Gardosi J, Vanner T, Francis A
Department of Obstetrics and Gynaecology, Queen's Medical Centre, Nottingham, UK.
Br J Obstet Gynaecol. 1997 Jul;104(7):792-7. doi: 10.1111/j.1471-0528.1997.tb12022.x.
To examine the length of gestation according to menstrual and ultrasound scan dates, and the rate of induction of labour in a unit with a routine induction policy for prolonged pregnancy.
Retrospective analysis of computer files of 24,675 pregnancies delivered in a teaching hospital between 1988 and 1995, which had a record of the last menstrual period and a dating ultrasound scan. Detailed survey of 168 casenotes of consecutive inductions of labour to establish the indications given.
Teaching hospital with policies of routine mid-trimester ultrasound scan and routine induction for prolonged pregnancy at 290 to 294 days.
Gestational age at delivery by menstrual history and ultrasound biometry in spontaneous and induced labours.
The single largest category of reasons given for induction of labour was prolonged pregnancy. 'Post-term pregnancy', from the date of expected delivery as recorded in the notes, together with 'maternal request' and 'social factors', were the reasons given for induction of labour in 71.3% of cases. Menstrual dates systematically overestimated gestational age at term when compared with scan dates. After 41 weeks, this difference exceeded the confidence limits for second trimester scan dating error, suggesting that most pregnancies which are considered 'prolonged' according to menstrual dates are in fact mis-dated. The median gestational age for induced labours was 286 days by last menstrual period but only 280 days by scan, and most (71.5%) inductions done post-term (> 294 days) according to menstrual dates were not post-term if scan dates alone are used to calculate the gestational age. The average induction rate over the seven year study period was 16.6%. It was higher when there was any gestational age error in either direction (16.8%) compared with when menstrual and scan dates were in complete agreement (13.7%, OR 1.27, CI 1.09-1.47, P < 0.001). The induction rate was highest (up to 21.8%) in the cases where menstrual dates overstated gestational age without exceeding the usual limits for adjusting dates according to scan. Such overestimation within tolerance limits of 7, 10 or 14 days occurred in 37.1%, 45.8%, or 52.6% of all pregnancies, respectively.
Most pregnancies undergoing post-term induction are not post-term when assessed by ultrasound dates. Regardless of whether prolonged pregnancy is considered to be a risk factor requiring intervention, the proportion of pregnancies considered 'post-term' can be reduced considerably by a dating policy which ignores menstrual dates and establishes the expected delivery date on the basis of ultrasound dates alone.
根据末次月经日期和超声扫描日期来检查妊娠期长度，以及在一个对过期妊娠采用常规引产策略的科室中的引产率。
对1988年至1995年在一家教学医院分娩的24675例妊娠的计算机文件进行回顾性分析，这些妊娠有末次月经记录和一次确定孕周的超声扫描记录。对连续168例引产病历进行详细调查以确定引产指征。
一家教学医院，有孕中期常规超声扫描和在290至294天对过期妊娠进行常规引产的政策。
自然分娩和引产时根据月经史和超声生物测量法得出的分娩时的孕周。
引产的最大单一原因类别是过期妊娠。从病历记录的预期分娩日期起算的“过期妊娠”，连同“产妇要求”和“社会因素”，是71.3%病例的引产原因。与扫描日期相比，月经日期系统性地高估了足月时的孕周。41周后，这种差异超过了孕中期扫描确定孕周误差的置信限，这表明大多数根据月经日期被认为“过期”的妊娠实际上孕周计算错误。引产的末次月经孕周中位数为286天，但扫描孕周仅为280天，并且如果仅用扫描日期计算孕周，那么大多数（71.5%）根据月经日期在过期后（>294天）进行的引产并非过期妊娠。在为期七年的研究期间，平均引产率为16.6%。当孕周在任何一个方向存在误差时引产率更高（16.8%），相比之下月经日期和扫描日期完全一致时引产率为13.7%（比值比1.27，可信区间1.09 - 1.47，P < 0.001）。在月经日期高估孕周但未超过根据扫描调整日期的通常限度的病例中，引产率最高（达21.8%）。在所有妊娠中，分别有37.1%、45.8%或52.6%在7天、10天或14天的容差限度内存在这种高估情况。
根据超声日期评估时，大多数接受过期引产的妊娠并非过期妊娠。无论过期妊娠是否被视为需要干预的危险因素，通过一项忽略月经日期并仅基于超声日期确定预期分娩日期的孕周确定策略，可大幅降低被认为“过期”的妊娠比例。
