Relaxation of ureteral smooth muscle, mediated in part by the effects of prostaglandins as well as the exertion of pressure on the ureters by the enlarged uterus, typically causes some dilatation of the calyceal system during normal gestation. This so-called functional hydronephrosis can be detected by renal ultrasonography and is not diagnostic of urinary tract obstruction as the cause of renal failure in this setting. In rare instances, however, the uterus during pregnancy may cause sufficient obstruction to produce a reduction in the glomerular filtration rate. Normalization of renal function when the patient is in the lateral recumbent position and its recurrence when the patient is supine should suggest the possibility of this diagnosis. In patients with severe preeclampsia or eclampsia, maternal mortality is increased, primarily because of intracerebral hemorrhage.
Definitive therapy requires delivery of the fetus and placenta.
The only reason to delay delivery in a patient with established preeclampsia is evidence of fetal immaturity. Isolated mild hypertension that develops during the third trimester does not usually necessitate immediate delivery. Although the minimum level of blood pressure elevation that will injure the fetus is unknown, an adverse outcome from mild hypertension is uncommon in patients who do not develop preeclampsia. Data on the treatment of chronic hypertension during pregnancy are incomplete. A substantial drop in maternal blood pressure with therapy could impair uteroplacental blood flow, thereby compromising fetal survival.