Urinary tract infections and kidney stones in pregnancy: Clinical sciences

During pregnancy, the urinary tract undergoes several physiologic changes that increase an individual's risk of both urinary tract infections, or UTIs, and kidney stones, or nephrolithiasis. Specifically, ureteral compression from the gravid uterus and ureteral relaxation from elevated levels of progesterone lead to urinary stasis and vesicoureteral reflux, increasing the risk of bacterial colonization and ascending infection.

Urinary tract infections in pregnancy exist on a spectrum with asymptomatic bacteriuria and acute cystitis affecting the lower urinary tract, while pyelonephritis affects the upper tract. Screening and treating the former helps prevent pyelonephritis, which is associated with maternal sepsis, disseminated intravascular coagulation, or DIC, acute respiratory distress syndrome, or ARDS, and preterm labor. Fetal complications like preterm birth and anemia may also occur.

Now, kidney stones, which refer to hard deposits often made of insoluble calcium, occur as a result of the physiologic increased urine calcium excretion and elevated urine pH. In severe cases, they may lead to ureteral obstruction, causing damage to the affected kidney or even become infected and create a renal abscess.

Your first step in evaluating a patient presenting with a chief concern suggesting a UTI or kidney stone is to perform an ABCDE assessment along with a primary obstetric survey to determine if they are stable or unstable.

If the patient is unstable, first stabilize the airway, breathing, and circulation. Obtain IV access and monitor maternal vital signs. Additionally, assess the fetal status by monitoring the fetal heart rate.

A labor evaluation may then be performed by testing for rupture of membranes and checking cervical dilation. In this situation, you should be thinking about sepsis, urosepsis, or renal abscess.

Now, when it comes to stable patients, start your assessment with a focused history and physical examination and obtain a urinalysis, or UA, and urine culture.

Now, your patient might be asymptomatic, coming in for routine prenatal care. Screening for asymptomatic bacteriuria or ASB should be performed by obtaining a routine urine culture once, preferably early in pregnancy. If a UA is performed it will be positive for leukocyte esterase and possibly nitrites. A urine culture will be positive, with a bacterial colony count of at least 100,000. In this case, diagnose asymptomatic bacteriuria.

Here’s a clinical pearl: Routine urinalysis to screen for ASB at each prenatal visit is not sufficiently sensitive for detection. One caveat is that patients with hemoglobinopathy like sickle cell trait may have higher rates of ASB and cystitis, so you might want to screen them more often.

Okay, when it comes to treatment, start with oral antibiotic therapy. First-line antibiotics include cefalexin, fosfomycin, and nitrofurantoin. Once you get sensitivity results, tailor antibiotics to them. You can consider repeating a urine culture to confirm the resolution of infection 1 to 2 weeks after antibiotic completion.

Here are some more clinical pearls! E. coli is the most commonly identified pathogen on urine culture, but it has high rates of antibiotic resistance, so avoid the use of empiric amoxicillin or ampicillin, and be sure to adjust therapy, if indicated, once urine culture sensitivity is available.

The presence of Group B streptococcus, or GBS, on urine culture at any colony count represents colonization. If the colony count is at least 100,000, treat the patient at the time of diagnosis with oral antibiotics and again during delivery with IV antibiotics as prophylaxis against early onset neonatal GBS infection. If the colony count is less than 100,000, only treat during labor with IV antibiotics.

Moving on, let’s talk about symptomatic patients. History might reveal urinary symptoms like increased frequency, urgency, dysuria, hematuria, nocturia, or suprapubic pain. UA will be positive for leukocyte esterase and possibly nitrites. Lastly, a urine culture will show a bacterial colony count of at least 100,000. At this time, you can diagnose acute cystitis.

Here’s a clinical pearl! The absence of leukocyte esterase on UA is useful in ruling out a UTI but not sufficient to make a diagnosis as contaminants from the vulva or vagina can lead to a false positive result. Nitrites, on the other hand, are the most specific finding for a UTI, but may not be present in all cases, as not all bacteria produce them.

As before, start with oral antibiotics and consider a test of cure versus simply monitoring for resolution of symptoms. If symptoms persist, repeat a urine culture.

For patients with recurrent UTIs, defined as at least two UTIs during pregnancy, you can consider antibiotic prophylaxis for the duration of the pregnancy, ideally with a lower dose once daily.