Diagnosis:
The classic clinical presentation of placenta previa is painless bleeding in the late second trimester or early third trimester. However, some patients with placenta previa will experience painful bleeding, possibly the consequence of uterine contractions or placental separation, whereas others will experience no bleeding at all before labor. Placenta previa may also lead to an unstable lie or malpresentation in late pregnancy. The majority of cases of placenta previa are diagnosed during routine sonography in asymptomatic women, usually during the second trimester. The initial episode of bleeding has a peak incidence at about the 34th week of pregnancy, although one-third of cases become symptomatic before the 30th week and one-third after the 36th week. Absence of bleeding prior to term does not rule out placenta previa. In approximately 10% of cases, bleeding begins only with the onset of labor, and in these situations one is more likely to find a partial or marginal placenta previa, or a low-lying placenta. Although transabdominal sonography is frequently used for placental location, this technique lacks some precision in diagnosing placenta previa. Numerous studies have demonstrated the accuracy of transvaginal sonography for the diagnosis of placenta previa, uniformly finding that transvaginal sonography is superior to transabdominal sonography for this finding. False-positive and --negative rates for the diagnosis of placenta previa using transabdominal sonography range from 2% to 25%.
Diagnosis:
The classic clinical presentation of placenta previa is painless bleeding in the late second trimester or early third trimester. However, some patients with placenta previa will experience painful bleeding, possibly the consequence of uterine contractions or placental separation, whereas others will experience no bleeding at all before labor. Placenta previa may also lead to an unstable lie or malpresentation in late pregnancy. The majority of cases of placenta previa are diagnosed during routine sonography in asymptomatic women, usually during the second trimester. The initial episode of bleeding has a peak incidence at about the 34th week of pregnancy, although one-third of cases become symptomatic before the 30th week and one-third after the 36th week. Absence of bleeding prior to term does not rule out placenta previa. In approximately 10% of cases, bleeding begins only with the onset of labor, and in these situations one is more likely to find a partial or marginal placenta previa, or a low-lying placenta. Although transabdominal sonography is frequently used for placental location, this technique lacks some precision in diagnosing placenta previa. Numerous studies have demonstrated the accuracy of transvaginal sonography for the diagnosis of placenta previa, uniformly finding that transvaginal sonography is superior to transabdominal sonography for this finding. False-positive and --negative rates for the diagnosis of placenta previa using transabdominal sonography range from 2% to 25%.
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