The epidemiology and clinical history of asymptomatic midtrimester placenta previa.

The current case-controlled study examines the epidemiologic factors and subsequent clinical history in 139 patients with asymptomatic low placentation and 137 patients with normal placental position diagnosed in the second and third trimesters by gray-scale ultrasonography. Increased maternal age or parity and previous endometrial or myometrial damage were significantly associated with asymptomatic midtrimester low implantation. Three percent of early low implantations persisted as instances of placenta previa at term. However, in low implantation, the antepartum course was associated with perinatal complications in 45% of patients. Statistically significant increases in third-trimester bleeding, abruptio placentae, and suspected intrauterine growth retardation were shown in the patients with low implantation, when compared to the control patients. Forty-two percent of the patients with low implantation were delivered by cesarean section. The need for cesarean delivery, loss of blood, and prolonged hospitalization were statistically increased in the patients with low implantation. Infants born to mothers with low implantation showed statistically significant increases in prematurity, low birth weight, and perinatal mortality when compared to infants born to control patients.