译自《华尔街日报》2009年1月7日稿

在一项大规模的新研究发现，过早的择期剖腹产，甚至婴儿在理论上达到了成熟期时，可带来新生儿的健康问题。

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这个发现可能会降低这种十分流行的方法，目前每14个婴儿的出生就有一个是剖腹产，这是一种母亲选择日期的剖腹产即用外科手术助产婴儿。这项研究发表在《新英格兰医学杂志》（NEJM）上，研究发现有三分之一的择期剖腹产做得太早，即早于39周。尽管胎儿在37周后即可认为达到了怀孕期满，但大多数的医学专家长期以来一直推荐39周为界限来做择期剖腹产手术。.

对剖腹产的争论已有数年之久，健康官员不断地寻求降低剖腹产以减少产后并发症和花费。但据CDC的最新资料，在2006年美国有31%的婴儿的出生是通过剖腹产，但是剖腹产的比率在1970年才5%，而1996年才20%。世界卫生组织推荐国家的剖腹产率不应该超过15%。

许多剖腹产并没有医疗的必要性，只是为了保险以避免胎儿窘迫，比如先兆子痫---孕妇血压骤然升高。但是许多研究包括《美国妇产科杂志》十月的文章都对过早的择期剖腹产持审慎保留的态度。有些剖腹产更早到怀孕的34-36周时。

最新的研究是根据对1999-2002年美国全国13，258名择期剖腹产的分析，其中有36%的手术是在37或38周时进行的。

婴儿早期出生有较高机率的并发症。在39周出生的婴儿，有3.4%出现有某种呼吸问题，其中包括一种叫做呼吸窘迫综合症的疾病。 呼吸问题在38周的婴儿中升高到5.5%，37周中升高到8.2%。婴儿的呼吸问题一般并不引起死亡，但这些婴儿多需要住进加护病房进行护理。

另一个问题是早期剖腹产的高感染机率，这些感染需要5天以上的心脏复苏和入院治疗。

Alabama大学的产科医生Alan Tita领导了NEJM的分析，她说，“病人（孕妇）通常喜欢一到37周时就要求生产。”但是“根据目前的资料，我们推荐择期剖腹产的孕妇至少要等到39周方好。”

这项研究不包括因为急诊生产和剖腹产的妇女。该研究仅研究二次以上的孕妇，因为首次剖腹产通常都不是择期性的。

研究发现，有一半的再次剖腹产是择期性的，即美国每年大约有30万择期剖腹产的新生儿。美国每年有四百三十万新生儿，包括首次的剖腹产，大约有一百三十万剖腹产。该研究将择期剖腹产定义定为“在没有阵痛和其它确定的医学和产科分娩指征的手术分娩。”

之前的研究提示在第一次剖腹产分娩之后，下一次的阴道分娩要比另一次剖腹产对胎儿有略多的危险，但确切的资料并不存在。

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研究者认为孕妇选择早期剖腹产的主要原因是要保证她们自己的医生为自己做手术，以避免在阵痛开始不确定的时间由随机分配来的医生为她们分娩。

较富裕的妇女更可能择期早期分娩。研究表明，选择早期剖腹产的孕妇多是中产以上的人，包括白人，已婚妇女和有私家保险的妇女，以及做过围产期保健包括做过超声波检查的妇女。

Massachusetts总医院的产科主任Michael Greene在NEJM中写有附加编辑部文章认为，在多数情况下，要鼓励孕妇在39周后再做择期剖腹产手术，他说，“产科医生和病人都心照不宣，都知道这是病人的要求‘她的医生’来做接生，医生也想与病人保持良好关系，有可能的话也会想要做这种手术。”

这项研究也有其局限性，许多医学专家相信，在怀孕37周后，胎儿在母腹中呆的越久，死亡的几率越高而导致死产。目前还没有这种罕见危险的确切资料，NEJM的这项研究并不评定胎儿死亡危险。

如果医生使用羊水检查确定胎儿的肺脏已经发育成熟，那么在39周前出生也没什么问题。NEJM的研究也没收集这种检查频率方面的资料。

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Greene医生认为，该研究“需要起到这样的效果，即医生要与病人进行坦诚对话，以讨论37，38，39周分娩对新生儿和母腹中胎儿的利弊。”

Early C-Section Carries Risks, Study Finds

Elective Procedures Increase Complications for Infants When Done Before 39 Weeks

By KEITH J. WINSTEIN

Elective Caesarean-section deliveries can increase problems for a newborn if done too early -- even when the baby has technically reached full term, according to a large new study.

The findings could help diminish a widely popular practice -- now about one in every 14 births -- in which mothers choose to schedule c-sections, or surgical removal of the baby. The study, published in the New England Journal of Medicine, found that about a third of elective c-sections are done too early -- before 39 weeks. Although a fetus is considered to have reached full term after 37 weeks, most medical experts have long recommended the 39-week threshold for performing an elective c-section.

Caesarean sections have for years been controversial, and health officials have repeatedly sought to reduce their frequency to minimize post-partum complications and reduce costs. Still, the procedures accounted for 31% of U.S. births in 2006, the latest data available from the Centers for Disease Control and Prevention. That's up from just 5% in 1970 and 20% in 1996. The World Health Organization recommends that a country's rate of c-sections shouldn't exceed 15%.

To be sure, many c-sections are performed out of medical necessity, to avoid fetal distress, for instance, or pre-eclampsia, a sudden spike in the mother's blood pressure. But various studies, including one in the American Journal of Obstetrics and Gynecology in October, have cautioned against elective c-sections being performed too early. Some are done after as few as 34 to 36 weeks.

The latest study was based on an analysis of 13,258 elective Caesarean deliveries nationwide between 1999 and 2002, of which 36% were performed at 37 or 38 weeks. The rest of the procedures that figured in the NEJM study were performed at a later gestational age.

The earlier deliveries had a higher rate of complications. Among babies born at 39 weeks, 3.4% had certain breathing problems, including one called respiratory distress syndrome. The frequency of such problems rose to 5.5% for babies delivered at 38 weeks, and to 8.2% at 37 weeks. An infant's breathing problems don't usually cause lasting effects, but such babies are more likely to have to be admitted for intensive care.

Other problems that occurred with higher frequency among the early c-sections were infections, the need for cardiac resuscitation and hospitalizations of greater than five days.

"The patient [mother] usually would like to be delivered as soon as they hit term -- 37 weeks," says Alan Tita, an obstetrician at the University of Alabama who led the NEJM analysis. "And the physician would like to accommodate them." But "given the available information, we would recommend that women who plan to have an elective Caesarean wait until the 39th week, at least."

The study didn't include women who went into labor or who had c-sections because of medical emergencies. The study looked only at repeat pregnancies, since a woman's first c-section usually isn't elective.

About half of all repeat Caesarean deliveries are considered to be elective, the study found, meaning there are roughly 300,000 such births in the U.S. every year. That's out of about 4.3 million total births, and roughly 1.3 million Caesareans, including first-time c-sections. The study defined elective as "a delivery performed in the absence of labor or other recognized medical or obstetrical indications for delivery."

Previous studies have suggested that after one Caesarean delivery, future vaginal births are slightly more risky for babies than having another c-section. But definitive data don't exist.

Researchers say the main reason a woman schedules an early c-section is to make sure her own doctor is available, avoiding the possibility of a randomly assigned physician at the unpredictable time when labor begins.

Wealthier women appear more likely to schedule early deliveries. The study showed that women opting for early c-sections at an above-average rate include whites, married women and those with private insurance, and women who had had prenatal care that included ultrasounds.

"Every obstetrician and patient knows that this is driven by the patient wanting 'her doctor' to do the delivery, and the doctor wants to maintain that patient relationship and wants to do it if possible," says Michael Greene, the director of obstetrics at the Massachusetts General Hospital, who wrote an accompanying editorial in NEJM encouraging elective c-sections not be done before 39 weeks in most cases.

The study had some limitations. Many medical experts believe that the longer a baby stays in the womb after 37 weeks, the higher the chance it will die, leading to a stillbirth. There is no definitive data on that rare risk, however, and the NEJM study didn't assess risk of fetal death.

Also, birth before 39 weeks may be appropriate if doctors verify that a baby's lungs have finished developing, using an amniotic-fluid test. The NEJM study didn't collect data on how often that test was done.

The study "needs to result in a frank conversation between doctor and patient about what the risks and tradeoffs are about delivering at 37, 38, 39 [weeks], in terms of both risk to the newborn and risk to the fetus in utero," says Dr. Greene.