Dipa S Pitre

Purvi K Patel

Suman P Bhooker

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National Journal of Community Medicine│Volume 6│Issue 1│Jan – Mar 2015 Page 121 
 
 
 
ORIGINAL ARTICLE 
pISSN 0976 3325│eISSN 2229 6816 
Open Access Article  
www.njcmindia.org 
 
PREDICTIVE VALUE OF VARIOUS RISK FACTORS FOR 
PRETERM LABOR 
Purvi K Patel1, Dipa S Pitre2, Suman P Bhooker3 
 
 
Financial Support: None declared 
 
Conflict of interest: None declared 
 
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copyrights of this article. However, 
reproduction of this article in the 
part or total in any form is permis-
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the source. 
 
How to cite this article: 
Patel PK, Pitre DS, Bhooker SP. 
Predictive Value of Various Risk 
Factors for Preterm Labor. Natl J 
Community Med. 2015; 6(1):121-5. 
 
Author’s Affiliation: 
1Associate Professor; 2Assistant 
Professor; 3Senior resident, Dept. of 
Obstetrics & Gynecology, Medical 
College, Baroda 
 
Correspondence: 
Dr. Purvi K Patel 
E-mail: drpurvipatel@gmail.com 
 
Date of Submission: 27-11-14 
Date of Acceptance: 15-02-15 
Date of Publication: 31-03-15 
 
ABSTRACT 
 
Objective: The objectives of this study were to study the various 
etiological factors responsible for onset of preterm labor and to 
evaluate the predictive value of these risk factors for spontaneous 
preterm labor. 
Methods: This prospective comparative study was conducted 
over a period of 1 year and included 240 women; of which 120 in 
preterm labor were enrolled in the study group and 120 with term 
pregnancy in labor were enrolled in the control group. History, 
clinical examination and investigations were carried out and risk 
factors for preterm labor were noted and analyzed to find out the 
predictive value of the risk factors for preterm labor. 
Results: Maximum numbers of patients (31.6%) were in the 35-36 
weeks gestational age group. When both the groups were com-
pared as regards risk factors, the cases showed a high incidence of 
infections; 21.7% incidence of chorioamnionitis, 32.5% incidence 
of bacterial vaginosis and a 12.5% incidence of urinary tract infec-
tions. Prior second trimester abortion was found in 13.3% cases 
and a history of prior preterm birth was found in 15% cases. Uter-
ine over distension was observed in 20.83% cases. Maternal medi-
cal disorders were present in 60% cases. 
Conclusions: Multiple pregnancy, Prior preterm birth, Infections, 
Prior second trimester abortions and medical disorders in mother 
are strongly associated with an increased risk of preterm labor. 
 
Key words: Preterm, labor, predictive value, pregnancy 
 
INTRODUCTION 
Preterm labor is defined as the onset of labor in 
women before 37 completed weeks of gestation. 
The incidence of preterm labor varies from 10-
15% of all pregnancies.1 Currently, preterm labor 
is one of the most challenging problems con-
fronting the obstetricians and the perinatologists, 
as prematurity accounts for 50-75% of the perina-
tal mortality.2 
There are various causes of preterm labor, 
though in a majority of cases, the cause is un-
known. Infections, maternal medical and surgi-
cal disorders, uterine over-distension, uterine 
anomalies, placental anomalies and fetal pathol-
ogies are amongst the causes for preterm labor. 
There are some factors associated with preterm 
labor like socio-economic, genetic, constitutional 
and obstetric. 
During the past two decades, we have come 
closer to understanding the etiology of sponta-
 
 
       Open Access Journal │www.njcmindia.org  pISSN 0976 3325│eISSN 2229 6816 
National Journal of Community Medicine│Volume 6│Issue 1│Jan – Mar 2015 Page 122 
 
 
neous preterm birth, but we still need better 
markers to identify women at risk for preterm 
delivery. The present study was undertaken to 
identify the various factors responsible for pre-
term labor. With this background, the objectives 
of this study were to study the various etiologi-
cal factors responsible for onset of preterm labor 
and to evaluate the predictive value of these risk 
factors for spontaneous preterm labor. 
 
METHODS 
The study group consisted of women admitted 
with the diagnosis of preterm labor and the con-
trol group consisted of pregnant women admit-
ted with labor pains at term in the department of 
Obstetrics and Gynecology, SSG Hospital, Baro-
da. This prospective comparative study was 
conducted on 240 women; of which 120 in pre-
term labor were enrolled in the study group and 
120 with term pregnancy in labor were enrolled 
in the control group. The study duration was 1 
year (from 1 August 2011 to 31 July 2012) 
Inclusion criteria for the study group: 
1. Gestational age between 28 to 37 weeks 
2. Regular uterine contractions occurring at a 
frequency of at least 4 in 20 minutes or 8 in 
60 minutes synchronizing with pain 
3. Cervical dilatation greater than 1cm with 
effacement of cervix 
4. Intact membranes 
 
Exclusion criteria in the study group:  
1. Patients of preterm labor with ruptured 
membranes 
2. Patients not willing to give consent for the 
study 
3. Intra-uterine fetal death 
4. Eclampsia 
5. Severe obstetric bleeding; either abruptio 
placenta or placenta previa 
 
Patient information sheet was given to all wom-
en enrolled in the study and an informed written 
consent for participation in the study was taken. 
Detailed history of the patients was taken. The 
data were collected as regards the age, parity, 
educational status, social and environmental his-
tory, obstetric history maternal medical condi-
tions and any treatment. General, systemic, ab-
dominal, speculum and vaginal examinations, 
routine investigations, CRP, urine culture and 
sensitivity, high vaginal swab culture and sensi-
tivity, and ultrasonography were carried out. 
Details of neonate at birth were recorded. Mater-
nal and neonatal follow-up was done up to dis-
charge from the birth. 
Prevalence rate of different risk factors were cal-
culated and compared. The data was analyzed 
calculating odd’s ratio and P value with help of 
medcalc statistical software for windows. P value 
of <0.05 was considered statistically significant. 
Statistical tools like sensitivity, specificity, posi-
tive predictive value, and negative predictive 
value were used to evaluate and identify various 
risk factors. 
 
RESULTS 
The study included 120 cases and 120 controls 
that were enrolled during the study period of 1 
year. Both the groups were comparable with re-
gards to age, parity and residential status. As 
seen in the table 1, maximum numbers of pa-
tients (38 i.e.31.6%) were in the 35-36 gestational 
age group. 
Many patients had more than one predisposing 
factor so the sum doesn’t come up to 100%. As 
seen from the above table, heavy work, smoking, 
tobacco chewing, pre-pregnancy height and 
weight were not found have a statistically signif-
icant association with occurrence of spontaneous 
preterm labor. Low socio-economic status, prior 
second trimester abortion and inadequate ante-
natal care had a significant association with pre-
term births. Prior preterm deliveries, uterine 
over-distension and maternal medical disorders 
were found to have a highly significant associa-
tion with preterm labor. 
Bacterial vaginosis accounted for 32.5% and uri-
nary tract infections for 12.5% of cases. 21.7% 
cases were CRP positive as compared to only 
4.2% controls suggesting a role of infection and 
inflammation in preterm labor. Other infections 
associated with systemic manifestations in form 
of fever were seen in 6.7% cases as compared to 
0.8% controls.  
 
Table 1: Gestational age wise distribution of 
cases 
Gestational age in weeks Number of cases (%) 
28-30 19 (15.8) 
31-32 27 (22.6) 
33-34 36 (30) 
35-36 38 (31.6) 
Total 120 (100) 
 
 
 
       Open Access Journal │www.njcmindia.org  pISSN 0976 3325│eISSN 2229 6816 
National Journal of Community Medicine│Volume 6│Issue 1│Jan – Mar 2015 Page 123 
 
 
 
Table 2: Various predisposing factors under study and their significance 
Predisposing factors Cases 
n=120 (%) 
Controls 
n=120 (%) 
OR with 95% CI P value 
Low socio-economic status 54 (45) 34 (28.3) 2.02 (1.18-3.45) 0.01* 
Heavy work 24 (20) 15 (12.5) 1.75 (0.86-3.53) 0.11 
Pre-pregnancy weight < 45 kg 28 (23.3) 25 (20.8) 1.15 (0.62-2.13) 0.64 
Height < 145 cm 22 (18.3) 16 (13.3) 1.45 (0.72-2.94) 0.29 
Smoking 6 (5) 2 (1.7) 3.10 (0.61-15.70) 0.17 
Tobacco chewing 12 (10) 6 (5) 2.11 (0.76-5.82) 0.14 
Prior second trimester abortion 16 (13.3) 5 (4.2) 3.53 (1.25-9.99) 0.01* 
Prior preterm births 18 (15) 4 (3.3) 5.11 (1.67-15.61) 0.004* 
Inadequate antenatal care 64 (53.3) 45 (37.5) 1.90 (1.13-3.18) 0.014* 
Maternal medical disorders (anemia, 
Pregnancy induced hypertension, 
jaundice, cardiac disease, epilepsy, 
diabetes mellitus, tuberculosis etc) 
72 (60) 19 (15.8) 7.97 (4.32-14.69) <0.0001* 
Uterine over distension 
(polyhydramnios, multiple pregnancy) 
25 (20.83) 1 (0.8) 31.31 (4.16-235.34) 0.0008* 
*significant (p < 0.05) 
Odd’s ratio and P value calculated by Medcalc software 
 
Table 3: Infections as a cause of preterm labor 
Infections Cases 
n=120 (%) 
Controls 
n=120 (%) 
OR with 95% CI P value 
CRP reactive (chorioamnionitis) 26 (21.7) 5 (4.2) 6.36 (2.35-17.20) 0.0003* 
Bacterial vaginosis 39 (32.5) 10 (8.3) 5.29 (2.49-11.23) <0.0001* 
Urinary tract infection 15 (12.5) 5 (4.2) 3.28 (1.15-9.35) 0.025* 
Other infections (associated with fever) 8 (6.7) 1 (0.8) 8.5 (1.04-69.05) 0.04* 
*significant (p < 0.05) 
Odd’s ratio and P value calculated by Medcalc software 
 
Table 4: Predictive value of significant risk factors 
Risk factor Sensitivity (%) Specificity (%) PPV (%) NPV (%) 
Chorioamnionitis 21.7 95.8 83.9 55.0 
Bacterial vaginosis 32.5 91.7 79.6 57.6 
Urinary tract infection 12.5 95.8 75.0 52.3 
Prior 2nd trimester abortion 13.3 95.8 76.2 52.5 
Prior preterm birth 15.0 96.7 81.8 53.2 
Maternal medical disorders 60.0 84.2 79.1 67.8 
Multiple pregnancy 17.5 99.2 95.5 54.6 
PPV=Positive predictive value & NPV=Negative predictive value 
 
Chorio-amnionitis and bacterial vaginosis were 
found to be highly significant statistically as 
causes of preterm delivery. Urinary tract infec-
tions and other systemic infections were also 
found to have significant association with occur-
rence of preterm births.  
The above table shows the predictive value of 
various risk factors. Chorioamnionitis, bacterial 
vaginosis, urinary tract infection, prior second 
trimester abortions, prior preterm birth and mul-
tiple pregnancy are the strongest predictors of 
preterm births. 
DISCUSSION 
When the spontaneous preterm births were sub-
classified based on gestational age, this study 
observed that severe prematurity (28-30 weeks) 
was noted in 15.8% cases. 31-34 weeks gestation-
al age was noted in 52.6% cases and 35-36 weeks 
gestational age (late preterm or near term) was 
observed in 31.6% cases. This distribution is 
found worldwide and the late preterm neonates 
are also associated with significant morbidities in 
the neonatal period. In this study, however, we 
did not include extreme prematurity. 
 
 
       Open Access Journal │www.njcmindia.org  pISSN 0976 3325│eISSN 2229 6816 
National Journal of Community Medicine│Volume 6│Issue 1│Jan – Mar 2015 Page 124 
 
 
The hospital where this study was conducted 
largely caters to the low socio-economic group of 
women. In this study, low socio-economic status 
was found to be a significant risk factor in pre-
term births. Studies evaluating the role of socio-
economic status in preterm deliveries have 
found similar association.3,4 In this study, heavy 
work was not found to have a statistically signif-
icant association with preterm births. The data 
on effect of work on causation of preterm births 
is contradictory. A recent study found that night 
work may be related to early but not late preterm 
birth, whereas physically demanding work did 
not strongly predict risk.5 
Maternal anthropometric parameters had no sig-
nificance on preterm deliveries in this study. 
Similar findings were observed by Honest et al.6 
In this study, we did not find an association of 
preterm births with smoking and tobacco chew-
ing. However, studies do find that smoking is 
moderately associated with preterm birth. The 
more the mother smokes, the greater the risk.4 
One of the strongest clinical risk factors for pre-
term birth is a prior preterm birth.7,8 Same was 
found in this study. Inadequate antenatal care 
was found to be a significant risk factor for pre-
term birth. Blondel et al9 has found similar re-
sults. Maternal medical disorders were a strong 
predictor of preterm birth in this study. Similar 
results have been noted in a study.10 Multiple 
gestations have an increased risk for preterm 
births, and result in 12-27% of all preterm deliv-
eries.11 In this study too we noted a highly signif-
icant association of multiple pregnancies and 
preterm deliveries. 
Infections are often the most common risk factors 
of preterm births. Genital tract infections account 
for about 25-40% of preterm deliveries. Women 
with Chlamydia trachomatis, Gardnerella 
vaginalis, Trichomonas vaginalis, Neisseria gon-
orrhoeae, Treponema pallidum, have a higher 
rate of preterm births. Still, infection is difficult 
to detect due to the limitations of conventional 
microbial techniques and the difficulties in ob-
taining appropriate diagnostic samples during 
pregnancy.12 Spontaneous preterm deliveries 
that occur before the 34th week of gestation, 
have been strongly associated to intrauterine 
infection. Intrauterine inflammation most com-
monly presents as chorioamnionitis, which is 
defined as inflammation (caused usually by bac-
terial infection) of the chorion, amnion, and pla-
centa. Intrauterine inflammation is one of the 
most common antecedents of premature birth.11 
Chorioamnionitis causes an inflammatory cas-
cade that results in preterm labor. Chorioamni-
onitis (clinical and histologic combined), compli-
cates as many as 40–70% of preterm births with 
premature membrane rupture or spontaneous 
labor.13 In this study too, 21.7% cases were CRP 
positive as compared to only 4.2% controls sug-
gesting a role of infection and inflammation in 
preterm labor. Lamont concluded that infection 
is responsible in 40% cases for preterm labor and 
suggested that the earlier the abnormal genital 
tract colonization occurs, the greater is the risk of 
adverse outcome.14 
Bacterial vaginosis accounted for 32.5% and uri-
nary tract infections for 12.5% of cases in this 
study. The results are comparable to studies by 
Glantz et al15, Hiller et al16 and Meis et al.17 In a 
large recent meta-analysis of more than 20,000 
women, Leitich et al18 reported that bacterial 
vaginosis more than doubled the risk of preterm 
birth. 
Table 4 shows the predictive value of various 
risk factors. Beverly19 observed similar results in 
his study. Accurate prediction of preterm births 
among asymptomatic pregnant women and 
those with threatened preterm labor might offer 
an opportunity to target more intensive antenatal 
surveillance and prophylactic measures to those 
most likely to benefit from preventive modali-
ties.20 
 
CONCLUSIONS 
Multiple pregnancy, prior preterm birth, Infec-
tions, prior second trimester abortions and medi-
cal disorders in mother are strongly associated 
with an increased risk of preterm labor. Modifia-
ble risk factors can be identified and modified as 
primary prevention strategies. Risk factors like 
previous preterm birth, multiple pregnancies 
and placental abnormalities cannot be modified 
hence preventive efforts should be directed to-
wards modifying working conditions during 
current pregnancy, good antenatal care, and ap-
propriate management of infections and medical 
disorders. 
 
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       Open Access Journal │www.njcmindia.org  pISSN 0976 3325│eISSN 2229 6816 
National Journal of Community Medicine│Volume 6│Issue 1│Jan – Mar 2015 Page 125 
 
 
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PREDICTIVE VALUE OF VARIOUS RISK FACTORS FOR PRETERM LABOR

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PREDICTIVE VALUE OF VARIOUS RISK FACTORS FOR PRETERM LABOR

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