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Management of urinary calculi in pregnancy
MANAGEMENT
OF URINARY CALCULI
IN PREGNANCY JOSEPH
R. DRAGO, M.D.
THOMAS J. ROHNER, RONALD A. CHEZ,
JR., M.D.
M.D.
From the Departments of Surgery (Division of Urology) and Obstetrics and Gynecology, The Milton S. Hershey Medical Center, The Pennsylvania State University, Hershey, Pennsylvania
ABSTRACT - During the twenty-seven-month period ending April 1, 1982, 9 patients presented to the Milton S. Hershey Medical Center for evaluation and management of urinary calculi during pregnancy. During the same period, 1,696 deliveries were performed. This incidence of 11188 deliveries complicated by urinary calculi compares with previous series reporting an average incidence of approximately 1 11,500 deliveries. In this review, we discuss the management of and the need for surgical intervention of calculi during pregnancy.
Urinary calculi are considered relatively infrequent complications of pregnancy. The reported incidence averages approximately l/1,500 deliveries with a range of l/227 to l/3,821.‘-” During the last twenty-seven months at our institution, 1,696 deliveries were performed, and we cared for 9 pregnant women with urinary calculi. This is an incidence of stones of l/188 deliveries (Table I). This article, a retrospective analysis of their presentation and subsequent course, was prompted by this high incidence. Material and Methods Nine patients were the subject of this review. At least 12 stones were passed, with 1 patient passing at least three stones during her pregnancy. Seven patients had their initial attack of renal colic during the third trimester; 1 patient had the initial attack of renal colic during the second trimester and another during the first trimester of pregnancy (Table II). The age range of patients was from fourteen to thirty-one years, with a mean age of twenty-two years; the parity averaged 0.7 and the gravidity averaged 1.7.
578
These patients were all evaluated on an inpatient basis; thus, some patients who were treated as outpatients may not have been included in this review. Diagnosis Definitive diagnosis was made on the passage of the urinary calculus. All of our patients had flank pain, most had abdominal pain, all had either gross or microscopic hematuria, and 1 patient presented with urinary tract sepsis (Table TABLE I.
Stone incidence in pregnancy
Reference McVann4 Semmens’ Harris and Dunnihoo5 Strong et al. ’ Cumming and Taylor9 Jones et al. l1 Lattanzi and Cook” Drago et al. (1982)
Cases/Obstetric Admissions
Incidence
12145,852 912,037 19/11,977 14122,495 13121,277 20134,081 961138,296 911,696
113,821 11227 l/630 l/1,607 l/1,636 l/1,704 l/1,441 l/188
UROLOGY / DECEMBER 1932 / VOLUMEXX, NUMBER6
II.
TABLE
Gestation (Week)
Pregnant patients with stones: Milton S. Hershey Medical Center (January, 1980, to April, 1982)
Age (Yr.)
Grav./Para
21 33 33 7 30
22 22 17 22 25
2/l l/2 l/O 2/l l/O
3182 7181 11/81 8181 7181
6
30
25
2/l
4181
7 8 9
30 31 31
14 18 31
l/O l/O 4/l
l/81 1l/80 3182
Case*
*Case 5 passed
three
stones during
pregnancy
Date
Size (Mm) 4 2 4 5
8 6 2
TABLE
Nine pregnant women with stones: III. diagnostic symptoms and signs Rate of Occurrence (%)
Diagnostic Data SYMPTOMS
100 67 56 78 67 33 22
Flank pain Premature labor Abdominal pain Urgency Dysuria Nausea and vomiting Gross hematuria Chills Fever
11
22
SIGNS
Costovertebral angle pain and/or tenderness Abdominal tenderness Pyuria greater than 7 WBClhpf Microhematuria
UROLOGY
/ DECEMBER
1982
100
/
Right ureteral calculus Right ureteral calculus Right ureteral calculus Left ureteral calculus Right multiple calculi Right multiple renal calculi with renal abscess Right ureteral calculus Left ureteral calculus Right ureteral calculus
and Case 2 two stones: total number
III). The location of the renal calculi was in the mid or distal ureter in 8 patients. One woman had multiple stones in the renal pelvis causing nonfunction, obstruction, pyohydronephrosis, and septicemia. A prior history of stone disease was obtained in 2 patients. Documented urinary tract infection was observed in 2 of these patients, with Escherichia coli as the organism. There were no abnormalities suggesting primary hyperparathyroidism when metabolic evaluation was performed. However, in 1 patient idiopathic hypercalciuria was diagnosed postpartum; this patient had 380 mg of calcium per twenty-four hours.
Management
Stone Location
of stones passed
Spontaneously passed Spontaneously passed Spontaneously passed Spontaneously passed Right double “J” ureteral stent Right nephrectomy Right ureter-al lithotomy Spontaneously passed Spontaneously passed was twelve
The major complication of pregnancy was the association of premature onset of labor in 6 of these 9 patients. In 2 patients, this was the presenting complaint with pain having a less significant role. The other 4 patients had pain perceived as equally important to the premature labor; in 3, primary medical attention was focused on the premature labor and its treatment. The presence of renal colic became more prominent only after the premature labor was being controlled with tocolysis. There was one stillborn birth. This occurred in a patient with multiple parasitic diseases and tuberculosis and was related to maternal debilitation rather than pathology associated with the renal calculus per se. In all patients, the relief of renal colic, with usually the passage of a stone, was associated with cessation of premature labor. However, it should be noted that all the patients in premature labor also received the beta agonist, terbutaline, for tocolysis. Three of these 9 patients who presented with ureteral calculi during pregnancy required urologic intervention. As mentioned, 1 patient had passed multiple stones, at least three of which were recovered during pregnancy and several of which were not. Surgical management consisted of ureteral lithotomy; nephrectomy in the patient who presented with septicemia, nonfunctioning kidney and pyohydronephrosis; and the use of a double “J” stent. No patient during or after surgical intervention had an associated premature labor.
67
Comment
56 89
Despite the fact that recent reviews of urinary calculi in pregnancy indicate a much lower incidence (l/1,500) th an this current series (l/188),
VOLUMEXX,NUMBER6
579
this review and past reviews do concur in that most patients (at least 50%) can be managed with conservative therapy of hydration and analgesics, and that most patients will pass their stones spontaneously. This is no different from management of nonpregnant patients with ureteral calculi as the presenting diagnosis. However, in patients in whom surgical intervention is required for either evaluation or treatment of high-grade renal obstruction or renal sepsis that may endanger fetal health, standard surgical procedures may be performed safely. Close monitoring of fetus and mother, careful attention toward fluid and electrolyte balance, and appropriate antibiotic coverage are all essential. Recent radiologic advances as well as technologic advances of new ureteral catheters potentially make the management of these patients less complicated. The use of a double “J” Cook catheter” does have some advantages in the management of patients with distal or proximal ureteral calculi that are causing symptoms necessitating relief of obstruction or relief of sepsis. These catheters technically can be placed primarily during the first or second trimester of pregnancy. At this time, the enlarging uterus has not greatly compromised the ureters, and both the anatomy of the pelvis and of the bladder are relatively normal. These catheters have the advantage of being soft and can be left in place for relatively long periods of time of up to six or nine months with few urologic complications. However, in the third trimester of pregnancy, when the uterus impacts on the pelvic brim and the pelvic floor anatomy is distorted, it may be very difficult to place one of these catheters, thus making their usage less appealing. However, it is in this latter group of patients that direct surgical intervention can be performed. This is especially so in patients with midureteral or upper ureteral calculi. In patients in whom premature delivery precipitated by the use of anesthetics or the trauma of surgery would result in an immature fetus with poor outcome, the use of percutaneous nephrostomy may be preferred treatment to: (1) relieve the obstruction; (2) allow renal drainage; and (3) protect both the fetus and the mother. These procedures have been done commonly at our institution for relief of obstruction in nonpregnant patients. They are a suitable alternative in those patients in whom endoscopic manipulation of ureteral catheters is technically impossible or in whom the risk of anesthesia is prohibitive. Thus
580
far, we have not had occasion to use these catheters in pregnant patients. The etiology of urinary calculi in pregnancy has been reviewed recently by Coe, Parks, and Lindheimer.3 In their series, 42 per cent of the women had idiopathic hypercalciuria, 13 per cent hyperuricosuria, 10 per cent primary hyperparathyroidism, 13 per cent infected stones, 3 per cent cystinuria, and 19 per cent idiopathic lithiasis. This is not significantly different from the etiology of stones in patients in general. In their review, pregnancy did not appear to exert any effect on stone disease; the number of stone epidsodes during pregnancy was close to that predicted from the patient years at risk and was similar to the rate of stone occurrence observed in their population of unselected nonpregnant patients. The diagnosis of urinary calculi during pregnancy can be made in a manner similar to that of urinary calculi presenting in the nonpregnant patient. Commonly, patients complain of renal colic as well as abdominal pain. There is also a high percentage of patients with a chief complaint of dysuria and urgency, especially in patients in whom the calculi is in the distal ureter near the ureterovesical junction. When a patient presents with renal colic, we obtain a twoexposure limited intravenous pyelogram. This is a flat plate followed by a thirty to sixty-minute postinjection film. We hope to find urinary columnation of contrast material down to the point of obstruction. If on this first film we are unable to identify that, we will take one additional x-ray film. The time interval depends on the degree of contrast material present in the obstructed kidney. If there is a fair amount of contrast material in the cortex and the renal pelvis, a film is taken in another hour and a half after the last film. If the nephrogram at this point is very faint, a film three hours after the first film will be taken. If the latter is unsuccessful in delineating the area of obstruction, another film an additional three hours later might be taken. Generally, the latter instance reflects high-grade obstruction, and this patient most likely would undergo attempts at endoscopic evaluation and either passage of a catheter or extraction of a stone. This latter approach is always used if the patient is septic or if longstanding pyrexia has put the fetus at risk. Our experience and that of others indicates that women during their second and third trimesters can be treated appropriately surgically with a low risk of either maternal or fetal morbidity. In patients in their third trimester near term,
UROLOGY
/
DECEMBER
1932
/
VOLUME
XX. NUMBER
6
the maturity of the fetal lungs, as measured with the use of laboratory tests such as the LS ratio, may be helpful in determing the type and timing of the procedure. Examples of this are when it is anticipated that premature labor may occur subsequent to surgery for the relief of ureteral obstruction secondary to a large ureteral calculus that is deemed unlikely to pass spontaneously, or in a case in which the patient is having recurrent symptomatic urinary tract infections associated with sepsis. We do not have an explanation why urinary calculi appear in such high frequency in our pregnant population. Our evaluation does not indicate a higher number of patients presenting with infected stones, congenital abnormalities, or inherited metabolic diseases such as renal tubular acidosis. South Central Pennsylvania is not considered to be part of the stone belt. One explanation is that a high index of suspicion results in our making the diagnosis more frequently. Another explanation may reflect a recruitment of patients who are at high risk for pregnancy complications in general. However, 5 of the 9 patients were in our prenatal clinic when colic occurred; only 4 were referred. It is pertinent to note that 3 of these 4 patients were referred for premature labor, not because of colic and urinary calculi. Moreover, many of the other reviews were done from large referral centers similar to ours, a fact that diminishes the reason for the discrepancy in our incidence. In summary, the approach to diagnosis and various management plans have been outlined.
UROLOGY
/
DECEMBER
1982
/
VOLUME XX, NUMBER 6
Surgical intervention is required in less than 50 per cent of patients presenting with urinary calculi, and 50 per cent or greater of these patients presenting with urinary calculi during pregnancy will pass their stones spontaneously. With appropriate management including fluid and electrolytes and careful postdiagnostic management, these patients should be able to carry to term and deliver a viable fetus. Hershey, Pennsylvania 17033 (DR. DRAGO) References 1. Semmens JP: Major urologic complications in pregnancy, Obstet Gynecol 23: 561 (1964). 2. Sabin M, Parliament D, and Strean G: A ten year review of renal diseases in pregnancy, Canad Med Assoc J 83: 372 (1966). 3. Coe FL, Parks JH, and Lindheimer MD: Nephrolithiasis during pregnancy, N Engl J Med 298: 324 (1978). 4. McVann RM: Urinary calculi associated with pregnancy, Am J Obstet Gynecol 89: 314 (1964). 5. Harris RE, and Dunnihoo DR: Incidence and significance of urinary calculi and pregnancy, ibid 99: 237 (1967). 6. Harrow BR: Renal and ureteral calculi in pregnancy, Ob/Gyn Digest 9: 41 (1968). 7. Wogeski A, and Zajaczkowskt T: Urolithiasis and pregnancy, Ginec Pol 41: 287 (1970). 8. Strong DW, Murchison RJ, and Lynch DF: Management of ureteral calculi during pregnancy, Surg Gynecol Obstet 146: 694 (1978). 9. Cumming D, and Taylor PJ: Urologic and obstetric significance of urinary calculi in pregnancy, Obstet Gynecol 53: 595 (1979). 10. Lattanzi DR, and Cook WA: Urinary calculi in pregnancy, ibid 56: 462 (1980). 11. Jones WA, Correa RJ, and Ansell J: Urolithiasis associated with oreenancv, I Urol 122: 333 (1979). 12.* Fmney ‘&: Double-J and diversion stents, Urol Clin North Am 9: 1 (1982).
581
OF URINARY CALCULI
IN PREGNANCY JOSEPH
R. DRAGO, M.D.
THOMAS J. ROHNER, RONALD A. CHEZ,
JR., M.D.
M.D.
From the Departments of Surgery (Division of Urology) and Obstetrics and Gynecology, The Milton S. Hershey Medical Center, The Pennsylvania State University, Hershey, Pennsylvania
ABSTRACT - During the twenty-seven-month period ending April 1, 1982, 9 patients presented to the Milton S. Hershey Medical Center for evaluation and management of urinary calculi during pregnancy. During the same period, 1,696 deliveries were performed. This incidence of 11188 deliveries complicated by urinary calculi compares with previous series reporting an average incidence of approximately 1 11,500 deliveries. In this review, we discuss the management of and the need for surgical intervention of calculi during pregnancy.
Urinary calculi are considered relatively infrequent complications of pregnancy. The reported incidence averages approximately l/1,500 deliveries with a range of l/227 to l/3,821.‘-” During the last twenty-seven months at our institution, 1,696 deliveries were performed, and we cared for 9 pregnant women with urinary calculi. This is an incidence of stones of l/188 deliveries (Table I). This article, a retrospective analysis of their presentation and subsequent course, was prompted by this high incidence. Material and Methods Nine patients were the subject of this review. At least 12 stones were passed, with 1 patient passing at least three stones during her pregnancy. Seven patients had their initial attack of renal colic during the third trimester; 1 patient had the initial attack of renal colic during the second trimester and another during the first trimester of pregnancy (Table II). The age range of patients was from fourteen to thirty-one years, with a mean age of twenty-two years; the parity averaged 0.7 and the gravidity averaged 1.7.
578
These patients were all evaluated on an inpatient basis; thus, some patients who were treated as outpatients may not have been included in this review. Diagnosis Definitive diagnosis was made on the passage of the urinary calculus. All of our patients had flank pain, most had abdominal pain, all had either gross or microscopic hematuria, and 1 patient presented with urinary tract sepsis (Table TABLE I.
Stone incidence in pregnancy
Reference McVann4 Semmens’ Harris and Dunnihoo5 Strong et al. ’ Cumming and Taylor9 Jones et al. l1 Lattanzi and Cook” Drago et al. (1982)
Cases/Obstetric Admissions
Incidence
12145,852 912,037 19/11,977 14122,495 13121,277 20134,081 961138,296 911,696
113,821 11227 l/630 l/1,607 l/1,636 l/1,704 l/1,441 l/188
UROLOGY / DECEMBER 1932 / VOLUMEXX, NUMBER6
II.
TABLE
Gestation (Week)
Pregnant patients with stones: Milton S. Hershey Medical Center (January, 1980, to April, 1982)
Age (Yr.)
Grav./Para
21 33 33 7 30
22 22 17 22 25
2/l l/2 l/O 2/l l/O
3182 7181 11/81 8181 7181
6
30
25
2/l
4181
7 8 9
30 31 31
14 18 31
l/O l/O 4/l
l/81 1l/80 3182
Case*
*Case 5 passed
three
stones during
pregnancy
Date
Size (Mm) 4 2 4 5
8 6 2
TABLE
Nine pregnant women with stones: III. diagnostic symptoms and signs Rate of Occurrence (%)
Diagnostic Data SYMPTOMS
100 67 56 78 67 33 22
Flank pain Premature labor Abdominal pain Urgency Dysuria Nausea and vomiting Gross hematuria Chills Fever
11
22
SIGNS
Costovertebral angle pain and/or tenderness Abdominal tenderness Pyuria greater than 7 WBClhpf Microhematuria
UROLOGY
/ DECEMBER
1982
100
/
Right ureteral calculus Right ureteral calculus Right ureteral calculus Left ureteral calculus Right multiple calculi Right multiple renal calculi with renal abscess Right ureteral calculus Left ureteral calculus Right ureteral calculus
and Case 2 two stones: total number
III). The location of the renal calculi was in the mid or distal ureter in 8 patients. One woman had multiple stones in the renal pelvis causing nonfunction, obstruction, pyohydronephrosis, and septicemia. A prior history of stone disease was obtained in 2 patients. Documented urinary tract infection was observed in 2 of these patients, with Escherichia coli as the organism. There were no abnormalities suggesting primary hyperparathyroidism when metabolic evaluation was performed. However, in 1 patient idiopathic hypercalciuria was diagnosed postpartum; this patient had 380 mg of calcium per twenty-four hours.
Management
Stone Location
of stones passed
Spontaneously passed Spontaneously passed Spontaneously passed Spontaneously passed Right double “J” ureteral stent Right nephrectomy Right ureter-al lithotomy Spontaneously passed Spontaneously passed was twelve
The major complication of pregnancy was the association of premature onset of labor in 6 of these 9 patients. In 2 patients, this was the presenting complaint with pain having a less significant role. The other 4 patients had pain perceived as equally important to the premature labor; in 3, primary medical attention was focused on the premature labor and its treatment. The presence of renal colic became more prominent only after the premature labor was being controlled with tocolysis. There was one stillborn birth. This occurred in a patient with multiple parasitic diseases and tuberculosis and was related to maternal debilitation rather than pathology associated with the renal calculus per se. In all patients, the relief of renal colic, with usually the passage of a stone, was associated with cessation of premature labor. However, it should be noted that all the patients in premature labor also received the beta agonist, terbutaline, for tocolysis. Three of these 9 patients who presented with ureteral calculi during pregnancy required urologic intervention. As mentioned, 1 patient had passed multiple stones, at least three of which were recovered during pregnancy and several of which were not. Surgical management consisted of ureteral lithotomy; nephrectomy in the patient who presented with septicemia, nonfunctioning kidney and pyohydronephrosis; and the use of a double “J” stent. No patient during or after surgical intervention had an associated premature labor.
67
Comment
56 89
Despite the fact that recent reviews of urinary calculi in pregnancy indicate a much lower incidence (l/1,500) th an this current series (l/188),
VOLUMEXX,NUMBER6
579
this review and past reviews do concur in that most patients (at least 50%) can be managed with conservative therapy of hydration and analgesics, and that most patients will pass their stones spontaneously. This is no different from management of nonpregnant patients with ureteral calculi as the presenting diagnosis. However, in patients in whom surgical intervention is required for either evaluation or treatment of high-grade renal obstruction or renal sepsis that may endanger fetal health, standard surgical procedures may be performed safely. Close monitoring of fetus and mother, careful attention toward fluid and electrolyte balance, and appropriate antibiotic coverage are all essential. Recent radiologic advances as well as technologic advances of new ureteral catheters potentially make the management of these patients less complicated. The use of a double “J” Cook catheter” does have some advantages in the management of patients with distal or proximal ureteral calculi that are causing symptoms necessitating relief of obstruction or relief of sepsis. These catheters technically can be placed primarily during the first or second trimester of pregnancy. At this time, the enlarging uterus has not greatly compromised the ureters, and both the anatomy of the pelvis and of the bladder are relatively normal. These catheters have the advantage of being soft and can be left in place for relatively long periods of time of up to six or nine months with few urologic complications. However, in the third trimester of pregnancy, when the uterus impacts on the pelvic brim and the pelvic floor anatomy is distorted, it may be very difficult to place one of these catheters, thus making their usage less appealing. However, it is in this latter group of patients that direct surgical intervention can be performed. This is especially so in patients with midureteral or upper ureteral calculi. In patients in whom premature delivery precipitated by the use of anesthetics or the trauma of surgery would result in an immature fetus with poor outcome, the use of percutaneous nephrostomy may be preferred treatment to: (1) relieve the obstruction; (2) allow renal drainage; and (3) protect both the fetus and the mother. These procedures have been done commonly at our institution for relief of obstruction in nonpregnant patients. They are a suitable alternative in those patients in whom endoscopic manipulation of ureteral catheters is technically impossible or in whom the risk of anesthesia is prohibitive. Thus
580
far, we have not had occasion to use these catheters in pregnant patients. The etiology of urinary calculi in pregnancy has been reviewed recently by Coe, Parks, and Lindheimer.3 In their series, 42 per cent of the women had idiopathic hypercalciuria, 13 per cent hyperuricosuria, 10 per cent primary hyperparathyroidism, 13 per cent infected stones, 3 per cent cystinuria, and 19 per cent idiopathic lithiasis. This is not significantly different from the etiology of stones in patients in general. In their review, pregnancy did not appear to exert any effect on stone disease; the number of stone epidsodes during pregnancy was close to that predicted from the patient years at risk and was similar to the rate of stone occurrence observed in their population of unselected nonpregnant patients. The diagnosis of urinary calculi during pregnancy can be made in a manner similar to that of urinary calculi presenting in the nonpregnant patient. Commonly, patients complain of renal colic as well as abdominal pain. There is also a high percentage of patients with a chief complaint of dysuria and urgency, especially in patients in whom the calculi is in the distal ureter near the ureterovesical junction. When a patient presents with renal colic, we obtain a twoexposure limited intravenous pyelogram. This is a flat plate followed by a thirty to sixty-minute postinjection film. We hope to find urinary columnation of contrast material down to the point of obstruction. If on this first film we are unable to identify that, we will take one additional x-ray film. The time interval depends on the degree of contrast material present in the obstructed kidney. If there is a fair amount of contrast material in the cortex and the renal pelvis, a film is taken in another hour and a half after the last film. If the nephrogram at this point is very faint, a film three hours after the first film will be taken. If the latter is unsuccessful in delineating the area of obstruction, another film an additional three hours later might be taken. Generally, the latter instance reflects high-grade obstruction, and this patient most likely would undergo attempts at endoscopic evaluation and either passage of a catheter or extraction of a stone. This latter approach is always used if the patient is septic or if longstanding pyrexia has put the fetus at risk. Our experience and that of others indicates that women during their second and third trimesters can be treated appropriately surgically with a low risk of either maternal or fetal morbidity. In patients in their third trimester near term,
UROLOGY
/
DECEMBER
1932
/
VOLUME
XX. NUMBER
6
the maturity of the fetal lungs, as measured with the use of laboratory tests such as the LS ratio, may be helpful in determing the type and timing of the procedure. Examples of this are when it is anticipated that premature labor may occur subsequent to surgery for the relief of ureteral obstruction secondary to a large ureteral calculus that is deemed unlikely to pass spontaneously, or in a case in which the patient is having recurrent symptomatic urinary tract infections associated with sepsis. We do not have an explanation why urinary calculi appear in such high frequency in our pregnant population. Our evaluation does not indicate a higher number of patients presenting with infected stones, congenital abnormalities, or inherited metabolic diseases such as renal tubular acidosis. South Central Pennsylvania is not considered to be part of the stone belt. One explanation is that a high index of suspicion results in our making the diagnosis more frequently. Another explanation may reflect a recruitment of patients who are at high risk for pregnancy complications in general. However, 5 of the 9 patients were in our prenatal clinic when colic occurred; only 4 were referred. It is pertinent to note that 3 of these 4 patients were referred for premature labor, not because of colic and urinary calculi. Moreover, many of the other reviews were done from large referral centers similar to ours, a fact that diminishes the reason for the discrepancy in our incidence. In summary, the approach to diagnosis and various management plans have been outlined.
UROLOGY
/
DECEMBER
1982
/
VOLUME XX, NUMBER 6
Surgical intervention is required in less than 50 per cent of patients presenting with urinary calculi, and 50 per cent or greater of these patients presenting with urinary calculi during pregnancy will pass their stones spontaneously. With appropriate management including fluid and electrolytes and careful postdiagnostic management, these patients should be able to carry to term and deliver a viable fetus. Hershey, Pennsylvania 17033 (DR. DRAGO) References 1. Semmens JP: Major urologic complications in pregnancy, Obstet Gynecol 23: 561 (1964). 2. Sabin M, Parliament D, and Strean G: A ten year review of renal diseases in pregnancy, Canad Med Assoc J 83: 372 (1966). 3. Coe FL, Parks JH, and Lindheimer MD: Nephrolithiasis during pregnancy, N Engl J Med 298: 324 (1978). 4. McVann RM: Urinary calculi associated with pregnancy, Am J Obstet Gynecol 89: 314 (1964). 5. Harris RE, and Dunnihoo DR: Incidence and significance of urinary calculi and pregnancy, ibid 99: 237 (1967). 6. Harrow BR: Renal and ureteral calculi in pregnancy, Ob/Gyn Digest 9: 41 (1968). 7. Wogeski A, and Zajaczkowskt T: Urolithiasis and pregnancy, Ginec Pol 41: 287 (1970). 8. Strong DW, Murchison RJ, and Lynch DF: Management of ureteral calculi during pregnancy, Surg Gynecol Obstet 146: 694 (1978). 9. Cumming D, and Taylor PJ: Urologic and obstetric significance of urinary calculi in pregnancy, Obstet Gynecol 53: 595 (1979). 10. Lattanzi DR, and Cook WA: Urinary calculi in pregnancy, ibid 56: 462 (1980). 11. Jones WA, Correa RJ, and Ansell J: Urolithiasis associated with oreenancv, I Urol 122: 333 (1979). 12.* Fmney ‘&: Double-J and diversion stents, Urol Clin North Am 9: 1 (1982).
581