Urologic Anatomic and Physiologic Changes during Pregnancy (4)
Increase in renal size (≈1cm); thought to be result of increased renal vascular and interstitial volume
Hydronephrosis from:
Obstructive effect of the enlarging uterus (likely main factor)
Progesterone mediated relaxation of smooth muscle of collecting system and bladder resulting in decreased collecting system and ureteral peristalsis, ureteral dilatation, increased bladder capacity
Bladder changes; enlarging uterus displaces bladder, progesterone stimulates relaxation resulting in increased capacity; estrogen may cause bladder hypertrophy
Improved renal function; glomerular filtration increases by 30-50%, and urinary protein excretion increases; values considered normal in non-pregnant females may represent renal insufficiency during pregnancy. Similarly, urinary protein in pregnancy is not considered abnormal until > 300 mg of protein in 24 hours is excreted
Changes to the urinary tract in pregnancy that increase risk of UTI:
Decreased bladder tone because of edema and hyperemia
Increased urine volume in the upper collecting system as the physiologic dilation of pregnancy evolves, can increase the propensity to develop pyelonephritis
Complications associated with bacteruria during pregnancy
Pyelonephritis
Prematurity and prenatal mortality
Maternal anemia (conflicting evidence)
Recurrent UTIs are not a contraindication to pregnancy
Pregnancy in women with renal insufficiency
The degree of renal function impairment is the major determinant for pregnancy outcome
Fetal survivors of pregnant women with mild or moderate renal disease is only slightly diminished.
However, the perinatal mortality is approximately 4x higher with severe disease
One of the most common infections encountered during pregnancy.
Prevalence of bacteriuria in pregnant females varies from 4-7%
Prevalence of asymptomatic bacteriuria in pregnancy is similar to that of the general population
More likely to progress to pyelonephritis
Spontaneous resolution of asymptomatic bacteriuria in pregnant females is unlikely unless treated, unlike non-pregnant females who often clear their asymptomatic bacteriuria
Labs: initial screening culture (significant false-negative rates with urinalysis or reagent strip testing) should be performed in all pregnant women during the first trimester
If the culture shows no growth, repeat cultures are generally unnecessary because patients who have no growth in their urine early in their pregnancy are unlikely to develop bacteriuria later
Fluoroquinolones: risk of damage to immature cartilage
Trimethroprim: risk of megaloblastic anemia because of anti-folic acid action
TMP/SMX: early, risk of teratogenicity; late, risk of kernicterus
Nitrofurantoin: avoid during 3rd trimester due to risk of hemolytic anemia
Chloramphenicol: risk of “gray baby” syndrome
Erythromycin: risk of maternal cholestatic jaundice
Tetracyclines: risk acute liver decompensation in the mother and inhibition of new bone growth in the fetus
Follow-up cultures should be obtained to document absence of infection.
If the culture is positive, the cause of bacteriuria must be determined to be lack of resolution, bacterial persistence, or reinfection.
If the infection is unresolved, proper selection and administration of another drug probably will solve the problem.
If the problem is bacterial persistence or rapid reinfection, antimicrobial suppression of infection or prophylaxis throughout the remainder of the pregnancy should be considered.
If a pregnant female has a single episode of pyelonephritis or two episodes of cystitis, daily suppression with either nitrofurantoin or cephalexin should be considered until delivery.