Amsterdam UMC, University of Amsterdam, Department of Obstetrics, Amsterdam Reproduction and Development Research Institute, Meibergdreef 9, Amsterdam, the Netherlands.
Amsterdam UMC, University of Amsterdam, Department of Obstetrics, Amsterdam Reproduction and Development Research Institute, Meibergdreef 9, Amsterdam, the Netherlands.
Eur J Obstet Gynecol Reprod Biol. 2019 Sep;240:197-204. doi: 10.1016/j.ejogrb.2019.06.020. Epub 2019 Jul 4.
Low-positioned placentas which are located in the lower uterine segment (LUS), either a low-lying placenta or a placenta previa, are associated with increased obstetric risks. However, most second trimester low-positioned placentas resolve during pregnancy and have a higher position in the third trimester, without posing any risks. We performed a systematic review and meta-analysis to evaluate the proportion of second trimester low-positioned placentas that have a position towards the fundus in the third trimester. Our aim was to find a cut-off value that included all women in whom the placenta will remain low in the third trimester, thus who are at increased risk of obstetric complications. Subsequently, we assessed whether an anterior or posterior placental location influenced this proportion. We searched MEDLINE and EMBASE and clinicaltrials.gov up to April 2019 for studies on the sonographic follow-up of second trimester low-positioned placentas, with a distance between the placenta and the internal os of the cervix of 20 mm or less at a gestational age of above 15 week and a follow up after 28 weeks. Studies were scored on methodological quality using the Newcastle-Ottowa Scale (NOS). A meta-analysis was conducted to summarize the proportion of second trimester low-positioned placentas with a position towards the fundus in the third trimester. We calculated the proportion at different cut-off values of the distance from the placental edge to the internal os of the cervix (0 mm, 10 mm and 20 mm). Also, anteriorly and posteriorly located placentas and women with and without a prior cesarean delivery were compared. We included 11 eligible studies which reported on 3586 women with a low-positioned placenta in the second trimester. Proportions of placentas with a position towards the fundus in the third trimester ranged between 0.63 and 1.0. Pooled proportions were 0.90 (95% CI 0.87-0.93) for IOD <10 mm and 0.80 (95% CI 0.74-0.85) for IOD < 0 mm. Due to heterogeneity between studies, the subgroup of <20 mm could not be pooled. Overall, anteriorly located placentas more often had a position towards the fundus in the third trimester, but studies did report conflicting results. Prior cesarean section had no influence except for an IOD of <0 mm, in which women without a prior cesarean delivery more often had a placenta towards the fundus. The majority of second trimester low-positioned placentas will be located towards the fundus at the time of follow-up. However, we could not determine a cut-off value for anterior and posterior placentas that included all women at high risk. The cut-off value, placental side and prior cesarean section should be assessed in a large prospective observational study.
位置较低的胎盘位于子宫下段（LUS），无论是低位胎盘还是前置胎盘，都会增加产科风险。然而，大多数妊娠中期位置较低的胎盘会在妊娠期间自行消退，并在妊娠晚期位于较高位置，不会造成任何风险。我们进行了一项系统评价和荟萃分析，以评估妊娠中期位置较低的胎盘中有多少在妊娠晚期位于子宫底。我们的目的是找到一个包含所有在妊娠晚期胎盘仍处于低位的女性的截断值，这些女性有产科并发症的风险增加。随后，我们评估了胎盘的前位或后位是否会影响这一比例。我们检索了 MEDLINE 和 EMBASE 以及 clinicaltrials.gov 数据库，以获取截至 2019 年 4 月关于妊娠中期位置较低的胎盘超声随访的研究，这些研究的胎盘和宫颈内口之间的距离在妊娠 15 周以上时为 20mm 或更小，并且在 28 周后进行了随访。使用纽卡斯尔-渥太华量表（NOS）对研究进行了方法学质量评分。我们进行了荟萃分析，以总结妊娠中期位置较低的胎盘在妊娠晚期位于子宫底的比例。我们计算了胎盘边缘与宫颈内口之间的距离为不同截断值（0mm、10mm 和 20mm）时的比例。此外，我们比较了前位和后位胎盘以及有和无剖宫产史的女性。我们纳入了 11 项符合条件的研究，这些研究报告了 3586 例妊娠中期位置较低的胎盘。妊娠晚期胎盘位于子宫底的比例在 0.63 至 1.0 之间。汇总比例为 IOD<10mm 时为 0.90（95%CI 0.87-0.93），IOD<0mm 时为 0.80（95%CI 0.74-0.85）。由于研究之间存在异质性，因此无法对<20mm 的亚组进行汇总。总体而言，前位胎盘在妊娠晚期更常位于子宫底，但研究结果报告结果不一致。除了 IOD<0mm 外，剖宫产史没有影响，在这种情况下，没有剖宫产史的女性更常将胎盘位于子宫底。大多数妊娠中期位置较低的胎盘在随访时将位于子宫底。然而，我们无法确定包括所有高危女性的前位和后位的截断值。截断值、胎盘侧和剖宫产史应在大型前瞻性观察研究中进行评估。
