Sima Gity, MD

Several studies have been conducted about Bacterial Vaginosis  and its relation with preterm labor that was accompanied with controversial results.  The aim of this study was to compare the frequency of Bacterial Vaginosis and common  genitourinary infections between term and pre-term pregnancies.


 In a case-control study, 249 pregnant women admitted to  Shohadyae Tajrish Hospital in 2004-2006 were studied. The cases (n=125) were chosen from  pregnant women with pre-term labor and the controls (n=124) were chosen from women  who had term labor.

All the patients underwent Bacterial Vaginosis investigation (Amsel  criteria) and group B streptococcus, Trichomonas, Candida Albicans and E.coli  with smear and culture (from cervix).


 Bacterial Vaginosis was significantly higher in patients with  rupture of membranes compared with patients with intact membranes (64.29% vs.  35.71%). The means of age, number of pregnancies, deliveries, living children, history of  abortion, infection with B streptococcus, Trichomonas, Gardnerella vaginalis, and Candida  Albicans showed no significant difference between two groups and only infection  with E.coli in the pre-term group was significantly higher (11.20% vs. 1.61%). Also history  of preterm labor (16.98% vs. 6.42%) and rupture of membranes (40% vs. 12.38%) was  significantly higher in preterm group.

 
 No significant relation was found between Bacterial Vaginosis  and preterm labor, only infection with E.coli was significantly higher in the  pre-term group in comparison with term pregnancies.


 There are several factors which predispose to preterm delivery.  It seems that activation of hypothalamus-pituitary-adrenal axis of mother or  the fetus, decidual hemorrhage, pathologic uterine distension and infection are  influencing factors (1). Epidemiologic studies have shown that stress and infection of  maternal genitourinary system independently and significantly increase the risk of  preterm labor (2).

Theoretically, pathogenic organisms ascend via lower genital  organs to uterine and may cause fetal membrane inflammation which leads to preterm  rupture of membranes and labor (3). Maternal genitourinary infection can initiate the  process of labor and cause preterm labor via different mechanisms including  activation of cytokine cycle and acceleration of labor process. Vaginal infection or colonization  increases the risk of fetal membrane infection and inflammatory cytokines affect the process  of labor (4). Different studies have suggested a wide range of microorganisms  including group B streptococcus, Trichomonas, Nisceria Gonorrhea, E.coli,  Bacterial Vaginosis, and Candida Albicans as the predisposing factors of preterm labor  (5-7). Various studies about Bacterial Vaginosis have ended up in controversial  results. There have been several studies showing a significant relationship between  Bacterial Vaginosis and preterm labor (8-13) while some other studies have denied this  relationship (14-18) and even some of them have indicated a reverse relationship (19,  20). Moreover, the prevalence of Bacterial Vaginosis are widely different in  vaginal smears of asymptomatic women in different countries (21). Therefore, the  prevalence of Bacterial Vaginosis and its relationship with preterm labor has to be  separately investigated in each nation (14).

The purpose of this study was to evaluate the prevalence of  Bacterial Vaginosis and other common vaginal infections in pregnant women with term or  preterm labor in Shohada Tajrish Hospital from 2005 to 2007. Our study included  249 patients in two groups of term (124 patients) and preterm (125 patients) labor.

We enrolled 249 patients who referred to Shohada Tajrish  Hospital from 2005 to 2007 for delivery in a case-control study after approval of  ethics committee of Research Deputy of Shahid Beheshti University of Medical Sciences. The  cases included 125 women who experienced preterm labor and the controls were 124  women with term delivery.

After obtaining the data related to demographic variables by a  questionnaire, the patients underwent microbiological studies to evaluate infection  or colonization with Bacterial Vaginosis (KOH smear and wet smear for clue cells and  PH evaluation by Amsel method), Group B Streptococcus (Blood Agar media),  Trichomonas (vaginal wet smear), Candida Albicans (visualizing hyphae after adding KOH to  simple smear) and E.Coli (EMB media). The smear and culture samples were taken  from the cervix with a sterilized swab prior to the first vaginal examination by the  chief resident or the senior residents in charge in the primary visit. The samples of the  cultures were taken immediately to the laboratory of the hospital to be cultured in  the mentioned media. The smears were all reported by the chief resident and the  results of the cultures were confirmed by the Pathology Department of the hospital.

The data was analyzed by t-test, chi-square or Fischer’s exact  test in SPSS ver. 12.0. P values below 0.05 were assumed significant.


 There were no significant differences in the mean age, number of  previous pregnancies, deliveries and live births, and also in the history  of abortion between two groups. However, history of preterm labor (16.98% vs. 6.42%) and  rupture of membranes (40% vs. 12.38%) were significantly higher in patients  with preterm labor (

). Although no difference was found between the prevalence of  Bacterial Vaginosis, group B streptococcus, Trichomonas and Candida Albicans among  two groups, our results revealed that only E. coli infection was significantly  higher in cases than controls (11.20% vs. 1.61%), (

). Our study indicated that the frequency of Bacterial Vaginosis  was significantly higher (64.29% vs. 35.71% with P=0.001) in patients with  ruptured membranes in comparison with patients with intact membranes (


 A lot of studies have shown a significant relationship between  Bacterial Vaginosis and preterm labor. For example, Azargoon  

 (8) have demonstrated the significant relationship of Bacterial Vaginosis in gestational weeks of  16-36 with preterm labor and rupture of the membranes. Other studies have verified this  relationship (9-13) and reported relative risks of 1.1 (9) to 1.86 (10). However, there  have been other studies overruling this correlation (14-18). Furthermore, Oakeshott 

.  (19) showed a significant reverse relationship between Bacterial Vaginosis and  preterm labor. Our results also revealed no significant relationship between  Bacterial Vaginosis and other genitourinary infections like group B streptococcus,  Trichomonas, and Candida Albicans in two groups of term and preterm labor.

This diversity of results might be caused by different factors.  One of the most important one can be the effects of confounding factors, though  our results reveal no significant difference in mean ages of mothers, and frequency of  gravity, parity, history of abortion and the number of living children in 2 groups. It  has been shown in a study that occurrence of Bacterial Vaginosis in earlier weeks of  pregnancy was associated with a higher rate of preterm labor (9). A meta-analysis has  also showed that Bacterial Vaginosis in early stages of pregnancy is an important risk  factor of preterm delivery and spontaneous abortion (22). We also should consider the role  of microorganisms that cannot be cultured in routine media and detected by routine  testing. For example, it has been shown that colonization of cervix with Ureaplasma  Urealyticum is related with preterm deliveries (23, 24) and its relative risk can be as high  as 3.34 (23). It has also been indicated that anaerobes are the most common etiologic  factor of Bacterial Vaginosis and have the highest prevalence in women experiencing  preterm labor (25). But these bacteria could not be evaluated in our study and a lot  of other studies. Some other studies mention organism load as a predictive factor of  preterm labor (14,26,27). Of note, higher organism load can cause a more severe  inflammation that can more intensely affect the course of the pregnancy and delivery. This  variable could not be evaluated in our study either.

Moreover, the prevalence of Bacterial Vaginosis has shown to be  widely different in different countries (21) and this warrants an individual study  to evaluate the prevalence of Bacterial Vaginosis and its relationship with preterm labor  in each nation (14).

It has also been shown that preterm labor is a possibility in  any pregnant woman who under goes stress or infection. There are many unknown factors  influencing this process and the endocrine and immune systems of pregnant women are  involved (2, 29). Thus, even though we have applied the greatest possible effort to  diminish the role of confounding factors, they cannot be totally eliminated. For  example, the rates of membrane rupture (40% vs. 12.38% with P=0.009) and history of  preterm labor (16.98% vs. 6.42% with P=0.016) were significantly higher in our  cases in comparison with our controls.

Our results even become more remarkable in comparison with  previous studies in Iran (8) that did verify the significance of the relationship  between Bacterial Vaginosis and preterm labor. This incongruence may be due to the different  methods of the studies or different populations which were studied. This  difference warrants more extensive studies with larger sample sizes.

This finding can also be important in deciding about the  screening of pregnant women for abnormal vaginal discharge and administration of  antibiotics in these patients. Several studies have showed that treatment of  asymptomatic bacteriuria or genital infections including Bacterial Vaginosis,  trichomoniasis, gonorrhea, and chlamydial infection can decrease the risk of preterm labor (3).  Paige 

.  (11) indicated that antibiotic therapy in this group of pregnant  women can be beneficial and prevents preterm delivery and low birth weight. The important  issue is that these women are mostly asymptomatic (11). Therefore, it is recommended  that pregnant women with abnormal vaginal discharge should be evaluated for  infection with Bacterial Vaginosis, Trichomoniasis, Gonorrhea, and Chlamydial  infection and treated accordingly (3). Some studies suggest that all pregnant women be  screened for Bacterial Vaginosis and treated accordingly in the early phases of  pregnancy (28). Some studies have assessed all pathogenic factors individually. Our study  also revealed that the only influential microorganism was E.coli which was significantly  higher (11.20% vs. 1.61%with P=0.002) in patients who experienced preterm labor.  Although previous studies have mostly shown that infection with group B streptococcus is a  risk factor of preterm labor, one single study indicated that infection with group B  streptococcus in the second trimester has a negative correlation with preterm labor (20)  which was in congruence with our results.

It has been proposed that pathogen organisms ascend via lower  genital organs to uterine and the resultant inflammation causes preterm rupture of  membranes and labor. There have been increasing studies indicating that  preterm labor and rupture of membranes are initiated by colonization of lower genital tract  with microorganisms and the inflammatory response (activation of cytokines and  proteolytic enzymes) of the host (28). The results of our study showed that the frequency of  preterm rupture of membranes was significantly higher (64.29% vs. 35.71% with  P=0.001) in patients with BacterialVaginosis. Puwar  

.  (8) achieved the same results while the results of Ziaei  


 In conclusion, we found no significant relationship between  Bacteria Vaginosis and preterm labor. However, infection with E.Coli was significantly  higher in the pre-term group. We also found that the prevalence of preterm rupture of  membranes was significantly higher in patients with Bacterial Vaginosis. We  suggest that more extensive studies with larger sample sizes and considering the confounding  factors that had not been regarded in this study can be performed.

 
 The comparison of demographic variables in cases and  controls (The values are presented as mean ± standard deviation or percent).

*: Significantly different based on Fischer’s exact test  (P<0.05)


 The  comparison of different genitourinary infections in cases and controls.


 The  comparison of different genitourinary infections in patients with ruptured and intact membranes.

*: Significantly different based on Fischer’s exact test (P<0.05)

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10. Kalinka J, Laudanski T, Hanke W, Krzeminski Z, Wasiela M. [The evaluation of prevalence and the impact of pathological microflora of the lower genital tract among women at early pregnancy on the risk of preterm delivery]. Med Dosw Mikrobiol. 2003;55(3):277-84.

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Several studies have been conducted about Bacterial Vaginosis and its relation with preterm labor that was accompanied with controversial results. The aim of this study was to compare the frequency of Bacterial Vaginosis and common genitourinary infections between term and pre-term pregnancies.

Sima Gity, MD

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