Rizos N, Doran T A, Miskin M, Benzie R J, Ford J A
Am J Obstet Gynecol. 1979 Feb 1;133(3):287-91. doi: 10.1016/0002-9378(79)90680-x.
Placental localization by diagnostic ultrasound was performed at 16 to 18 weeks' gestation in 1,098 patients prior to amniocentesis for genetic indications. Placenta previa was diagnosed in 58 patients, 47 of whom went on to delivery uncomplicated by placenta previa. There were five patients with placenta previa at delivery, four of whom had third-trimester bleeding. One patient was diagnosed as having a normal placental implantation at midtrimester but placenta previa was demonstrated at delivery. The incidence of placenta previa at 16 to 18 weeks' was 5.3% and fell to 0.58% at delivery, indicating a 90% conversion rate. Thus the vast majority of cases of asymptomatic placenta previa remain so and convert before delivery. These patients should be observed with serial ultrasound at 6 to 8 week intervals until delivery or unequivocal conversion. No restriction in activity seems indicated unless the placenta previa persists beyond 30 weeks or becomes clinically manifest.
对1098例因遗传指征行羊膜腔穿刺术的孕妇，于妊娠16至18周时用诊断性超声进行胎盘定位。诊断为前置胎盘的有58例，其中47例顺利分娩，未因前置胎盘而出现并发症。分娩时有5例前置胎盘患者，其中4例在妊娠晚期有出血。1例患者在妊娠中期诊断为胎盘植入正常，但分娩时显示为前置胎盘。妊娠16至18周时前置胎盘的发生率为5.3%，分娩时降至0.58%，转换率为90%。因此，绝大多数无症状前置胎盘病例在分娩前仍无症状且会发生转换。这些患者应每隔6至8周进行系列超声检查，直至分娩或明确转换。除非前置胎盘持续超过30周或出现临床表现，否则似乎无需限制活动。
