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产前孕龄评估及分娩日期估算

Authors
Andrew P MacKenzie, MD
Courtney D Stephenson, DO
Edmund F Funai, MD
Section Editor
Deborah Levine, MD
Deputy Editor
Vanessa A Barss, MD, FACOG
Translators
桂婷, 住院医师

引言

超声诊断通过相对详细地评估子宫内胎儿情况从而推动了产科临床实践的进步，评估包括在妊娠的前半段进行超声检查以对孕龄(gestational age, GA)进行准确估计[1]。这一信息至关重要，因为大多数产科治疗决策都受到胎儿发育情况的强烈影响，而胎儿发育情况与胎龄密切相关。妊娠早期超声检查可降低过期妊娠引产率[2]，并且在宫外存活力界限[limit of viability，即当母亲孕龄能确保早产胎儿/婴儿有一个合理的可能性(50%可能性)在宫外长期存活]时若发生并发症，其也可改善对胎儿宫外存活能力的估计。 (参见“Periviable birth (Limit of viability)”)

本文将总结用于计算孕龄和计算估计的分娩日期[(estimated date of delivery, EDD)，或称“预产期(due date)”]的胎儿生物计量学测量指标。关于妊娠时间计算的讨论都是根据自末次月经(last menstrual period, LMP)开始的时间(即月经龄)算起，而不是从受孕开始的时间(受孕龄或胚胎龄)算起。

估算的分娩日期

从LMP来潮开始算起，则EDD为280日，若从受孕日期算起则为266日。尽管任何实验室或影像学方法均无法检测到卵母细胞在体内的受精，但体内受精发生在排卵的24小时内，而通过检测到黄体生成素(luteinizing hormone, LH)激增或通过超声检查发现围排卵期卵泡可准确地预测排卵(参见“月经周期和排卵时间的评估”)。只有4%的女性在EDD时分娩，部分原因为用于估算孕龄的方法存在不足之处，但也有部分原因在于胎儿成熟速度和自然分娩时机中存在自然生物学变异[3]。

临床评估

孕龄评估的2种临床方法为病史采集和体格检查，其中病史采集是利用LMP的日期来计算EDD。对孕龄或妊娠持续时间的临床评估反映了“月经龄”。与之相反，胚胎学家总是从受精的时间开始计算生长发育事件的时间，即“胚胎龄”。

Naegele法则 — Naegele法则是计算妊娠时间最常见的方法。EDD的计算方法是将末次月经的月份减3，日数加7。例如，若LMP日期为2月20日，则预产期为11月27日。若LMP日期是5月28日，EDD则是3月4日。这种方法假定患者的月经周期为28日，而受精发生在月经周期的第14日。

                     

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Literature review current through: 2017-06 . | This topic last updated: 2017-06-26.
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