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 Table of Contents  
Year : 2016  |  Volume : 33  |  Issue : 3  |  Page : 297-301

Bacterial vaginosis in spontaneous preterm and term birth: A case–control study

1 Department of Obstetrics and Gynecology, Mother and Child Hospital, Akure, Ondo State, Nigeria
2 Department of Obstetrics and Gynecology, University of Benin, Benin City, Edo State, Nigeria
3 Department of Obstetrics and Gynecology, Ekiti State University, Ado-Ekiti, Ekiti State, Nigeria
4 Department of Medical Microbiology, Ebonyi State University, Abakaliki, Ebonyi State, Nigeria

Date of Web Publication8-Feb-2017

Correspondence Address:
Adeniyi Kolade Aderoba
P.O. Box 603, Ondo Town, Ondo State 350001
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0189-5117.199820

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Background: Bacterial vaginosis (BV) is associated with adverse pregnancy outcomes, especially preterm birth (PTB). Unfortunately, there is a dearth of evidence on the link between BV and PTB occurring in sub-Saharan Africa to inform preventive interventions targeting BV associated with PTB.
Objectives: The objective of this study was to evaluate the association between genital tract colonization with BV and PTB.
Methods: In this prospective case–control study design, 82 women with spontaneous PTB (cases) or term birth (TB) (controls) were screened for BV. The diagnosis of BV was based on the Nugent scoring system. The association between BV and PTB was evaluated using multivariate logistic regression analysis.
Results: BV was significantly higher in women with PTB compared with those with TB (17 [41.5%] vs. 5 [12.2%]; P= 0.005). Furthermore, the odds of BV with PTB were higher among women who had PTB compared with TB after adjusting for a known factor, marital status, which differed significantly between women with preterm and TB (adjusted odds ratio 4.5, 95% confidence interval [1.4–14.4]).
Conclusion: Women with BV in pregnancy have increased odds of having PTB. Given the challenge of preterm labor and PTB, screening and treatment of women for BV early in pregnancy may be a veritable strategy to prevent PTB and its consequences.

Keywords: Bacterial vaginosis; Nigeria; pregnancy; preterm birth; term birth.

How to cite this article:
Aderoba AK, Olokor OE, Olagbuji BN, Ande AB, Okonkwo CA, Ojide CK. Bacterial vaginosis in spontaneous preterm and term birth: A case–control study. Trop J Obstet Gynaecol 2016;33:297-301

How to cite this URL:
Aderoba AK, Olokor OE, Olagbuji BN, Ande AB, Okonkwo CA, Ojide CK. Bacterial vaginosis in spontaneous preterm and term birth: A case–control study. Trop J Obstet Gynaecol [serial online] 2016 [cited 2023 Jun 1];33:297-301. Available from: https://www.tjogonline.com/text.asp?2016/33/3/297/199820

  Introduction Top

Globally, bacterial vaginosis (BV) is the most common lower genital tract infection in women of reproductive age;[1] with prevalence ranging from 4% to 64%.[2] In pregnancy, BV increases the risk for several adverse outcomes,[2] spontaneous preterm birth (PTB) in particular.[3],[4] The risk of neonatal morbidity and mortality after PTB, especially early PTB, is substantial.[5],[6] As an example, early PTB causes enduring neurologic disability from infancy to adulthood.[5],[6] Besides the cost of the associated neonatal intensive care, PTB poses a significant burden on the parents and families.[5]

Although several studies have described the prevalence of BV among pregnant women in Nigeria,[7],[8],[9],[10],[11] there is a paucity of data on the relationship between BV and PTB.[12],[13] To the best of our knowledge, the data comparing the occurrence of BV infection in women who had spontaneous PTB versus those who had spontaneous term birth (TB) in Nigeria are nonexistent. In light of the dearth of data on the relationship between BV, preterm, and TBs, there is a need for further research to explore this relationship among women in our setting to help the development of intervention strategies for preventing PTB and its associated risks.

  Methods Top

Study setting/design

From April 2010 to September 2010, we conducted an unmatched case–control study assessing BV infection in women who presented with spontaneous labor at the Obstetric Unit of the University of Benin Teaching Hospital (UBTH), Benin City, Nigeria. Ethical approval was obtained from the Ethics and Research Committee of UBTH.

Study participants

Cases were women who presented in established preterm labor from 28 weeks to 36 weeks and 6 days of gestation and delivered in the facility. Controls were women who presented in spontaneous active labor at ≥37 weeks and <42 weeks and delivered in the Obstetric Unit. We determined gestational age using the last menstrual period and this was validated using ultrasonography performed prior to 20 weeks of gestation. A woman was considered to be in active-phase labor or established preterm labor if the cervical dilatation was ≥4 cm. Because delivery was imminent following the onset of active-phase labor or established preterm labor, the case and control groups were referred to as “PTB” and “TB” groups, respectively, in the rest of this manuscript.

Women were eligible for inclusion into the study as cases or controls if they gave written informed consent to participate in the study, had a singleton gestation, and had adequate prenatal care. Adequate prenatal care was defined as at least three antenatal visits documented in the prenatal record. Exclusion criteria were cervical dilatation ≥7 cm, risk factors for preterm labor such as cervical incompetence, previous history of preterm labor, febrile illnesses and polyhydramnios as well as medical or obstetric emergencies, including severe cardiopulmonary disease, preeclampsia/eclampsia, and antepartum hemorrhage. In addition, women who had vaginal douching or used antibiotics within 30 days prior to the onset of spontaneous active-phase labor or established preterm labor were also excluded from the study.

Sample size determination

Considering the prevalence rate of 11.5% and an approximate 6-fold risk (relative risk: 5.73) for developing PTB following genital tract infection with BV in a prior study,[14] it was calculated that a total sample of 62 women, 31 per group, would provide an 80% power and 95% confidence interval [CI]. The sample size was increased to 41 in each group to increase the accuracy of the study.


With the aid of a Cusco's speculum, a sample of the secretions from the posterior vaginal fornix was obtained from every eligible participant. The samples were smeared on glass slides and air-dried. After that, the smears were heat fixed, Gram stained, and oil immersion microscopy was performed on each smeared slide at ×1000 magnification. Bacterial morphotypes were assessed by the 10-point score described by Nugent et al.[15] and validated for use in pregnancy by Hillier et al.[16] To avoid bias with respect to the assessment of bacterial morphotypes, laboratory professionals were kept blinded to the grouping of participants. Only the study numbers were used as identifiers on the glass slides.

Data management and statistical analysis

The demographic and clinical characteristics of the study participants recorded were age, parity, level of education, marital status, gestational age at birth, and the presence or absence of BV in the genital tract. Statistical analysis was performed using SPSS software version 21.0 (SPSS Inc., Chicago, IL, USA). Categorical variables were compared with Pearson's Chi-square test or Fisher's exact test as appropriate. Continuous variables were compared with Student's t-test. Comparison was made between PTB and TB groups concerning exposure to genital tract colonization with BV, and multivariate logistic regression analysis was used to adjust for the impact of any potential confounder. The association between BV and the type of birth (PTB or TB) was determined using multivariate logistic regression. A probability level of ≤0.05 was considered statistically significant.

  Results Top

Overall, 82 women were included in the PTB and TB groups. Each group consisted of 41 women. BV was diagnosed in 17 (41.5%) and 5 (12.2%) women with PTB and TB, respectively (P = 0.005). The mean age of women in both groups was 29.5 years [Table 1]. Both groups were comparable with respect to mean maternal age (29.2 vs. 29.7 years; P = 0.61). Moreover, both groups did not differ significantly by parity and level of education [Table 1]. The women in the PTB group were more likely to be unmarried (22.0% vs. 2.4%, P = 0.014).
Table 1: Sociodemographic characteristics of the study population

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[Table 2] shows the clinical characteristics of the study population. The mean gestational age at birth among women with PTB was significantly lower than those with TB (33.2 ± 1.8 weeks vs. 39.0 ± 1.3 weeks; P < 0.001). Genital tract colonization with BV was significantly higher in women with PTB in comparison to those with TB (17 [41.5%] vs. 5 [12.2%], P = 0.003). This difference was statistically significant (crude odds ratio [OR]: 5.1, 95% CI [1.7–15.7]). Following adjustment for marital status which differed significantly between the case and the control groups, the relationship between genital tract colonization with BV and PTB remained significant (adjusted OR: 4.5, 95% CI [1.4–14.4]).
Table 2: Clinical characteristics of the study population

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Boxplot in [Figure 1] shows the relationship between Nugent score and gestational age at birth in clusters of women with PTB and TB.
Figure 1: Boxplot showing relationship between Nugent score and gestational age at birth in clusters of women with preterm and term birth with whiskers from minimum to maximum

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  Discussion Top

We found that the proportion of genital tract colonization with BV was higher among women with PTB compared with women who had TB. The odds of BV were higher among women who had PTB compared with women who did not. Furthermore, after adjusting for a known factor, marital status, which was found to be significantly different between women with preterm and TB, the odds of BV remained significantly higher in women with PTB. The clinical implications of our study findings would be that BV infection could contribute significantly to the occurrence of PTB. Furthermore, adverse infant outcomes related to PTB could be prevented or minimized by the early identification and treatment of women with BV infection.

Our results were similar to the published findings from studies conducted within and outside Nigeria.[3],[4],[13],[14],[17],[18],[19] Afolabi et al. prospectively studied 246 consecutive pregnant women who had examination of vaginal smears for BV using “Nugent scoring system between 14 and 36 weeks” gestation in a single institution in Nigeria and found a 2-fold increased risk of PTB with BV infection.[13] In a case–control study of 160 women in labor at a single health facility in Iran, Nejad and Shafaie, using “Amstel scoring system,” found a higher proportion of women with BV in the preterm labor group compared with the term labor group (25% vs. 11.3%, P = 0.039).[3] Likewise, in a cohort study of women at 16–28 weeks of gestation in India, Purwar et al. found an association between BV infection and PTB.[14] Similar to the Afolabi et al.'s study,[13] Purwar et al.[14] also found an increased risk of BV infection with premature rupture of membranes, which by itself is associated with an increased risk of preterm labor and birth. In contrast to our study, Thorsen et al. screened Danish women for BV and found no increased risk of spontaneous PTB with BV.[20] This dissimilar observation could be the result of differences in the study population and diagnostic technique for BV. Thorsen et al. screened women using Amstel's clinical criteria and enrolled participants at <24 weeks' gestation, in contrast to this study.

The strengths of our study include the method employed in diagnosing BV. The use of Nugent scoring system to diagnose BV in this study allows for the correct identification of bacterial morphotypes in abnormal vaginal flora. Compared to other diagnostic scoring systems for BV, Nugent scoring system has greater reproducibility and sensitivity, and it is the gold standard diagnostic scoring system for BV.[2],[15]

Another important strong point for this research is the adjustment of the effect of potential confounding variables which differed significantly between women with PTB and TB. As the maternal characteristics of preterm and TB groups were compared, we were able to identify and control the confounding effect of marital status which was significantly different between both groups. However, this study may have been limited by the relatively small sample size.

  Conclusion Top

Our data suggest that women with BV in pregnancy are at an increased risk of PTB. Given the challenge of preterm labor and PTB, screening and treatment of women for BV early in pregnancy may be a veritable strategy to prevent PTB and its consequences.


The authors appreciate the staff of the Departments of Obstetrics and Gynaecology and Medical Microbiology of UBTH for supporting the researchers with logistics during the study.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Morris M, Nicoll A, Simms I, Wilson J, Catchpole M. Bacterial vaginosis: A public health review. BJOG 2001;108:439-50.  Back to cited text no. 1
Denney JM, Culhane JF. Bacterial vaginosis: A problematic infection from both a perinatal and neonatal perspective. Semin Fetal Neonatal Med 2009;14:200-3.  Back to cited text no. 2
Nejad VM, Shafaie S. The association of bacterial vaginosis and preterm labor. J Pak Med Assoc 2008;58:104-6.  Back to cited text no. 3
Leitich H, Kiss H. Asymptomatic bacterial vaginosis and intermediate flora as risk factors for adverse pregnancy outcome. Best Pract Res Clin Obstet Gynaecol 2007;21:375-90.  Back to cited text no. 4
Blencowe H, Cousens S, Chou D, Oestergaard M, Say L, Moller AB, et al. Born too soon: The global epidemiology of 15 million preterm births. Reprod Health 2013;10 Suppl 1:S2.  Back to cited text no. 5
Vogel JP, Lee AC, Souza JP. Maternal morbidity and preterm birth in 22 low- and middle-income countries: A secondary analysis of the WHO Global Survey dataset. BMC Pregnancy Childbirth 2014;14:56.  Back to cited text no. 6
Sunday-Adeoye I, Ogbonaya LU, Ugwu J, Obinna JA. Bacteria vaginosis in antenatal patients in Abakaliki, Nigeria. Trop J Obstet Gynaecol 2006;23:100-3.  Back to cited text no. 7
Ibrahim SM, Bukar M, Galadima GB, Audu BM, Ibrahim HA. Prevalence of bacterial vaginosis in pregnant women in Maiduguri, North-Eastern Nigeria. Niger J Clin Pract 2014;17:154-8.  Back to cited text no. 8
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Lar-Ndam N, Yohanna S, Madaki JK. The prevalence of bacterial vaginosis amongst pregnant women attending antenatal care at ECWA Evangel Hospital, Jos, Nigeria. Niger J Fam Pract 2013;3:19-24.  Back to cited text no. 9
Awoniyi AO, Komolafe OJ, Bifarin O, Olaniran O. Bacterial vaginosis among pregnant women attending a primary health center in Ile-Ife, Nigeria. Glob Adv Res J Med Med Sci 2015;4:57-60.  Back to cited text no. 10
Ajani G, Oduyebo O, Haruna M, Elikwu C. Nugent scores for pregnant women in a tertiary institution in Nigeria. Adv Microbiol 2012;2:531-6.  Back to cited text no. 11
Adesiji YO, Taiwo SS, Adekanle DA, Oboro VO, Fayemiwo SA, Opaleye OO. Bacterial vaginosis and pregnancy outcome in Osogbo, Nigeria. Res J Med Sci 2007;4:195-8.  Back to cited text no. 12
Afolabi BB, Moses OE, Oduyebo OO. Bacterial vaginosis and pregnancy outcome in Lagos, Nigeria. Open Forum Infect Dis 2016;3:ofw030.  Back to cited text no. 13
Purwar M, Ughade S, Bhagat B, Agarwal V, Kulkarni H. Bacterial vaginosis in early pregnancy and adverse pregnancy outcome. J Obstet Gynaecol Res 2001;27:175-81.  Back to cited text no. 14
Nugent RP, Krohn MA, Hillier SL. Reliability of diagnosing bacterial vaginosis is improved by a standardized method of gram stain interpretation. J Clin Microbiol 1991;29:297-301.  Back to cited text no. 15
Hillier SL, Krohn MA, Nugent RP, Gibbs RS. Characteristics of three vaginal flora patterns assessed by gram stain among pregnant women. Vaginal infections and prematurity study group. Am J Obstet Gynecol 1992;166:938-44.  Back to cited text no. 16
Allsworth JE, Peipert JF. Prevalence of bacterial vaginosis: 2001-2004 National Health and Nutrition Examination Survey data. Obstet Gynecol 2007;109:114-20.  Back to cited text no. 17
Nelson DB, Bellamy S, Clothier BA, Macones GA, Nachamkin I, Ruffin A, et al. Characteristics and pregnancy outcomes of pregnant women asymptomatic for bacterial vaginosis. Matern Child Health J 2008;12:216-22.  Back to cited text no. 18
Eschenbach DA, Gravett MG, Chen KC, Hoyme UB, Holmes KK. Bacterial vaginosis during pregnancy. An association with prematurity and postpartum complications. Scand J Urol Nephrol Suppl 1984;86:213-22.  Back to cited text no. 19
Thorsen P, Vogel I, Olsen J, Jeune B, Westergaard JG, Jacobsson B, et al. Bacterial vaginosis in early pregnancy is associated with low birth weight and small for gestational age, but not with spontaneous preterm birth: A population-based study on Danish women. J Matern Fetal Neonatal Med 2006;19:1-7.  Back to cited text no. 20


  [Figure 1]

  [Table 1], [Table 2]

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