis. 5The Brazilian Ministry of Health recommends that all pregnant women should be tested for syphilis during the prenatal care, ideally in the first trimester.According to the Brazilian National Health Survey 80.1% of pregnant women also underwent the syphilis screening test during prenatal visits. 7,8st of the available studies that evaluate the laboratorial results for syphilis and adverse birth outcomes in middle and lowincome countries, such as Brazil, rely on small sample sizes or focus on specific regions of the country. 3,7us, considering the potential for improved pregnancy outcomes through the management of gestational syphilis, we hypothesized that untreated gestational syphilis and higher VDRL titers negatively impact on low birth weight, small for gestational age, and preterm birth.In this way, we aimed to estimate the association between syphilis in pregnancy and adverse outcomes at birth using a national population-based database.Additionally, we investigated the association according to non-treponemal titer and maternal treatment status and role of prenatal care.

| MATERIAL S AND ME THODS
This was a nationwide retrospective population-based cohort study that used the Brazilian National Information System for livebirths (SINASC) linked to the gestational syphilis cases from Notifiable Diseases Information System (SINAN) from 2011 to 2017.We included all pregnant women with and without syphilis registered with a singleton live birth and those with confirmed cases of congenital syphilis reported in the SINAN-syphilis records.

| Data source
In Brazil the Health Information System collects data following the regulation and organization of the Brazilian Health Systems (SUS).The information is primarily collected by health workers in individual level using standardized forms for notification in the healthcare settings.This information is under the Brazilian Ministry of Health, through the Department of Health Informatics of the SUS, and it is responsible for securely storing, preserving, and providing access to the databases. 9e SINASC has a 94.8% coverage of births in Brazil. 10The birth data is routinely collected using the declaration of live birth by the health worker who assisted with the delivery.The SINASC includes information from the mother (maternal age, maternal educational level), the pregnancy history (gestation length), and the newborn (birth weight, and newborn sex). 11e SINAN-Syphilis is a mandatory system for confirmed cases of gestational syphilis according to the Brazilian Ministry of Health criteria. 12It includes at the time of diagnosis the VDRL test result, treatment provided, clinical classification, socioeconomic and gestational information. 12

| Data linkage
The individual data was linked by the Cidacs-RL, an algorithm created at the Center of Data and Knowledge Integration for Health (CIDACS) which used common attributes of the databases, such as name, age or date of birth, mother's name, and municipality of residence.Details of the linkage process are available in other publications. 13,14e Research Ethics Committee of the Institute of Collective Health of the Federal University of Bahia (UFBA) approved the study protocol on December 8, 2020, and waived the informed consent as this study used electronic data without any personally identifiable information (CAAE: registration no.18022319.4.0000.5030).
The data governance in Brazil includes the Information Access Law (Law 12.527/2011), the Brazilian General Data Protection Law (Law 13.709/2018), and the National Health Council standards, Resolution 266 of December 2012, which establish principles and privacy protection measures, enabling administrative data use for research purposes.The data is available after ethical approval and authorization from the government. 9All process of data acquisition, linkage, storage, and de-identification process are performed by the CIDACS.

| Exclusion criteria
We excluded: (1) multiple births to avoid bias in the ascertainment of low birth weight cases, (2) births with <24 weeks or >43 weeks considering the international newborn size standards according to INTERGROWTH-21st, 15 (3) records confirmed as abortion or stillborn, (4) syphilis diagnosed prior to or after the gestational period, (5)   implausible birth weights, such as less than 500 g or equal or greater than 6500 g. 15 Details of these exclusions are shown in Figure 1.

| Study variables
[17] The exposures were: (1) the pregnant women with syphilis registered in SINAN-Syphilis or pregnant women not found in the gestational syphilis dataset but linked with a singleton live birth confirmed as congenital syphilis case; (2) the VDRL titer (≤8, 8-16, 16-32, 32-64, ≥64).For the complementary analyses, we combined the syphilis diagnosis with the treatment regimen prescribed categorized in pregnant without syphilis (reference), gestational syphilis treated (using penicillin G benzathine or other treatment), and gestational syphilis untreated.

| Statistical analyses
For descriptive analysis the variables studied were related to syphilis notification during pregnancy as follows: mother's year of education (≤3, 4-7, 8-11, ≥12 years), mother's race/skin color (categories according to the Brazilian Institute of Geography and Statistics: white, black, yellow, which will be referred to as Asian descent, parda, and indigenous), maternal marital status (with a partner, without a partner), number of prenatal visits (>6, ≤6), type of delivery (cesarean or The magnitude of the association between syphilis in pregnancy and adverse outcomes at birth was expressed as odds ratio (OR) with the respective confidence intervals (95% CI).It was considered the significance alpha level of 0.05.The covariates included in the adjustments were selected a priori based on the literature (mother's age, mother's marital status, mother's race/skin color, mother's educational level, region).A similar analytical procedure was done considering as variable of exposure the VDRL titer and treatment received.Also, the analyses were stratified by prenatal care, considering this variable as an effect modifier.

| RE SULTS
This study included 155 214 pregnant women with syphilis and 17 775 603 pregnant women without syphilis, giving an overall prevalence of 8.7/1000 live births.The characteristics of the population according to infection during pregnancy are described in Table 1.A total of 94 639 (60.97%) pregnant women with syphilis  (Figure 2; Table 5).In the analyses stratified by number of prenatal care appointments, regardless of VDRL titers, mothers with equal to or fewer than six prenatal appointments had higher odds for all adverse birth outcomes compared to those with more than six appointments (Table 7).
When pregnancy outcomes were analyzed regarding treatment status, infants born to untreated mothers with syphilis had a higher odds ratio for being underweight (aOR LBW 2.52, 95% CI:  8).

| DISCUSS ION
Using nationwide real-world data and integrating different sources from the Brazilian health information systems, we found higher chances of low birth weight, small for gestational age, and preterm birth for pregnant women with than those without gestational syphilis.It was observed an increased odds with increased maternal VDRL TA B L E 4 Association between gestational syphilis and birth outcomes stratified by prenatal care.titers, and higher chances among newborns from untreated women.
Furthermore, higher odds for all outcomes from mothers with equal or less than six prenatal appointments were observed.
Vertical transmission can occur at any time of pregnancy and clinical stage of syphilis.In this way, the higher the presence of the spirochetes in the blood circulation, the higher the risk of TA B L E 5 Association between gestational syphilis VDRL titer and birth outcomes.Abbreviations: CI, confidence interval; OR, odds ratio.
transmission. 18One mechanism by which syphilis during pregnancy can lead to these outcomes is T. pallidum sp.pallidum can spread to different organs of the fetus and cause damage to the placenta and umbilical cord, usually from the 16th gestational week. 3Thus, gestational syphilis involves an inflammatory response which can result in intrauterine growth restriction, stillbirth, or premature birth, compromising viability and fetal growth. 3e non-treponemal test VDRL is useful to investigate and monitor syphilis in pregnancy, since the titers show increased positivity with active syphilis and decreased post-treatment, with a two dilutions change being clinically relevant. 191][22] However, an association exists between the higher VDRL titers, which show an increased inflammatory response, and the consequent increase in the odds of low birth weight, small for gestational age, and preterm birth.
Consistent with our findings, previous studies regarding gestational syphilis on birth outcomes found that untreated pregnant women had an increased risk of low birth weight and preterm birth. 3,21,23In a retrospective study performed in the Southern region of Brazil, with a sample of 306 cases of syphilis in pregnancy, the prevalence ratio was 60% higher for low birth weight (PR 1.6, 95% CI: 1.14-2.28)and preterm birth (PR 1.6, 95% CI: 1.17-2.21). 21so, a systematic review and meta-analysis found that preterm birth and low birth weight were 5.8% more frequent among untreated maternal syphilis. 3Similarly, a study with Chinese pregnant women found for untreated mothers, 27% and 44% higher odds of preterm birth (aOR 1.27, 95% CI: 1.02-1.59)and low birth weight (aOR 1.44, 95% CI: 1.11-1.86),respectively, when compared to treated mothers. 23rly diagnosis and treatment play a crucial role in preventing congenital syphilis and other adverse pregnancy outcomes caused by maternal syphilis. 24,25Also, our findings suggest pregnant women with more than six prenatal consultations had lower odds of adverse birth outcomes compared to those who attended fewer visits, which corroborates with previous studies. 20,21e WHO recommends that all pregnant women infected with syphilis receive at least one dose of penicillin G benzathine in the first trimester. 24In this way, the Brazilian Ministry of Health recommends the penicillin treatment regime according to the disease stage and diagnosis time. 25 vaginal), Brazilian region (Southeast [SE], North [N], Northeast [NE], South [S], Center-West [CW]), maternal age (≤20, 20-35, ≥35), sex of the child (male or female); Apgar 1 (≥7, <7); Apgar 5 (≥7, <7).Initially, we performed a descriptive bivariate analysis, Pearson chi-squared test, with maternal sociodemographic and newborn characteristics according to syphilis infection (with/without syphilis).
The data were processed and analyzed with the software STATA version 15.1 (Stata Corporation, 153 College Station, USA).

F I G U R E 1
Study population flow diagram.TA B L E 1 Descriptive analysis of newborns and mother's characteristics.

women without syphilis Pregnant women with syphilis Low birth weight Small for gestational age Preterm birth Low birth weight Small for gestational age Preterm birth
Association between gestational syphilis and birth outcomes.
Association between gestational syphilis treatment and birth outcomes.Adjusted by mother's age, mother's marital status, mother's race/skin color, mother's educational level, region.
Note: Adjusted by mother's age, mother's marital status, mother's race/skin color, mother's educational level, region.Abbreviations: CI, confidence interval; OR, odds ratio; VDRL, veneral disease research laboratory.TA B L E 6

>6 visits ≤6 visits >6 visits ≤6 visits Treatment Categories OR crude (95% CI) P value OR crude (95% CI) P value OR adjusted (95% CI) P value OR adjusted (95% CI) P value
Association between gestational syphilis VDRL titer and birth outcomes stratified by prenatal care.Adjusted by mother's age, mother's marital status, mother's race/skin color, mother's educational level, region.Association between gestational syphilis treatment and birth outcomes stratified by prenatal care.Adjusted by mother's age, mother's marital status, mother's race/skin color, mother's educational level, region.Abbreviations: CI, confidence interval; OR, odds ratio.the data available.Information on how to apply to access the data can be found at https:// cidacs.bahia.fiocr uz.br/ en/ .
In Brazil, Primary Health Care is essential in coping with gestational syphilis since it is the main gateway to health services.The screening of gestational syphilis with VDRL test should occur during the first prenatal visit in the first trimester.In the case of syphilis seropositive, the treatment occurs at the primary health care without needing hospitalization.The lack of prenatalTA B L E 7Abbreviations: CI, confidence interval; OR, odds ratio; VDRL, veneral disease research laboratory.However, upon reasonable request and provided all ethical and legal requirements are met, the institutional data curation team can make TA B L E 8