he 24-hour urine collection is afected by urinaty tract dilatation, which is discussed in the next section. he dilated tract may lead to errors related both to retention-hundreds of milliliters of urine remaining in the dilated tract-and to timing-the remaining urine may have formed hours before the collection. To minimize these pitfalls, the patient is irst hydrated and positioned in lateral recumbency-the deinitive nonobstructive posture-for 45 to 60 minutes. After this, she is asked to void, and this specimen is discarded. Immediately following this void, her 24-hour collection begins. During the final hour of collection, the patient is again placed in the lateral recumbent position. But, at the end of this hour, the inal collected urine is incorporated into the total collected volume (Lindheimer, 2010).
Last, the protein/creatinine ratio is a promising approach because data can be obtained quickly and collection errors are ,S 200 avoided. Disadvantageously, the amount of protein per unit of creatinine excreted during a 24-hour period is not constant, and the thresholds to deine abnormal vary. Nomograms for cated pregnancies have been developed (Waugh, 2003).
After the uterus completely rises out of the pelvis, it rests on the ureters. This laterally displaces and compresses them at the pelvic brim. Above this level, elevated intraureteral tonus results, and ureteral dilatation is impressive (Rubi, 1968). It is right sided in 86 percent of women (Fig. 4-15) (Schulman, 1975). This unequal dilatation may result from cushioning provided the left ureter by the sigmoid colon and perhaps from greater right ureteral compression exerted by the dextrorotated uterus. The right ovarian vein complex, which is remarkably dilated during pregnancy, lies obliquely over the right ureter and may also contribute to right ureteral dilatation.
Progesterone likely has some additional efect. Van Wagenen and Jenkins (1939) described continued ureteral dilatation after removal of the monkey fetus but with the placenta left in situ. The relatively abrupt onset of dilatation in women at midpregnancy, however, seems more consistent with ureteral compression.
Ureteral elongation accompanies distention, and the ureter is frequently thrown into curves of varying size, the smaller of which may be sharply angulated. hese so-called kinks are
FIGURE 4-15 Hydronephrosis. Plain film from the 15-minute image of an intravenous pyelogram (IVP). Moderate hydronephrosis on the right (arrows) and mild hydronephrosis on the left (arrowheads) are both normal for this 35-week gestation.
poorly named, because the term connotes obstruction. hey are usually single or double curves that, when viewed in a radiograph taken in the same plane as the curve, may appear as acute angulations. Another exposure at right angles nearly always identiies them to be gentle curves. Despite these anatomical changes, complication rates associated with ureteroscopy in pregnant and nonpregnant patients do not difer signiicantly (Semins, 2014).
he bladder shows few significant anatomical changes before 12 weeks' gestation. Subsequently, however, increased uterine size, the hyperemia that afects all pelvic organs, and hyperplasia of bladder muscle and connective tissues elevate the trigone and thicken its intraureteric margin. Continuation of this process to term produces marked deepening and widening of the trigone. The bladder mucosa is unchanged other than an increase in the size and tortuosity of its blood vessels.