Perhaps half of women with reflux nephropathy were treated during childhood for renal infections. Many also had surgical correction of reflux as children, and these women commonly have bacteriuria when pregnant (Mor, 2003). In the other half of women with relux nephropathy, a clear history of recurrent cystitis, acute pyelonephritis, or obstructive disease is lacking. Reports describing 939 pregnancies in 379 women with reflux nephropathy indicate that impaired renal function and bilateral renal scarring were associated with increased maternal complications (EI-Khatib, 1994; Jungers, 1996; Kohler, 2003). Chronic renal disease and pregnancy outcome are discussed on page 1034.
Kidney stones develop in up to 9 percent of women during their lifetime with an average age of onset in the third decade (Curhan, 2015). Calcium salts make up approximately 90 percent of stones, and hyperparathyroidism should be excluded. Although calcium oxalate stones in young nonpregnant women are most common, most stones in pregnancy-65 to 75 percent-are calcium phosphate or hydroxyapatite (Ross, 2008; Tan, 2013). Patients who have a stone typically form another one every 2 to 3 years. One study found pregnancy was a risk factor for stone formation (Reinstatler, 2017).
Contrary to past teachings, a low-calcium diet promotes stone formation. Thiazide diuretics diminish stone formation. In general, obstruction, infection, intractable pain, and heavy bleeding are indications for stone removal, discussed later.
he incidence of stone disease complicating pregnancy varies. At the low end, the incidence was 0.3 admissions per 1000 pregnancies at Parkland Hospital (Butler, 2000). In an Israeli study, the incidence in nearly 220,000 pregnancies was 0.8 per 1000 (Rosenberg, 2011). In Washington state, the incidence was 1.7 per 1000 pregnancies (Swartz, 2007). Bladder stones are rare, but recurrent infection and labor obstructed by stones have been reported (Ait Benkaddour, 2006; Ruan, 2011).
Data are conflicting whether women with kidney stones have an increased risk for low-birthweight and preterm newborns. In one study of 2239 women with nephrolithiasis compared with normal controls, stones were associated with a signiicantly elevated preterm delivery rate-l0.6 versus 6.4 percent (Swartz, 2007). The more recent nationwide study from Taiwan also found 20-to 40-percent increases in rates of low birthweight and pre term birth (Chung, 2013). In contrast, a study from Hungary reported that pregnancy outcomes, including preterm delivery, were similar in women with stones and normal controls (Banhidy, 2007). Comparable conclusions were drawn from the Israeli study discussed above (Rosenberg, 2011).
Pregnant women may have fewer symptoms with stone passage because of urinary tract dilatation (Hendricks, 1991; Tan, 2013). hat said, more than 90 percent of pregnant women with symptomatic nephrolithiasis present with pain.