Urinary tract infections in pregnancy: types, symptoms, diagnosis and treatment

Urinary tract infections are the most common bacterial infections encountered during pregnancy.

Urinary tract infections in pregnancy can be classified into 4 categories,

1.      Asymptomatic bacteriuria

2.      Cystitis and urethritis

3.      Acute pyelonephritis

4.      Reflux nephropathy

In these asymptomatic bacteriuria is the most common one. 
Symptomatic infection may involve lower urinary tract causing cystitis or it may involve renal calyces, pelvis and parenchyma causing pyelonephritis.

Pregnant women are more prone to urinary tract infections because, progesterone, the hormone of pregnancy reduces the ureteral tone and peristalsis, and relaxes the bladder wall allowing reflux through the incompetent vesico-ureteral valves. 
This results in stasis of urine and bacterial proliferation leading to cystitis in the lower urinary tract  and dilated ureters, increased pressure in the renal pelvis in the upper urinary tract with bacterial proliferation leading to pyelonephritis.

The organisms which cause urinary tract infection are commonly those in the normal pelvic flora like Escherichia coli, Klebsiella, Proteus, Group B streptococcus (GBS), Enterococci and Staphylococci in order of frequency.

The E coli is the most common organism causing urinary tract infection in pregnancy, in these the strain  causing nonobstructive pyelonephritis will have adhesions or P-fimbriae to enhance their virulence.

In puerperium also urinary tract infections are common because of  bladder stasis, diminished bladder sensation because of trauma of labour or due to epidural or spinal anesthesia. 
The discomfort caused by episiotomy, periurethral lacerations or vaginal wall hematomas may lead to decreased sensation of bladder distension. 
Postpartum diuresis will worsen the over distension of bladder. Catheterization of bladder in labour can also lead to urinary tract infection.

1. Asymptomatic bacteriuria:

Asymptomatic bacteriuria is defined as persistent actively multiplying bacteria within the urinary tract in a woman with no symptoms. 
A mid stream clean-voided sample containing more than 100,000 organisms of same species per ml is diagnostic of asymptomatic bacteriuria. 
But patients even with low bacterial counts also better to be treated as pylonephritis can develop in some women with counts between 20,000 to 50,000 organisms/ml.

The prevalence in non-pregnant women is 5 to 6%. 
Incidence during pregnancy is 2 to 7% and it depends on parity, race and socioeconomic status. 
 Highest  incidence is seen in African – American multiparas with sickle cell trait and lowest incidence is in affluent white women with low parity.

Routine screening for bacteriuria at first prenatal visit is advised. 
Bacteriuria if noticed in the first visit itself with  culture is negative the chances of developing urinary infection is less. 
But if not treated about 25% of patients are having chance to develop acute symptomatic infection. 
Doing culture is cost effective only in high prevalence areas. 
In case of low prevalence less expensive methods like leukocyte esterase-nitrate dipstick test can be used.

Some studies showed a association between asymptomatic bacteriuria and increased incidence of low-birth weight infants, preterm delivery, hypertension, preeclampsia, maternal anemia. 
But these are more associated with serious urinary tract infections.

In some women bacteriuria may persist or recurs or may turn into symptomatic infection after delivery. 
In some women congenital abnormalities in the urinary tract noticed making them susceptible to infections.

Treatment: 
for the treatment of bacteriuria  many antimicrobial regimens are available.

Recommended single dose treatment regimens:

 Amoxicillin, 3 g

Ampicillin, 2 g

Cephalosporin, 2 g

Nitrofurantoin, 200 mg

Trimethoprim-sulfamethoxazole, 320/1600 mg

Three days course regimens:

 Amoxicillin, 500 mg tid (three times a day)

 Ampicillin, 250 mg qid (four times a day)

Cephalosporin, 250 mg qid

Ciprofloxacin, 250 mg bid(two times a day)

Levofloxacin, 250 mg daily

Nitrofurantoin, 100 mg bid

Trimethoprim-sulfamethoxazole, 160/800 mg bid.

Other regimens:

Nitrofurantoin, 100 mg qid for 10 days.

Nitrofurantoin, 100 mg at bed time for 10 days.

In case of treatment failure with above regimens:

Nitrofurantoin, 100 mg qid for 21 days.

In case of bacterial persistence or recurrence:

Nitrofurantoin, 100 mg at bed time  for remainder of pregnancy.

2. Cystitis and urethritis:

Cystitis is the bladder infection which may develop during pregnancy without antecedent covert bacteriuria.

The clinical features will be dysuria, urgency and frequency, some systemic findings like fever malaise may also present in some cases. 
Pyuria or bacteriuria may be present. 
Microscopic hematuria may be there sometimes gross hematuria can be seen. 
Sometimes cystitis can turn into upper urinary tract infection. 
Around 40% pregnant women with acute pyelonephritis will have previous lower urinary tract infection.

Treatment:

Three days course therapy:

Amoxicillin, 500 mg tid (three times a day)

 Ampicillin, 250 mg qid (four times a day)

Cephalosporin, 250 mg qid

Ciprofloxacin, 250 mg bid(two times a day)

Levofloxacin, 250 mg daily

Nitrofurantoin, 100 mg bid

Trimethoprim-sulfamethoxazole, 160/800 mg bid.

Single dose therapy may not be effective.

Urethritis :
If patient presents with frequency, urgency, dysuria and pyuria with negative culture for bacterial growth it may be due to urethritis caused by Chlamydia trachomatis, which will be present in genitor urinary tract commonly presenting with mucopurulent cervicitis. 
It can be treated with erythromycin.

3. Acute pyelonephritis:

Acute pyelonephritis is the renal infection which is the most common serious medical complication of pregnancy. 
Genitourinary infection is the second most common reason for a nondelivery admissions.

Urosepsis is the leading cause of sepsis shock during pregnancy. 
It may lead to increased incidence of preterm babies with cerebral palsy. But long term sequelae to mother are less.

Clinical features:

It  is more common in second trimester  the associated risk factors are young age and nulliparity. 
Normally it will present unilaterally and more than 50% on right side because of uterine dextrorotation leading to right ureter compression.
 In 25% of cases it is bilateral.

Symptoms: 
 The onset of acute pyelonephritis is usually abrupt with clinical features of fever of variable degrees with chills, aching pain at the lumbar region either unilateral or bilateral depending on the involvement. 
Associated anorexia, nausea or vomiting may be seen.

Sepsis syndrome may present in some cases with thermoregulatory instability with high spiking fever up to 42⁰C with hypothermia in between with temp up to 34⁰C.  
Fetal bradycardia may be seen during these fluctuations of temperature, which will recover with treatment.

Markedly increased cardiac output is seen because of lowered systemic vascular resistance.

Renal dysfunction can be seen in 20% of patients.

Endotoxin induced alveolar injury and pulmonary edema leading to respiratory insufficiency may occur it may turn into respiratory distress syndrome.

Endotoxin activity may lead to uterine activity but usage of beta agonists for tocolysis may worsen he respiratory insufficiency by sodium and fluid retention leading to alveolar flooding.

Endotoxin may also lead to acute anemia by causing hemolysis but haemoglobin regeneration is not affected as erythropoietin production remains unaltered.

Signs: 
Tenderness can be elicited on percussion in one or both costovertebral angles.

Diagnosis:

Urine microscopy examination:  shows many leukocytes sometimes in the form of clumps and numerous bacteria.

Urine and blood cultures:  
E coli is isolated in urine or blood in 75 to 80% of cases. Klebsiella is seen in 10% of cases, Proteus or  Enterobacter in 10% of cases. 
In 15 to 20% of cases bacteremia is seen.

As chances of developing renal dysfunction are there serum creatinine, electrolytes and hemogram investigations are to be done.

Differential diagnosis:

Labor,  chorioamnionitis, appendicitis, placental abruption or infracted myoma etc.

Management:

Patient to be hospitalised. Investigations as above said to be sent.

Vital signs like pulse rate, blood pressure, temperature and urine output to be monitered. 
If needed foley’s catheterisation can be done.

Intravenous hydration with crystalloids to be given to maintain the urinary output of up to or above 30 ml/hr.

Antibiotics to be given intravenously. 
Many patients will respond within 48 hrs.

If patient is suffering from respiratory distress chest radiograph can be taken to rule out alveolar damage or pulmonary edema.

Hematological and urinary investigations to be repeated in 48 hrs.

Patient can be shifted to oral antibiotics when she is afebrile. 
And can be discharged when afebrile upto 24 hrs. 
But the drugs to be continued for 7 to 10 days.

Urine culture to be repeated after 1 to 2 weeks of  antimicrobial therapy.

Very few number of patients are fit to be treated as outpatients from the beginning.

In case of non responders ultrasonography can be done to look for the presence of urinary tract obstruction, abnormal dilatation of ureter or pyelocaliceal junction, presence of stones, intra renal or perinephric abscess, phlegman etc.

Plain abdominal radiograph, intravenous pyeloghraphy, or magnetic resonance urography are also useful in diagnosing the stones or to visualise the collecting system.

In case of obstruction it can be relieved by cystoscopic placement of double-J ureteral stent or by percutaneous nephrostomy. 
In some women surgical treatment may be required.

Recurrence of infection may occur in 30 to 40% of cases. 
In these cases Nitrofurantoin 100 mg at bed time to be used for the remainder of pregnancy.

4.Reflux nephropathy:

Infection leading to chronic interstitial nephritis that is called as chronic pyelonephritis  will be frequently associated with radiological scarring due to ureteral reflex with voiding, so it is called as reflux nephropathy.

If significant renal damage occurs it will lead to hypertension. 
Childhood infections can lead to renal lesions after surgical correction also they are prone to infection during pregnancy.

Less than half of the women with reflux nephropathy will have preceding cystitis, acute pyelonephritis or obstructive nephropathy. 
Even with recurrent urinary infections only few will progress to renal damage.

Maternal and fetal prognosis depends on the extent of renal damage. 
Maternal complications will be increased in case of impaired renal function and bilateral renal scarring.