Editing Stones During Pregnancy

== Epidemiology ==

* '''<span style="color:#ff0000">Overall, no difference in the incidence of symptomatic urinary calculi for pregnant women compared to nonpregnant women''' of childbearing age

== Urologic Changes in Pregnancy ==

# '''<span style="color:#ff0000">Increased renal blood flow, resulting in (4):'''
## '''<span style="color:#ff0000">Increased glomerular filtration rate''' (by 30-50%) and correspond decrease in serum creatinine and blood urea nitrogen
##*'''<span style="color:#ff0000">Normal ranges of serum creatinine and blood urea nitrogen are ≈25% lower for the pregnant patient'''
## '''<span style="color:#ff0000">Increased filtered loads of sodium, calcium, and uric acid''', causing potentially lithogenic changes of hypercalciuria and hyperuricosuria
##*'''Hypercalciuria is further enhanced by placental production of 1,25(OH)2D3, which increases intestinal calcium absorption and secondarily suppresses PTH'''
##*'''These metabolic alterations in the urine may contribute to the accelerated encrustation of ureteral stents during pregnancy'''
##** As a result of these temporary physiologic changes, a metabolic evaluation is not generally undertaken to determine the cause of the stone disease until after the woman has delivered and returned to her baseline state of health.
##'''<span style="color:#ff0000">Increased filtered loads of urinary inhibitors, such as citrate and magnesium'''
##'''<span style="color:#ff0000">Increased urine output'''
# '''<span style="color:#ff0000">Hydronephrosis/hydroureter of Pregnancy'''
#* '''<span style="color:#ff0000">Due to (2):'''
#*# '''<span style="color:#ff0000">Increased circulating progesterone</span>''', which causes relaxation of ureteral smooth muscle, reducing ureteral peristalsis.
#*# '''<span style="color:#ff0000">Direct compression of the ureters by the gravid uterus'''
#*#* '''Likely the main factor'''
#*#** Women with an altered upper urinary tract in whom the ureter does not cross the pelvic brim, such as those with ileal conduit or renal ectopia, do not experience hydronephrosis during pregnancy
#* '''Right ureter tends to be more dilated than the left'''
#* '''Resolves 4-6 weeks post-partum'''
#'''Stone composition'''
#* A multi-institutional study found that '''74% of stones from pregnant women were composed predominantly of calcium phosphate''' and 26% were predominantly calcium oxalate

== Natural History ==

* '''<span style="color:#ff0000">Renal colic during pregnancy is a risk for:'''
*# '''<span style="color:#ff0000">Preterm delivery'''
*# '''<span style="color:#ff0000">Premature rupture of membranes'''

== Diagnosis and evaluation ==

=== History and Physical Exam ===

* '''<span style="color:#ff0000">History'''
**'''<span style="color:#ff0000">Signs and Symptoms'''
***'''<span style="color:#ff0000">Most common presenting symptoms: flank pain''' 
***'''<span style="color:#ff0000">Usually accompanied by either macroscopic or microscopic hematuria'''
*** '''Many of the usual manifesting signs and symptoms may be masked by the patient’s gravid status'''

=== Imaging ===

==== Ultrasound ====
* '''<span style="color:#ff0000">Preferred modality in pregnant women'''
* '''<span style="color:#ff0000">If an obstructing calculus cannot be visualized by conventional renal US, transvaginal US can provide imaging of the distal ureter'''

==== MRI ====
* '''<span style="color:#ff0000">Recommended as a second-line imaging test when ultrasonography is nondiagnostic''' (CW12 p2039)
* Does not rely on ionizing radiation or contrast medium, making it a potentially attractive tool to evaluate pregnant patients.
* '''Because MRI does not visualize calcium, stones are seen as filling defects overlying the high signal intensity of urine.'''
* '''Visualization of smaller stones with this technique is difficult'''

==== Limited Intravenous Pyelography (IVP) ====
* '''Consists of one scout image followed by one plate taken ≈30 minutes after the injection of contrast.'''
** '''Each plain film exposes the fetus to 0.1-0.2 rads''', much below the threshold of 1.2 rads, at which the risk begins to increase.
*** '''Low-dose CT <0.19 rads''' (1.9 mSV; 1 rad = 10 mSV) (online source)
*** '''The total pregnancy exposure should not exceed the American College of Obstetrics and Gynecology (ACOG) recommended maximum of 5 rads''' (2016 AUA Stone Surgery Guidelines)

==== CT ====

*'''Low-dose CT'''
* '''Conventional CT'''
** '''Should be avoided''' during pregnancy due radiation particularly high dose
**

== Management ==

=== Options ===
*'''<span style="color:#ff0000">First-line: observation</span>'''
*'''<span style="color:#ff0000">Second-line: intervention</span>'''
**'''<span style="color:#ff0000">Pharmacological (1):</span>''' 
**#'''<span style="color:#ff0000">Medical expulsive therapy (MET)</span>'''
**'''<span style="color:#ff0000">Surgical (2):</span>''' 
**#'''<span style="color:#ff0000">Ureteral stent or percutaneous nephrostomy tube</span>'''
**#'''<span style="color:#ff0000">Ureteroscopy</span>'''

==== Observation (first-line) ====
*'''<span style="color:#ff0000">Observation is the first-line management strategy in pregnant patients and well controlled symptoms</span>'''
**50-80% of pregnant patients with symptomatic calculi will pass their stones spontaneously
**A stone event in pregnancy is associated with an increased risk of maternal and fetal morbidity, so patients should be followed closely for recurrent or persistent symptoms.

==== Intervention (second-line) ====
*'''<span style="color:#ff0000">Pharmacological and surgical intervention should be coordinated with the obstetrician</span>'''

===== Pharmacological</span> =====
*'''<span style="color:#ff0000">Should MET be considered for the pregnant patient, patient should be counseled that MET has not been investigated in the pregnant population, and the medication is being used for an “off-label” purpose.</span>'''
*'''<span style="color:#ff0000">NSAIDs (e.g., ketorolac) are contraindicated in pregnancy</span>'''

===== Surgical</span> =====
* '''<span style="color:#ff0000">Ureteral stent or percutaneous nephrostomy tube</span>'''
** <span style="color:#ff0000">'''Disadvantages''':</span>
**# '''<span style="color:#ff0000">Increased risk of stent encrustation/migration</span>'''
**#* '''<span style="color:#ff0000">Ureteral stents placed in pregnant women should be exchanged every 4 to 6 weeks.</span>'''
**#** For a woman in an early gestational stage, multiple stent changes will be required over the course of the pregnancy.
**# '''Increased risk for bacteriuria and UTI'''
**# '''Stent pain, which can have a negative impact on a patient’s quality of life'''
*** Many of the same limitations that apply to ureteral stents also apply to nephrostomy tubes in that ≈50% of patients will require exchanges, replacements, or flushing because of dislodgement or obstruction
* '''<span style="color:#ff0000">Ureteroscopy</span>'''
** '''<span style="color:#ff0000">Methods to minimize radiation exposure in a pregnant patient (4):</span>'''
**# '''<span style="color:#ff0000">Low dosed and pulsed fluoroscopy</span>'''[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5851105/ §]
**# '''<span style="color:#ff0000">Collimating to the minimum required visual fluoroscopy field'''
**# '''<span style="color:#ff0000">Using the last image hold feature</span>'''
**#* Has been shown to reduce radiation exposure by reducing the number of repetitive images.
**# '''<span style="color:#ff0000">Below-table x-ray source</span>'''[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5851105/ §]
**#* The uterus is located superior and anterior aspect of the pelvis during the pregnancy
**#* X-ray beams that project in a posterior to anterior (PA) direction contribute to less radiation than the beam projected in anterior to posterior (AP) direction because, in PA projection, the X-ray gets attenuated before reaching anteriorly located uterus
**#** In the unpregnant- patient, '''positioning the radiation source of the C-arm under the operating table reduces exposure to the surgeon by reducing scatter radiation but does not change patient exposure.'''
**#*** '''Scattering of the primary beam from the patient is the primary source of radiation exposure to the operator during endourologic procedures.'''
**#**** Maximizing the distance between the operator and the patient during fluoroscopy is a very effective method of reducing exposure.
**# '''<span style="color:#ff0000">X-ray source further away from patient</span>'''
**#* '''Reduces exposure to fetus but increases scatter to physician'''
**# '''<span style="color:#ff0000">Lead apron placed below the patient's pelvis to shield the fetus</span>'''[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5851105/ §]
** '''American College of Obstetricians and Gynecologists (ACOG) guidelines recommend that <span style="color:#ff0000">any nonurgent surgeries, such as URS, should be performed in the second trimester of pregnancy</span> to minimize the risk of preterm contractions and spontaneous abortion[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5851105/ §]'''

== Questions ==

# What are potential risks of renal colic during pregnancy?
# What are the causes of physiologic hydronephrosis in pregnancy?
# If ureteroscopy is performed during pregnancy, what can be done to reduce radiation exposure to the fetus?

== Answers ==

# What are potential risks of renal colic during pregnancy?
## Premature delivery
## Premature rupture of membranes
# What are the causes of physiologic hydronephrosis in pregnancy?
## Compression by gravid ureters
## Increased progesterone
# If ureteroscopy is performed during pregnancy, what can be done to reduce radiation exposure to the fetus?
## Place x-ray source below patient
## Place lead apron below patient to protect fetus

== Next Chapter: [[Stones: Lower Urinary Tract Calculi|Lower Urinary Tract Calculi]] ==

== References ==

* Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 54