择期再次剖宫产时机选择较复杂

明尼阿波利斯——加拿大不列颠哥伦比亚大学妇产科流行病专家Jennifer Hutcheon博士在儿科与围产期流行病研究学会(SPPER)年会上报告的一项最新研究结果表明，足月后期行择期再次剖宫产(ERC)可意外增加急诊剖宫产孕妇比例，且急诊分娩还与校正混杂因素后的不良母婴结局风险增加2倍相关。


Jennifer Hutcheon博士
 
既往研究显示，与足月后期(39~41周)相比，足月早期(37~38周)行ERC的新生儿呼吸系统并发症发生率较高。美国妇产科医师协会(ACOG)也不赞成在39周前行ERC，除非有胎儿肺部发育成熟的证据。然而，最近分别有美国和荷兰的研究报告显示，35%~55%的ERC发生在39周前。为确保能够采取相应预防措施，有必要更好了解足月早期行ERC的潜在风险和相关机制。

为此，研究者利用2008~2011年不列颠哥伦比亚省围产期登记数据库中9,206例低风险ERC产妇的生育记录，分析了13家主要妇产中心足月早期分娩率与急诊剖宫产分娩率的相关性。足月早期定义为孕期37周0天~38周6天。不良产妇结局定义为出现产妇死亡、心脏骤停、产科休克、需要输血的产后出血或子宫切除、通过气管内导管的机械通气或严重内科疾病。不良新生儿结局定义为出现任何院内新生儿死亡、新生儿癫痫或需要正压通气的呼吸系统疾病。分析排除了疑似宫内生长受限、多胎、先天异常、糖尿病、高血压、心脏或肾脏疾病孕妇。

结果显示，55%的ERC分娩发生在39周之前，且不同妇产中心的差异较大，范围为35%~72%。总体上，15%的ERC分娩为急诊剖宫产，各中心差异也较大。医院足月早期分娩率与急诊剖宫产率呈高度负相关(r=–0.86，P<0.001)。例如，39周前ERC分娩率为72%的医院，需要急诊剖宫产的产妇比例<10%，而39周前ERC分娩率为35%的医院，1/3的产妇需要急诊剖宫产。

单变量分析显示，急诊剖宫产与不良产妇结局风险[比值比(OR)=2.1]和不良新生儿结局风险(OR=2.3)显著增加相关，与产科伤口感染(OR=1.4)和全身麻醉药使用(OR=1.7)非显著性增加相关。校正产妇年龄、体重指数、既往剖腹产次数以及医院产科规模后的多变量分析显示，不良产妇结局、不良新生儿结局、产科伤口感染和全身麻醉药使用的OR值分别为2.1、 2.5、1.2和1.8。除产科伤口感染外，其他均呈显著差异。

研究者承认，确认计划分娩方式较困难，部分符合“再次”指征或“产妇要求/剖宫产后阴道分娩(VBAC)被拒绝”的剖宫产产妇或许曾计划采用阴道分娩方式。为此，研究者考察了住院与实际分娩的时间间隔，发现中位间隔时间<3 h，所有不良结局产妇间隔时间均<4 h，提示产妇多为计划性剖宫产而非VBAC被拒绝者。

有与会者询问能否根据上述结果确定既能减少急诊剖宫产风险、又能尽量减少不良新生儿结局风险的“最佳孕期”，研究者答复称根据上述数据尚不能确定，选择最佳孕期需要权衡上述两种相互矛盾的风险。此外，风险还因孕妇自身情况和入住医院类型不同而有所差异。

鉴于结果显示39周前ERC率与急诊剖宫产率呈负相关，与会者询问这是否意味着应在39周前更多地实施剖宫术。研究者称，现在还不建议更多选择足月早期剖宫产，应更多考虑改变分娩时机的潜在副作用。目前需要做好充分准备工作，评估现行政策是否存在负面影响。

该研究由不列颠哥伦比亚省围产期服务局(PSBC)资助，研究者报告无相关利益冲突。

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By: PATRICE WENDLING, Ob.Gyn. News Digital Network
MINNEAPOLIS – Shifting the timing of elective repeat cesareans to late term may have the unintended consequence of increasing the proportion of women needing an emergency cesarean section, results of a new study suggest.

Moreover, these emergency deliveries were associated with a twofold increased risk of adverse maternal and neonatal outcomes after adjustment for confounders, Jennifer Hutcheon, Ph.D., said at the annual meeting of the Society for Pediatric and Perinatal Epidemiologic Research.
 
Previous studies have established that elective repeat cesarean sections performed at early-term gestation, 37-38 weeks, have higher rates of neonatal respiratory complications than late-term deliveries at 39-41 weeks.

The American College of Obstetricians and Gynecologists (ACOG) discourages elective cesarean delivery before 39 weeks of gestation unless there is evidence of fetal lung maturity.

A recent report from the United States and a report from the Netherlands, however, indicate that 35%-55% of elective repeat cesarean deliveries are performed before 39 weeks, said Dr. Hutcheon, an epidemiologist in obstetrics and gynecology at the University of British Columbia, Vancouver.

"A better understanding of potential risks and their mechanisms is needed in order to make sure we implement preventive measures," she said.

To explore this, the researchers used the birth records of 9,206 low-risk women undergoing a planned repeat cesarean delivery in the British Columbia Perinatal Database Registry for 2008-2011, and calculated the correlation between institutional rates of early-term delivery and rates of emergency cesarean delivery for each of the 13 major obstetrical centers in British Columbia. Early term was defined as 37 weeks, 0 days, to 38 weeks, 6 days.

Adverse maternal outcome was defined as any occurrence of maternal mortality, cardiac arrest, obstetric shock, postpartum hemorrhage requiring transfusion or hysterectomy, mechanical ventilation through endotracheal tube, or severe medical morbidity. Adverse neonatal outcome was defined as any in-hospital newborn death, neonatal seizures, or respiratory morbidity requiring positive-pressure ventilation.

The analysis excluded women with suspected intrauterine growth restriction, multiples, congenital anomalies, diabetes, hypertension, or cardiac or renal disease.

In British Columbia, 55% of the elective repeat C-section deliveries were done before 39 weeks, Dr. Hutcheon said. There was considerable variation between institutions, with some centers performing only 35% of cases before 39 weeks and others 72%.

Overall, 15% of repeat cesarean deliveries in the province were performed under emergency timing. Once again, rates ranged between 35% and 72% at the different institutions.

There was a strong negative correlation between institutional rates of early-term delivery and emergency cesareans (r = –0.86; P less than .001), she said. For example, the institution with 72% of its elective repeat cesareans delivered before 39 weeks had fewer than 10% of women needing an emergency cesarean. On the other hand, the institution doing only 35% of elective cesareans before 39 weeks had one in three women going into labor and requiring emergency cesarean delivery.

In a univariate analysis, emergency cesarean delivery was associated with a significantly increased risk of adverse maternal outcome (odds ratio 2.1) and adverse neonatal outcome (OR 2.3), and a modest, nonsignificant increase in obstetrical wound infection (OR 1.4) and use of general anesthesia (OR 1.7), Dr. Hutcheon said.

In a multivariate analysis that adjusted for maternal age, body mass index, number of previous cesareans, and institutional obstetrical volume, the odds ratios were 2.1, 2.5, 1.2, and 1.8, for adverse maternal outcome, adverse neonatal outcome, obstetrical wound infection, and use of general anesthesia, respectively. All differences were significant except for obstetrical wound infection.

Dr. Hutcheon acknowledged that identifying the planned mode of delivery was challenging, and that some of the cesareans performed for an indication of "repeat" or "maternal request/VBAC [vaginal birth after cesarean] declined" may actually have been attempted vaginal deliveries.

To get a handle on this, the investigators looked at the time between hospital admission and when the delivery was actually performed. What they found was that the median interval was less than 3 hours, and was less than 4 hours for all of the cases with adverse outcomes.

"This is certainly more suggestive of a planned cesarean delivery rather than a failed VBAC attempt, where we would expect that interval to be quite a bit longer, although we can’t be sure," she said.

During a discussion of the results, an attendee asked whether it’s possible from the data to identify a "gestational sweet spot" that would reduce the risk of an emergency cesarean and yet be late enough to minimize the risk of adverse neonatal outcomes. Dr. Hutcheon said that is not possible from their data, and that this requires weighing two competing risks.

"You’re weighing a baby in the NICU [neonatal intensive care unit] and the potential for maternal complications, and those risks may be weighed differently by different people," she said, adding that this risk also varies depending on whether the delivery is at an academic center or a community hospital.

Finally, another attendee said the finding that institutions with high rates of repeat cesareans before 39 weeks are doing fewer emergency cesarean deliveries implies that obstetricians should be performing more cesareans before 39 weeks.

Dr. Hutcheon said, "I’m not trying to make the case that we should be doing more early-term elective cesarean deliveries. I think the point is more that we need to be more aware that if we’re introducing policies to try to shift the timing of delivery, this is going to be a side effect. And we need to plan for it better ... and to evaluate our policies to see if there are any adverse effects."

Perinatal Services BC sponsored the study. Dr. Hutcheon and her coauthors reported no conflicts.