流产史不再是早产的危险因素

母胎医学会(SMFM)年会上报告的一项研究显示，有流产史的女性再次妊娠时早产风险不再增加。因此，现在或许应该对相关咨询指南进行相应修订。

英国剑桥大学公共卫生和初级保健系博士研究生Clare Oliver-Williams报告称，在这项纳入1992~2008年416,301例苏格兰单胎初产女性的队列研究中，曾经行人工流产的女性校正后的自发性早产几率显著增加12%。但时间段分层分析显示，随着时间的推移，该相关性逐渐变弱，并且从2000年开始不再存在。


Clare Oliver-Williams
 
上述趋势与采用对宫颈损伤越来越小的流产方式的转变相一致：未行宫颈预处理的手术流产例数急剧减少，甚至不再采用，而药物流产例数快速上升。

研究者认为，流产史与再次妊娠早产风险不再相关的原因是流产实践的改变，因为未行宫颈预处理的手术流产始终是导致这一相关性存在的根源。如果有流产史的女性准备妊娠，上述结果可使她们感到欣慰。同时，对流产前咨询也具有参考价值。

现行英国指南建议，在行流产手术之前应告知患者有关早产风险问题。鉴于目前大多数流产采用药物方法或宫颈预处理的手术方法，因此向女性提供相关咨询或许不再合适。

在英国，宫颈预处理方法通常是应用前列腺素，虽然各国所采取的方法可能有所不同，但有理由相信其他国家也不再采用宫颈损伤较大的手术方法。从理论上讲，机械扩张术可损伤宫颈，导致后续妊娠出现自发性早产。因此，研究者谨慎地认为，虽然其他国家采取未行宫颈预处理的手术流产越来越少，但上述相关性仍会存在。

选择未经产女性作为受试者的部分原因是她们其他合并因素较少，例如流产与生产的时序。但研究者认为，经产女性对研究结果不会产生任何影响，经产女性的情况或许也是如此。

这项研究的主要结果包括：校正其他因素后，有人工流产史的女性自发性早产的几率显著增加[比值比(OR)，1.12]；既往流产次数与风险之间存在量效关系：既往流产次数为1、2和3次的女性，其自发性早产几率分别增高7%、24%和37%(P<0.001)；时间段分层分析显示，1996~1999年比1992~1995年期间产妇早产几率有所增加，但此后不再增加；在整个研究期间，未行宫颈预处理的手术流产比例急剧下降(从31%降至<1%)，而药物流产比例急剧上升(由18%增至68%)。

此外，既往流产与产前死产、产时死产、新生儿死亡、小于胎龄儿、其他任何原因导致的早产或子痫前期导致的早产等其他不良结局风险显著增加不存在关联。

研究者报告无相关利益冲突。

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By: SUSAN LONDON, Internal Medicine News Digital Network

Women who have had an abortion are no longer at increased risk for preterm birth in subsequent pregnancies, and it may be time to adjust counseling guidelines accordingly, a study has shown.

In a cohort study among 416,301 nulliparous Scottish women with a first singleton birth between 1992 and 2008, those who had had a previous induced abortion had a significant 12% increase in the adjusted odds of spontaneous preterm birth, lead investigator Clare Oliver-Williams reported in a poster session at the Pregnancy Meeting, the annual meeting of the Society for Maternal-Fetal Medicine.

However, more-detailed analyses stratified by time period showed that the association weakened over time and disappeared as of about 2000.

This trend coincided with a shift toward the use of abortion practices less likely to injure the cervix: a sharp decrease to almost 0 in surgical abortions performed without cervical pretreatment and a sharp increase in medical abortions.

"We think the reason why there has been a loss of association [between previous abortion and preterm birth] is because of this change in practice: There are no longer surgical abortions without cervical pretreatment, and that was driving the association all along," Ms. Oliver-Williams said in an interview.

"If women have chosen to have an abortion previously and then go on to have an intended pregnancy, this should be reassuring to them," she said. And the findings have related implications for preabortion counseling.

Current U.K. guidelines recommend that women be advised before the procedure about a subsequent increase in the risk of preterm birth, she noted. "That might not be the most appropriate thing to tell women anymore given that the majority of abortions [now] occur through medical means or surgical means with cervical pretreatment."

Cervical pretreatment in the United Kingdom usually involves the use of a prostaglandin, and practices may differ across countries, said Ms. Oliver-Williams, a PhD candidate in the department of public health and primary care at the University of Cambridge (England). But it is reasonable to assume that other countries are also getting away from more-injurious procedures.

"The theory holds up that mechanical dilation would damage the cervix and lead to spontaneous preterm birth" in a later pregnancy, she said. "So, in a cautious way, I would suggest that the association would still exist in other countries if there was a decrease in these surgical abortions without cervical pretreatment."

Nulliparous women were chosen for analysis in part because there are fewer complicating factors for this group, such as the timing of abortions relative to births, according to Ms. Oliver-Williams. But the findings would likely be similar for multiparous women, too. "I can’t imagine why multiparity would have any impact," she said.

The main results showed that women with a previous induced abortion had significantly higher odds of spontaneous preterm birth after other factors were considered (odds ratio, 1.12), reported Ms. Oliver-Williams.

There was a dose-response relationship between the number of previous abortions and risk: Women who had had one, two, and three previous abortions had 7%, 24%, and 37% higher odds, respectively, of spontaneous preterm birth (P less than .001 for trend).

In time period–stratified analysis, the odds were elevated for women giving birth during 1992-1995 and during 1996-1999. But they were no longer so thereafter.

During the same overall study period, the proportion of all abortions that were surgical and performed without cervical pretreatment fell sharply (from 31% to less than 1%), and the proportion that were performed with medication rose sharply (from 18% to 68%).

In additional study findings, previous abortion was not associated with a significant increase in the risk of various other adverse outcomes: antepartum stillbirth, intrapartum stillbirth, neonatal death, small-for-gestational-age birth, induced preterm birth due to any reason, or induced preterm birth specifically due to preeclampsia.

Ms. Oliver-Williams disclosed no relevant financial conflicts.