Urinary tract infection in pregnancy

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Abstract

Urinary tract infection is one of the most frequently seen ‘medical’ complications in pregnancy. The pioneering work of Edward Kass discovered that 6% of pregnant women had asymptomatic bacteriuria associated with increased prematurity and perinatal mortality compared to women with sterile urine. Screening for bacteriuria in pregnancy has become routine. The prevalence of asymptomatic bacteriuria as well as the associated complications described by Kass in 1962 are higher compared to most data collected in the 1980s and late 1990s in different populations in various parts of the world. Other factors such as vaginal colonization have been recognized as important contributors to preterm labour. The value of screening for bacteriuria has to be re-addressed considering methods, significance and costs. Treatment of urinary tract infection in pregnancy is critically reviewed.

Introduction

Urinary tract infection is one of the most frequently seen ‘medical’ complications of pregnancy. It may be symptomatic or asymptomatic. It may be present at booking or appear acutely later in pregnancy and it may be persistent or recurrent.

Section snippets

Definition

Infection of the urinary tract means organisms growing within and damaging the urinary tract. However, in clinical practice one defines this entity in relation to the number of bacteria in a voided urine sample. Significant bacteriuria is equal to or greater than 105 of the same organism per ml of urine. Symptomatic bacteriuria is defined as equal to or greater than 102 coliform organisms per ml of urine plus pyuria, greater than or equal to 105 of other pathogens per ml, or any growth of

Asymptomatic bacteriuria

The report of Kass in 1962 described that 6% of pregnant women had asymptomatic bacteriuria [1], [2]. Half these patients were treated with a long acting sulphonamide or nitrofurantoin and the other half were given placebo. Their pregnancy outcome was compared with a control group of 1000 women with sterile urine. This control group had a prematurity rate of 9% and perinatal mortality of 20 per 1000, which are both high by present day standards. The treated asymptomatic bacteriurics had a

Symptomatic bacteriuria

The use of the term asymptomatic bacteriuria in pregnancy is rather paradoxical because most pregnant women will experience bladder pain, urinary frequency and urgency. However, the term symptomatic bacteriuria is used where there is evidence of upper urinary tract infection. This is usually associated with pyrexia, abdominal and loin pain or tenderness as well as the demonstration of bacteriuria. The risk of acute pyelonephritis developing in a patient with asymptomatic bacteriuria is

The impact of bacteriuria

In the past, it has been claimed that bacteriuria increased the risk of anaemia and hypertension found during pregnancy. It is unlikely that this is a real association although there may be a link between bacteriuria and both intrauterine growth restriction and preterm labour. One of the problems in interpreting earlier studies is that prematurity was defined as delivery with a birth weight of less than 2.5 kg rather than the definition of delivery of less than 37 weeks gestation. Therefore,

Treatment of bacteriuria

If patients are seen with acute pyelonephritis they can be effectively treated with systemic gentamicin or cephalosporins. If they have asymptomatic bacteriuria then a single dose of cephalexin, co-trimoxazole, or amoxycillin appears effective. Those patients who get recurrent infection should be given 50 mg nitrofurantoin at night for prophylaxis. It is probably better to avoid trimethoprim in the first half of pregnancy and sulphonamides in the last month before delivery. Tetracylines should

How to screen

The diagnosis of asymptomatic bacteriuria is made on a urine specimen with appropriate microscopic examination followed by culture. The cost of this is currently approximately £4. An alternative approach would be to use a Multistix which will detect blood, protein, nitrites and leukocyte esterase at an approximate cost of 15p, but the sensitivity of such testing is reduced and positive results will only be obtained with Gram-negative organisms or in the presence of pyuria. Rouse et al. [11]

The current status

One must address how far we have progressed since the pioneering work of Kass in understanding the significance of asymptomatic bacteriuria. The link between infection and preterm labour is more understood now and it is more likely that the presence of a combination of organisms within the vagina contribute to this problem rather than the presence of a pure organism identified within the urine. Secondly, there has been a great improvement in perinatal care especially the management of

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