KEY POINTS
• Understand the basic physiologic changes accompanying pregnancy in the genitourinary system.
• Recognize and manage basic genitourinary diseases in the pregnant patient.
• Understand the complex and multidisciplinary approach needed to manage chronic renal disease in pregnancy.
ALTERATIONS OF NORMAL RENAL FUNCTION
Background
• Pregnancy induces anatomic and physiologic changes in the genitourinary system. The alterations affect function, thus changing baseline and normative values in pregnancy as compared to the nonpregnant state.
• Changes begin in the first 5 to 7 weeks’ gestation and resolve between 6 and 12 weeks postpartum (1).
Pathophysiology
Anatomic Alterations
• Renal size increases approximately 1 to 1.5 cm. These changes are secondary to
• Increase in renal vascular volume
• Increase in capacity of the collecting system
• Glomerular hypertrophy
• Renal volume increases 30% (1).
• Ureteral dilation:
• Changes begin in the first trimester.
• Normal pregnancy measurement:
Up to 2 cm
Right side affected to a greater extent than the left
• Dilation may be due to
Smooth muscle relaxation due to progesterone effects that is supported by:
– Maternal ureteral dilation prior to 14 weeks’ gestation
– Dilation of the fetal ureter as seen on sonogram
Inhibition of ureteral peristalsis due to prostaglandin E2
Mechanical obstruction:
– Due to enlarging uterus
– Right ureteral dilation greater than left ureteral dilation may be due to
∗ Dextrorotation of the uterus
∗ Compression of the right ovarian vein complex as it crosses over the right ureter
∗ Cushioning of the left ureter by the sigmoid colon
• Physiologic dilation does not extend below the pelvic brim.
Dilation below the pelvic brim is pathologic.
• Resolves by 3 to 4 months postpartum.
• Renal pelvicalyceal dilation:
• Changes begin in the first trimester
• Dilation may be due to
Decreased ureteral peristalsis
Hormonal influences of estrogen and progesterone
Mechanical obstruction due to enlarging uterus
• Resolves by 3 to 4 months postpartum.
Physiologic Changes
• Renal blood flow (RBF) may increase up to 75% due to (2, 3)
• Increase in cardiac output (CO) of 30% to 40%
• Decrease in peripheral vascular resistance (PVR)
Normal blood pressures decreases 10 mm Hg.
• Increase in blood volume of 50% (1, 3, 4)
Plasma and red cell volume begin to increase in the first trimester.
Plasma volume is increased due to decreased PVR and stimulation of sodium retention that leads to an increase of total body water.
• RBF begins to decrease at 34 weeks and may drop by 25%.
• Glomerular filtration rate (GFR) is increased by approximately 50% due to the increased RBF, which is seen by 16 weeks’ gestation.
• GFR remains elevated until 36 weeks, and then declines to prepregnancy values several weeks postpartum (1).
• Increased GFR and renal tubular adaptation leads to (4)
Serum creatinine decreasing from an average of 0.8 mg/dL to 0.5 mg/dL.
– If persistently greater than 0.9 mg/dL, then underlying renal disease must be suspected
Blood urea nitrogen decreasing from 13 mg/dL to 9 mg/dL.
Creatinine clearance increases from 120 mL/min in nonpregnant states to 150 to 200 mL/min in pregnancy.
Uric acid levels decrease from 5 mg/dL to 2.4 mg/dL but will increase in late pregnancy due to decreases in RBF.
Glucosuria can be a normal finding.
– Ninety percent of women with normal blood glucose levels spill 1 to 10 g of glucose per day.
Proteinuria and aminoaciduria are increased, but proteinuria should not exceed 300 mg/24 hours in the normal pregnant patient.
• GFR remains stable while RBF decreases (1, 2).
• Resetting of vasopressin osmoreceptor with lowered thirst threshold combined with unimpaired water clearance leads to (5)
• Decrease in plasma osmolality of approximately 10 mOsm per kg H2 O
• Decrease in serum sodium to 135 mEq/L
Sodium of 140 mEq/L or greater is indicative of hemoconcentration.
• Potassium is retained to support fetal–placental development.
• May unmask potassium excretion defects associated with
Sickle cell disease
Diabetes mellitus
Renal insufficiency
• May lead to hyperkalemia, arrhythmia, and death.
• Renal compensation for progesterone stimulation of the respiratory center and subsequent respiratory alkalosis occurs by (1)
• Decrease in PCO2 by 10 mm Hg.
• Increase in pH to an average of 7.44.
• Increased excretion of serum bicarb to 18 to 20 mEq/L to compensate for alkalosis.
• Note that these changes place the mother and fetus at increased risk of exposure to acidemia in times of infection or stress.
Evaluation
Initial Laboratory Evaluation
• Urinalysis, urine culture, and blood pressure are an initial screen for underlying renal disease.
• Abnormalities will prompt further evaluation with a basic metabolic panel and a 24-hour urine collection for protein and creatinine.
• Creatinine excretion is approximately 15 to 20 mg/24 h/kg and will yield information regarding the compliance with collection of the 24-hour urine sample.
• Hematuria or proteinuria should trigger further workup for renal disease.
• Hypertension prior to 20 weeks’ gestation should also raise suspicion of underlying renal disease.
URINARY TRACT INFECTIONS
Background
Definition
• Asymptomatic bacteriuria (ASB): Minimum of 105 per mL of a single organism on two consecutive, clean-catch urine specimens or ≥ 102 per mL of a single organism in a single catheterized specimen (6).
• Urinary tract infection (UTI): Minimum of 103 per mL of a single organism in the presence of symptoms (2).
• Uncomplicated UTI: Infection of the lower tract in women who do not have structural or functional lesions in the genitourinary system.
• Complicated UTI: UTI with pyelonephritis or where the patient is predisposed to reduced efficacy of treatment due to functional or structural abnormalities. By definition, all UTIs in pregnancy fall into this category (7).
• Pyelonephritis: Characterized by fever of greater than 38°C, chills, flank pain, costovertebral angle tenderness, nausea, emesis, anorexia, and either 20 bacteria per high-power field or pyuria (8).
Pathophysiology
• Untreated ASB progresses to a symptomatic UTI in 30% to 40% of patients.
• Vesicoureteral reflux, slowed emptying, and dilated renal collecting system due to hormonal factors and pressure from the gravid uterus predispose patients to upper and lower UTIs.
• Aminoaciduria and glucosuria may promote bacterial growth.
• Increased incidence in women who are older, higher parity, of lower socioeconomic status, history of UTI, anatomic or functional abnormality, and affected by diabetes mellitus or sickle cell trait or disease (9).
Etiology
• Normal vaginal flora
• Most common organisms
• Escherichia coli is isolated in 70% of cases.
• Klebsiella is isolated in 3% of cases.
• Proteus is isolated in 2% of cases.
• Gram-positive cocci such as group B streptococcus are implicated in 10% of cases.
Epidemiology
• ASB occurs in 2% to 13% of pregnancies (9).
• Symptomatic UTIs complicate 1% to 2% of pregnancies.
• Incidence of UTI is unchanged if prior ASB is recognized and treated.
• Recurrent UTIs: Two or more bladder infections in 1 year (9).
• Consider evaluation for underlying renal anomaly.
• Pyelonephritis complicates an additional 1% to 2% of pregnancies (6).
• Most common nonobstetric etiology for hospitalization.
• Ninety percent of cases may be avoided by treatment of ASB.
• May be associated with a reversible decrease in GFR.
• Ninety percent of cases occur in the second and third trimesters.
Evaluation
Laboratory Tests
• ASB or UTI
• Urinalysis and urine culture.
• Follow up culture 2 weeks after treatment to assess for eradication.
• Pyelonephritis
• Urinalysis, urine culture, blood cultures, basic metabolic panel to assess creatinine, and electrolytes
Treatment
Procedures
• ASB or UTI
• Treat with oral antibiotics for 3 to 7 days.
• Thirty percent recurrent infection rate regardless of treatment regimen.
• Recurrent infections require 10 days of oral antibiotic therapy.
• Complicated UTI or recurrent UTIs
• Treat with oral antibiotics for 10 days.
• Daily suppressive therapy for the remainder of pregnancy for history of recurrent UTIs or recurrent infections complicating the antenatal course.
• Pyelonephritis
• Admission for inpatient treatment
• Antibiotics for 24 hours after resolution of flank pain and fever
• Combined IV and oral course for 10 to 14 days after clinical improvement
• Daily suppressive therapy for the remainder of pregnancy
Medications
• Adjust antibiotics based on culture/sensitivity results.
• ASB or UTI
• Macrobid 100 mg PO bid
Avoid if past medical history of G6PD deficiency to avoid hemolytic crisis.
• Bactrim DS one tab PO bid
Avoid in first trimester as trimethoprim is an antifolate agent with theoretical risk of neural tube defects.
Avoid in the third trimester due to risk of kernicterus.
• Amoxicillin 500 mg PO tid
• Ampicillin 250 mg PO qid
• Keflex 500 mg PO qid
• Pyelonephritis
• Intravenous antibiotics
Ampicillin 2 g every 6 hours plus gentamicin with dose dependent on selection of daily versus three times daily dosing regimen
Cefazolin 2 g every 8 hours
Ceftriaxone 1 g every 24 hours
• Oral antibiotics to complete course of treatment
Selection based on sensitivities.
Avoid nitrofurantoin (Macrobid) for completion of antibiotic regimen due to poor tissue penetration.
• Antibiotic suppression with Macrobid 100 mg PO qd for remainder of pregnancy to prevent recurrent UTIs or pyelonephritis (10)
Complications
• Sepsis requiring intensive care unit (ICU) admission
• Perinephric abscess
• Adult respiratory distress syndrome
• Preterm labor
• Preterm delivery
• Recurrent infections
URINARY CALCULI
Background
Definition
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