Objective
The objective of the study was to estimate the rates of testing, prevalence, and follow-up testing for chlamydial and gonococcal infection in a nationally based population that is comparable with the US pregnant population in terms of age and race.
Study Design
We extracted laboratory results for 1,293,423 pregnant women tested over a 3-year period.
Results
During pregnancy, 59% (761,315 of 1,293,423) and 57% (730,796 of 1,293,423) of women were tested at least once for Chlamydia trachomatis or for Neisseria gonorrhoeae , respectively. Of those women tested, 3.5% (26,437 of 761,315) and 0.6% (4605 of 730,796) tested positive for chlamydial and gonococcal infection, respectively, at least once during pregnancy. Of those women who were initially positive for the given infection, 78% (16,039 of 20,489) and 76% (2610 of 3435) were retested, of whom 6.0% (969 of 16,039) and 3.8% (100 of 2610) were positive on their last prenatal test for C trachomatis and N gonorrhoeae , respectively.
Conclusion
Many pregnant women are not tested for C trachomatis and N gonorrhoeae despite recommendations to test. Follow-up testing to monitor the effectiveness of treatment is also not always performed.
Chlamydia trachomatis (from the Greek word χλαμúδα meaning cloak) is a sexually transmitted infection that affects an estimated 100,000 pregnant women in the United States annually. Neisseria gonorrhoeae affects approximately 13,200 pregnant women annually. Left untreated, these infections have been associated with a number of adverse maternal outcomes, such as early onset of labor, premature rupture of membranes, and uterine infection after delivery. These infections can also be transmitted from mother to newborn during delivery, resulting in potentially serious consequences for the infant, including ophthalmia neonatorum, chlamydial pneumonitis, and disseminated gonococcal infection.
Guidelines for testing for these infections in pregnant women vary. According to the current Centers for Disease Control and Prevention (CDC) guidelines, all pregnant women should be routinely screened for C trachomatis at the first prenatal visit, and those considered to be at risk or who live in an area in which the prevalence is high should also be screened for N gonorrhoeae . Women who test positive for C trachomatis should be retested 3 weeks after the completion of therapy to ensure therapeutic cure, whereas those positive for N gonorrhoeae do not require a test of cure.
Repeat screening for C trachomatis is recommended during the third trimester for all women 25 years of age or younger and those at increased risk and within 3-6 months for those women discovered to be infected during the first trimester. The guidelines for retesting for gonococcal infections are similar, with women younger than 25 years of age considered to be at highest risk. The screening guidelines vary somewhat by organization and were in flux during the study period. For example, the American College of Obstetricians and Gynecologists (ACOG) did not recommend universal screening for C trachomatis until 2007.
To assess compliance with these recommendations and determine the prevalence of these infections, we examined testing patterns for C trachomatis and N gonorrhoeae among nearly 1.3 million pregnant women who are nationally representative of the pregnant population.
Materials and Methods
Quest Diagnostics has more than 145 million patient encounters each year across the United States. The test results are stored in the Quest Diagnostics Informatics Data Warehouse, which is the largest private clinical laboratory data warehouse in the country. For this study, we extracted testing data for pregnant women as described below; all the data were deidentified prior to analysis. This study was determined to be exempt by the Western Institutional Review Board.
A woman aged 16-40 years was determined to be pregnant if she had a rubella antibody test performed as part of a standard obstetric panel (Current Procedural Terminology code 80055) during our 36 month study period (June 1, 2005, through May 30, 2008). Women were included in the study only if they had any other laboratory test performed at Quest Diagnostics during what was estimated to be the third trimester to ensure continuity in laboratory services and to exclude women whose pregnancies ended prior to the third trimester. Of the women in this study, 9358 (0.7%) had subsequent pregnancies during the study period. Only data from the first pregnancy is considered in the analysis.
Patient demographic data were collected to assess the comparability of our study population with that of pregnant women in the United States. Information about the race group of the pregnant women, as identified by the ordering physician, was recorded when it was available from the subset of women who had a maternal serum screen performed at Quest Diagnostics. Data on race group were not available for California residents (which represented approximately 16% of the study population) because the California Department of Public Health performs maternal serum screening tests. This information was used to compare the race group distribution of the pregnant study population to that of the pregnant population in the United States (with and without California) during 2006. As a marker of socioeconomic status, we also compared the proportion of women in the study population who were Medicaid recipients with that of the US Medicaid population in 2007.
Chlamydial and gonococcal testing results from the study population were extracted from the Informatics Data Warehouse. C trachomatis and N gonorrhoeae infections were identified using one of the following tests: (1) strand displacement amplification (Beckman Dickinson and Co, Franklin Lakes, NJ) (approximately 70% of test volume); (2) deoxyribonucleic acid hybridization with chemiluminescent detection (Gen-Probe Inc, San Diego, CA) (approximately 20%); and (3) target capture, transcription-mediated amplification, dual-kinetic assay (Gen-Probe) (approximately 10%).
Overall chlamydial and gonococcal testing rates were calculated as the number of pregnant women who were tested at any time during pregnancy divided by the total number of pregnant women in the study. The overall prevalence rates were calculated as the number of pregnant women who tested positive for C trachomatis or N gonorrhoeae at least once during pregnancy divided by the number of women tested. The age-adjusted rates were calculated using the following age categories: 16-19 years, 20-24 years, 25-29 years, 30-34 years, and 35-40 years.
In addition, we estimated the number of women who were tested during their first prenatal visit for C trachomatis (as is recommended by most guidelines) or for N gonorrhoeae . A chlamydial or gonococcal test was considered to be performed during the first prenatal visit if it occurred shortly before or during the visit when the obstetric panel–based rubella test was performed.
Finally, we assessed adherence with the recommendations for repeat testing and examined follow-up testing patterns (in terms of test frequencies and results) for all study participants.
Statistical comparisons were made using the Pearson χ 2 test to assess differences between proportions, and a multivariate logistic regression was performed to determine the independent associations of race and age with these binary outcomes. Our multivariate logistic model included only those patients with a maternal serum screen result. SAS 9.2 (SAS Institute Inc, Cary, NC) was used for all data analyses.
Results
Comparability of study population to US pregnant population
We included 1,293,423 pregnant women aged 16-40 years in the study population. Of these women, 525,258 (41%) had a maternal serum screen test result in the Informatics Data Warehouse. Comparison of the race group distribution of women in the study population with that of all US pregnancies outside California during 2006 indicated a difference of less than 3% for each race group ( Table 1 ). Similarly, the age distribution of women in our study was similar to that of all pregnant women in the United States ( Table 1 ), although women younger than 25 years old were relatively underrepresented and women older than 30 years were relatively overrepresented in our study population. As a result, we also report below testing and positivity rates for chlamydial and gonococcal infections that are directly adjusted to the national age distribution. Within our study population, 18.1% were identified as having Medicaid coverage, compared with 18.7% in the US population with Medicaid coverage.
| Group | Percent of total study population (n) | Percent of total US pregnant population minus California (n) | Percent of total US pregnant population (n) |
|---|---|---|---|
| Race group a | |||
| African American | 14.9 (78,192) | 15.7 (569,689) | 14.4 (600,846) |
| Asian | 5.8 (30,260) | 4.2 (153,699) | 5.3 (222,235) |
| White | 56.1 (294,410) | 58.2 (2,106,584) | 54.2 (2,259,262) |
| Hispanic | 18.9 (99,448) | 20.1 (729,666) | 24.4 (1,016,397) |
| Other | 4.4 (22,948) | 1.8 (63,297) | 1.7 (70,683) |
| Total | 100.0 (525,258) | 100.0 (3,622,935) | 100.0 (4,169,423) |
| Age group, y | |||
| 16-19 | 8.2 (105,619) | N/A | 10.0 (417,033) |
| 20-24 | 20.3 (262,931) | N/A | 25.9 (1,080,437) |
| 25-29 | 29.1 (376,847) | N/A | 28.3 (1,181,899) |
| 30-34 | 27.0 (349,570) | N/A | 22.8 (950,258) |
| 35-40 | 15.3 (198,456) | N/A | 13.0 (539,796) |
| Total | 100.0 (1,293,423) | N/A | 100.0 (4,169,423) |
a In the study population, only those with a maternal serum screen test were used in the race group comparisons.
Testing for chlamydial and gonococcal infection
Figure 1 highlights the major results of our investigation. During pregnancy, 761,315 (59%) of the 1,293,423 women were tested for C trachomatis and 730,796 (57%) were tested for N gonorrhoeae at least once (the age-adjusted rates were 60% and 58%, respectively). Testing for these pathogens was usually performed concurrently because 95% of the women who were tested for chlamydial infection were also tested for gonococcal infection at the same time. Testing rates decreased steadily as maternal age increased ( Figure 2 ). African American women had the highest chlamydial (74%) and gonococcal (70%) testing rates. White women had the lowest chlamydial (59%) and gonococcal (56%) testing rates ( Table 2 ).
| Testing rates, % | Positivity rates, % | OR for CT testing rates (95% CI) | OR for NG testing rates (95% CI) | OR for CT positivity rates (95% CI) | OR for NG positivity rates (95% CI) | |||
|---|---|---|---|---|---|---|---|---|
| Race group | C trachomatis a | N gonorrhoeae b | C trachomatis d | N gonorrhoeae e | ||||
| African Americans, n c | 74.0 (78,213) | 70.4 (78,213) | 10.7 (57,850) | 2.8 (55,033) | 1.000 | 1.000 | 1.000 | 1.000 |
| Asians, n c | 63.2 (30,257) | 56.5 (30,257) | 2.4 (19,125) | 0.4 (17,044) | 0.916 (0.889–0.943) | 0.811 (0.788–0.835) | 0.463 (0.418–0.512) | 0.321 (0.249–0.412) |
| Whites, n c | 59.2 (294,432) | 56.3 (294,432) | 2.1 (174,190) | 0.4 (166,380) | 0.765 (0.752–0.778) | 0.786 (0.773–0.799) | 0.320 (0.306–0.334) | 0.210 (0.191–0.232) |
| Hispanics, n c | 62.7 (99,434) | 60.1 (99,434) | 4.2 (62,362) | 0.5 (59,753) | 0.787 (0.771–0.803) | 0.818 (0.803–0.835) | 0.501 (0.477–0.526) | 0.243 (0.215–0.276) |
| Others, n c | 60.9 (22,934) | 57.2 (22,934) | 2.8 (13,955) | 0.4 (13,127) | ||||
| Race missing, n c | 56.5 (768,153) | 54.6 (768,153) | 3.0 (433,833) | 0.5 (419,459) | ||||
| Total, n f | 58.9 (1,293,423) | 56.5 (1,293,423) | 3.5 (761,315) | 0.6 (730,796) | ||||
| Age group, y | ||||||||
| 16-24 | 71.5 (368,550) | 69.2 (368,550) | 6.6 (263,422) | 1.3 (255,256) | 1.000 | 1.000 | 1.000 | 1.000 |
| 25-29 | 64.0 (376,847) | 61.5 (376,847) | 1.7 (241,048) | 0.3 (231,803) | 0.858 (0.847–0.870) | 0.852 (0.841–0.864) | 0.266 (0.254–0.278) | 0.270 (0.242–0.301) |
| 30-34 | 60.2 (349,570) | 57.8 (349,570) | 0.7 (210,589) | 0.1 (202,124) | 0.787 (0.775–0.799) | 0.779 (0.767–0.791) | 0.114 (0.105–0.124) | 0.120 (0.098–0.147) |
| 35-40 | 58.5 (198,456) | 56.0 (198,456) | 0.4 (116,094) | 0.1 (111,134) | 0.758 (0.733–0.784) | 0.741 (0.717–0.767) | 0.105 (0.081–0.135) | 0.124 (0.070–0.234) |
a Testing rates differed significantly across ethnicities: χ 2 = 5806.8; P < .001;
b Testing rates differed significantly across ethnicities: χ 2 = 5092.2; P < .001;
c Number of pregnant women eligible for testing in each race group;
d Positivity rates differed significantly across ethnicities: χ 2 = 8330.5; P < .001;
e Positivity rates differed significantly across ethnicities: χ 2 = 3143.0; P < .001;
f Total includes those whose race was not clearly specified in our database.
Multivariate logistic regression analysis to simultaneously examine the adjusted effects of age and race group provided the odds or likelihood of 1 group of pregnant women being tested compared with another group. Compared with women aged 16-24 years, women aged 35-40 years had approximately 32% lower adjusted odds (ie, lower likelihood) of being tested for C trachomatis . Likewise, compared with women aged 16-24 years, the odds of being tested for N gonorrhoeae in women aged 35-40 years were approximately 35% lower. The odds of being tested for C trachomatis in white women were 31% lower than in African American women; the odds of being tested for N gonorrhoeae in white women were 27% lower than in African American women ( Table 2 ).
Of the 1,293,423 women in our study population, 483,845 (37%) were tested for C trachomatis during their first prenatal visit, in accordance with current guidelines from the CDC and ACOG. The United States Preventative Services Task Force (USPSTF) recommends that pregnant women in a high-risk age group (aged 16-24 years) be tested for C trachomatis during the first prenatal visit. Of the 368,550 pregnant women aged 16-24 years, 143,019 (39%) were tested for chlamydial infection during the first prenatal visit. Likewise, of the 368,550 pregnant women aged 16-24 years in our study population, 137,612 (37%) were tested for gonococcal infection during the first prenatal visit in accordance with current CDC and USPSTF guidelines.
Prevalence of chlamydial and gonococcal infection
Of the 761,315 women who were tested for C trachomatis , 26,437 (3.5%) were positive at least once during pregnancy. Of the 730,796 women who were tested for N gonorrhoeae , 4605 (0.6%) were positive at least once during pregnancy. The age-adjusted rates were 4.6% and 0.8%, respectively. African American women were more likely to test positive for each infection than any other race group ( Table 2 ). The prevalence of C trachomatis and N gonorrhoeae infection was highest in the youngest study participants and decreased with increased maternal age ( Figure 3 ). For example, almost 16% of 16 year olds were positive for chlamydial infection; the positivity rate declined with age in almost linear fashion for the next 10 years and did not fall below 3% until the 26 year old age group.
Multivariate logistic regression analysis revealed that after considering both race and age, women 35-40 years of age had 9.5 times lower odds to test positive for C trachomatis than women 16-24 years of age; the odds of testing positive for N gonorrhoeae in women aged 35-40 years of age were more than 8 times lower than in women 16-24 years of age. The odds of testing positive for C trachomatis in white women were 3 times lower than in African American women; the odds of testing positive for N gonorrhoeae were 5 times lower than in African American women ( Table 2 ). Because testing positive for N gonorrhoeae is relatively rare, the odds ratio is a good approximation of the relative risk.
Follow-up testing and prevalence rates
To evaluate the value of repeat testing, we examined the results of follow-up testing in women who initially tested positive or negative for C trachomatis or N gonorrhoeae infection ( Table 3 ). Of the 20,489 pregnant women who were initially positive for C trachomatis , 16,039 (78%) were retested at least once in accordance with CDC guidelines. Of those who were retested, 18% (2885 of 16,039) had at least 1 subsequent positive result, and 6.0% (969 of 16,039) were still positive on their last prenatal test for chlamydial infection. Of the women who were initially positive for C trachomatis , 6755 (33.0%) had a test of cure performed within 6 weeks after a positive and 15% were positive on this first follow-up test.
| Variable | Number of pregnant women with initial positive result | One or more follow-up tests | One follow-up test only | Two follow-up tests only | Three follow-up tests only | Four or more follow-up tests |
|---|---|---|---|---|---|---|
| C trachomatis | 20,489 | |||||
| Number of women (%) with follow-up tests | 16,039 (78.3) | 9428 (46.0) | 4763 (23.2) | 1438 (7.0) | 410 (2.0) | |
| Number of positive results (%) on final test | 969 (6.0) | 517 (5.5) | 296 (6.2) | 105 (7.3) | 51 (12.4) | |
| N gonorrhoeae | 3453 | |||||
| Number of women (%) with follow-up tests | 2610 (75.6) | 1485 (43.0) | 820 (23.7) | 216 (6.3) | 89 (2.6) | |
| Number of positive results (%) on final test | 100 (3.8) | 39 (2.6) | 26 (3.2) | 6 (2.8) | 29 (32.6) |
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