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Maternal urinary tract infection: is it independently associated with

adverse pregnancy outcome?

EFRAT MAZOR-DRAY1, AMALIA LEVY2, FRANCISC SCHLAEFFER1, & EYAL SHEINER3

1Department of Internal Medicine, Faculty of Health Sciences, Soroka University Medical Center, Beer-Sheva, Israel,

2Department of Epidemiology and Health Services Evaluation, Faculty of Health Sciences, Ben Gurion University of the

Negev, Beer-Sheva, Israel, and 3

Department of Obstetrics and Gynecology, Faculty of Health Sciences, Soroka University

Medical Center, Beer-Sheva, Israel

(Received 1 August 2008; revised 11 September 2008; accepted 15 September 2008)

Abstract

Objective. This population-based study was aimed to determine whether there is an association between urinary tractinfections (UTI) during pregnancy, among patients in whom antibiotic treatment was recommended, and maternal andperinatal outcome.

Methods. A retrospective population-based study comparing all singleton pregnancies of patients with and without UTI wasperformed. Multiple logistic regression models were performed to control for confounders.

Results. Out of 199,093 deliveries, 2.3% (n4742) had UTI during pregnancy and delivery. Patients with UTI hadsignificantly higher rates of intra-uterine growth restriction (IUGR), pre-eclampsia, caesarean deliveries (CD) and pre-termdeliveries (either before 34 weeks or 37 weeks of gestation). Although controlling for possible confounders such as maternalage and parity, using multivariable analyses, the significant association between UTI and IUGR, pre-eclampsia, CD and pre-term deliveries persisted. In contrast, no significant differences in 5-min Apgar scores less than 7 or perinatal mortality werenoted between the groups (0.6% vs. 0.6%; p 0.782, and 1.5% vs. 1.4%; p 0.704, respectively).

Conclusion. Maternal UTI is independently associated with pre-term delivery, pre-eclampsia, IUGR and CD. Nevertheless,it is not associated with increased rates of perinatal mortality compared with women without UTI.

Keywords: Urinary tract infection, pregnancy, pre-term delivery, pre-eclampsia, intra-uterine growth restriction, caesareandelivery, perinatal mortality

Introduction

Pregnancy is considered a special immunological

state characterised by activation of the innate

immunity and suppression of the acquired limb of

the immune response. These changes in the

immune system may help to promote tolerance

to the fetus as well as protect the mother

against infection [1,2]. Both pregnant animals and

women are more susceptible to infection and to the

effects of toxins of micro-organisms. For example,pregnant rats developed generalised Schwartzman

reaction after a single injection of colchicine,

whereas non-pregnant rats required a priming dose

[3,4].

Acute pyelonephritis during human pregnancy

affects 12% of women, particularly during the last

two trimesters [5] and is frequently associated with

acute respiratory distress syndrome (ARDS). In

contrast, acute pyelonephritis in non-pregnant wo-

men is rarely associated with ARDS [68]. Other

complications following acute pyelonephritis during

pregnancy include anaemia [9], transient renal

dysfunction [10], pre-term labour, intra-uterine

growth restriction (IUGR), premature rupture of

membranes (PROM) [11], pre-eclampsia [12],

sepsis and septic shock [13].

Urinary tract infections (UTI) are among the most

common bacterial infections in women, and about

10% of women are diagnosed with this disease.Importantly, UTI complicate up to 20% of pregnan-

cies and are responsible for a major part of all

antepartum admissions to the maternalfetal medi-

cine units [14]. Overall, they are one of the most

common medical complications of pregnancy [15].

Most of these infections are limited to the

lower urinary tract and are mainly manifested by

asymptomatic bacteriuria [14].

Correspondence: Eyal Sheiner, MD, PhD, Department of Obstetrics and Gynecology, Soroka University Medical Center, P.O Box 151, Beer-Sheva, Israel.

Tel: 972 8 6400774. Fax: 972 8 6275338. E-mail: sheiner@bgu.ac.il

The Journal of Maternal-Fetal and Neonatal Medicine, February 2009; 22(2): 124128

ISSN 1476-7058 print/ISSN 1476-4954 online 2009 Informa Healthcare USA, Inc.

DOI: 10.1080/14767050802488246

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In a recent study from our medical centre, we

reported that asymptomatic bacteriuria was indepen-

dently associated with pre-term delivery and accord-

ingly with low birth-weight (LBW) neonates [16].

This population-based study was aimed to deter-

mine whether there is an association between UTI

during pregnancy, among patients in whom anti-

biotic treatment was recommended, and maternaland perinatal outcome.

Materials and methods

A retrospective population-based study comparing

all singleton pregnancies of women with and without

UTI was conducted. Patients with asymptomatic

bacteriuria (n 4890) were excluded from the

analysis. Deliveries occurred during the years

19882007 at the Soroka University Medical Center.

This is the sole hospital in the Negev, the southern

part of Israel, serving the entire obstetrical popula-

tion in this region.

UTI was defined as laboratory positive urine

culture (based on the detection of more than

100,000 bacteria/ml in a single voided mid-stream

urine), in a woman with symptoms of dysuria,

urgency and frequency [15]. National health services

in Israel provide comprehensive perinatal care for all

women, and urine cultures are performed as part of

the routine prenatal care, starting during the first

appointment, usually around 1213 weeks of gesta-

tion. Women with positive urine cultures were

prescribed antibiotic treatment for 710 days accord-

ing to the type of micro-organism and antibioticbiogram.

Data were collected from the computerised

perinatal database that consists of information

recorded directly after delivery by an obstetrician.

Only four skilled medical secretaries examine the

information routinely before entering it into the

database. Coding is done after assessing the medical

prenatal care records as well as the routine hospital

documents. These procedures assure maximal com-

pleteness and accuracy of the database.

The following clinical characteristics were evalu-

ated: maternal age, fertility treatment, recurrent

abortions, gestational age at delivery and specificallypre-term delivery (defined as less than 37 weeks of

gestation). The obstetrical risk factors that were

examined were: hypertensive disorders, diabetes

mellitus, PROM, chorioamnionitis, infection of

amniotic fluid, IUGR and renal complications

(pyelonephritis, hydronephrosis, nephrolithiasis and

hydroureter). The labour characteristics and perina-

tal outcomes that were assessed included placental

abruption, labour induction, caesarean delivery

(CD) and hospitalisation days. The neonatal out-

comes that were examined included neonatal gender,

Apgar score at 1 and 5 min less than 7, birth weight

and specifically LBW (52500 g) and perinatal

mortality. The local ethics institutional review board

approved the study.

Statistical analysis was performed with the SPSS

package (SPSS 15 version, Chicago, IL). Statistical

significance was calculated using the chi-square test

for differences in qualitative variables and ANOVAfor differences in continuous variables. Stratified

analysis was performed using a multivariable logistic

regression model. Odds ratios (OR) and their 95%

confidence interval (CI) were computed. p50.05

was considered statistically significant.

Results

Out of 199,093 deliveries, 2.3% (n 4742) had UTI

during pregnancy and delivery. The clinical and

obstetrical characteristics of women with and without

UTI are displayed in Table I. Women with UTI had

a higher rate of premature delivery than those

without UTI, 15.1% vs. 7.8%, respectively

(p50.001). In addition, the group of women with

UTI delivered neonates with a significant LBW

compared with those without UTI, 13.2% vs. 8%,

respectively (p50.001). Recurrent abortions and

fertility treatment were significantly more frequent

among women with UTI. The other clinical char-

acteristics were similar between the two groups.

Maternal risk factors as well as OR and 95% CI of

pregnancy outcome of women with and without UTI

Table I. Clinical characteristics of women with and without

urinary tract infections during pregnancy and delivery.

Characteristics

Women

with UTI

(n4,742)

(%)

Women

without UTI

(n199,093)

(%) p

Maternal age (years)

518 1.0 1.3

1839 85.9 86.1

40 13.1 12.6 0.209

Fertility treatment 3.1 1.7 50.001

Recurrent abortions 6.0 5.1 0.004

Gestational age at delivery (weeks)

537 15.1 7.8

3742 81.9 87.6

42 3.0 4.6 50.001

Gender

Male 50.5 51.3

Female 49.5 48.7 0.28

Birth weight

52,500 g 13.2 8

2,5004,000 g 82.6 87.2

44,000 g 4.2 4.8 50.001

Data are expressed as means+ standard deviation or numbers and

percentages.

Maternal urinary tract infection 125

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are shown in Table II. Women with UTI had a

significantly higher rate of IUGR, labour induction,

hypertensive disorders, diabetes mellitus, PROM,

chorioamnionitis, infection of amniotic fluid, pla-

cental abruption and CD than women without UTI.

It is important to note that a variety of renal

abnormalities such as pyelonephritis, hydronephro-

sis, nephrolithiasis and hydroureter were also morecommon in patients with UTI during pregnancy than

in those without a similar complications.

We also analysed the fetal and neonatal risk factors

as well as OR and 95% CI of women with and

without UTI (Table III). Although the mean

gestational age and birth weight at delivery and

Apgar score at 1 min 57 were significantly different

between the two groups, the mean Apgar score at

5 min 57 and perinatal mortality were similar.

Although controlling for possible confounders

such as maternal age and parity, using multivariable

analyses the significant association between UTI and

IUGR, pre-eclampsia, CD and pre-term deliveries

(either before 34 weeks or 37 weeks of gestation)

persisted (Table IV). The mean (+SD) hospitalisa-

tion days was higher among patients with UTI

compared with those without UTI, 5.2+5 vs.3.4+3, respectively (p50.001).

Discussion

The most important finding of this study is that

maternal UTI during pregnancy is an independent

risk factor for pre-term delivery and IUGR. These

two important complications of pregnancy occurred

even among women who were given antibiotic

Table II. Maternal risk factors as well as odds ratios and 95% CI of pregnancy outcome of women with and without urinary tract infections.

Characteristics

Women with

UTI (n4,742)

(%)

Women

without UTI

(n199,093) (%) OR 95% CI p

Intra-uterine growth

restriction (IUGR)

3.5 2 1.8 1.52.1 50.001

Labour induction 37.7 26.4 1.7 1.61.8 50.001

Placental abruption 1.4 0.7 1.9 1.52.4 50.001

Hypertensive disorders 8 5.7 1.4 1.31.6 50.001

Mild-to-moderate

pre-eclampsia

4.3 3.3 1.3 1.11.5 50.001

Severe pre-eclampsia 1.9 1.1 1.8 1.42.2 50.001

Chronic hypertension 2.4 1.6 1.5 1.21.8 50.001

Diabetes mellitus 8.4 6.1 1.4 1.31.6 50.001Gestational diabetes 6.1 5 1.4 1.31.6 50.001

Pre-gestational diabetes 2.3 1.1 2 1.72.5 50.001

Premature rapture of

membranes (PROM)

9.7 6.6 1.5 1.41.7 50.001

Chorioamnionitis 2 0.8 2.6% 2.13.2 50.001

Infection of amniotic fluid 2 0.8 2.6 2.13.2 50.001

Renal complications

Pyelonephritis 2.4 0.0 706.9 329.41516.9 50.001

Hydronephrosis 1.4 0.1 19.9 14.926.7 50.001

Nephrolithiasis 0.8 0.1 11.4 8.116.2 50.001

Hydroureter 0.1 0.0 50.4 15.4165.3 50.001

Caesarean delivery 20.7 12.6 1.8 1.72.0 50.001

Data are presented as percentages, odds ratios (OR), 95% confidence intervals (CI) andp-values for statistical significance.

Table III. Fetal and neonatal outcome as well as odds ratios and 95% CI of women with and without urinary tract infections.

Characteristics

Women with

UTI (n4,742)

Women without

UTI (n199,093) OR 95% CI p

Gestational age (weeks) 38.6+2.7 39.2+2.2 50.001

Birth weight (g) 3,082+624 3,183+546 50.001

Apgar score 1 min 57 5.7% 4.1% 1.4 1.31.6 50.001

Apgar score 5 min 57 0.6% 0.6% 1.0 0.71.5 0.782

Perinatal mortality 1.5% 1.4% 1.0 0.81.3 0.704

Data are presented as percentages, odds ratios (OR), 95% confidence intervals (CI) andp-values for statistical significance.

126 E. Mazor-Dray et al.

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between women with and those without UTI, even

when adjusted for maternal age and parity.

The strength of this study is that this population-

based study is one of the largest studies analysing the

relationship between pregnancy outcome and UTI.

On the other hand, important information that was

missing from this study was whether the women who

were prescribed antibiotic treatment did indeed usedthe antimicrobial regimens recommended. Thus, the

compliance of patients to the antibiotic treatment in

this study is unknown. Also, we could not determine

whether the gestational age at the time of the UTI

had any clinical significance, and accordingly

whether UTI in the third trimester different than

UTI in the first trimester as far as the risk for

prematurity. Further prospective studies might an-

swer this question.

In summary, UTI during pregnancy is indepen-

dently associated with pre-term delivery, IUGR, pre-

eclampsia and CD. Further prospective studies

should investigate compliance for antimicrobial

treatment of UTI and compare the perinatal out-

come of women who where fully treated to those

partially treated. However, it should be stated that

despite the occurrence of higher rate of complica-

tions, the perinatal mortality was similar between

women with compared with those without UTI.

Declaration of interest: The authors report no

conflicts of interest. The authors alone are respon-

sible for the content and writing of the paper.

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