Symptoms may arise from pressure exerted within the overdistended uterus and upon adjacent organs. When distention is excessive, such as that shown in Figure 11-2, the mother may sufer dyspnea and orthopnea to such a degree that she may be able to breathe comfortably only when upright. Edema may develop as a consequence of major venous system compression by the enlarged uterus, and it tends to be most pronounced in the lower extremities, vulva, and abdominal wall. Rarely, oliguria may result from ureteral obstruction by the enlarged uterus (Chap. 53, p. 1037). Maternal complications such as these are typically associated with severe hydramnios from an underlying etiology.
Maternal complications associated with hydramnios include placental abruption, uterine dysfunction during labor, and postpartum hemorrhage. Placental abruption is fortunately infrequent. It may result from the rapid decompression of an overdistended uterus that follows fetal-membrane rupture or therapeutic amnioreduction. With prematurely ruptured membranes, a placental abruption occasionally occurs days or weeks after amniorrhexis. Uterine dysfunction consequent to overdistention may lead to postpartum atony and, in turn, postpartum hemorrhage.
Some outcomes more common with hydramnios include birthweight >4000 g, cesarean delivery, and importantly, perinatal mortality. Pregnancies with idiopathic hydramnios are associated with birthweights exceeding 4000 g in nearly 25 percent of cases, and the likelihood appears to be greater if the hydramnios is moderate or severe (Luo, 2016; Odibo, 2016; Wiegand, 2016). A rationale for this association is that larger fetuses have higher urine output, by virtue of their increased volume of distribution, and fetal urine is the largest contributor to amnionic luid volume. Cesarean delivery rates are also higher in pregnancies with idiopathic hydramnios, with reported rates of 35 to 55 percent (Dorleijn, 2009; Khan, 2017; Odibo, 2016).
An unresolved question is whether hydramnios alone raises the risk for perinatal mortality. Some studies have found no increase in stillbirth or neonatal death rates with idiopathic hydramnios, whereas others show a greater risk (Khan, 2017; Pilliod, 2015; Wiegand, 2016). Using birth certificate data from the state of California, Pilliod and coworkers (2015) identified hydramnios in 0.4 percent of singleton, nonanomalous pregnancies, and afected pregnancies had significantly greater stillbirth rates. At 37 weeks, the stillbirth risk was sevenfold higher in pregnancies with hydramnios. By 40 weeks, this risk was more than tenfold higher-66 per 10,000 births compared with 6 per 10,000 without hydramnios.
isks appear to be compounded when a growth-restricted fetus is identiied with hydramnios (Erez, 2005). The combination also has a recognized association with trisomy 18. When an underlying cause is identified, degree of hydramnios has been associated with likelihood of preterm delivery, smallfor-gestational age newborn, and perinatal mortality (Pri-Paz, 2012). However, idiopathic hydramnios is generally not associated with preterm birth (Magann, 2010; Many, 1995; PantingKemp, 1999).