Tremewan R N, Chandra M, Duff G B
N Z Med J. 1980 Aug 27;92(666):151-3.
Thirteen women who were found to have a low lying placenta on ultrasound scan during the mid-trimester were followed prospectively with repeated ultrasound examinations in older to observe changes in placental position and to determine the prognostic significance of low-lying placentae found during the mid-trimester. Two women aborted spontaneously and in the remainder the placenta ceased to be previa by 30 to 32 weeks gestation ie about the time of the formation of the lower uterine segment.
13名在孕中期超声检查发现胎盘位置低的女性接受了前瞻性随访，定期进行超声复查，以观察胎盘位置的变化，并确定孕中期发现的低置胎盘的预后意义。两名女性自然流产，其余女性的胎盘在妊娠30至32周时不再前置，即大约在下段子宫形成的时候。
