BACKGROUND Increases in the proportion of the population with increased likelihood of cesarean section (CS) have been postulated as a driving force behind the rise in CS rates worldwide. The aim of the study was to assess if changes in selected maternal risk factors for CS are associated with changes in CS births from 1999 to 2016 in Norway. METHODS AND FINDINGS This national population-based registry study utilizes data from 1,055,006 births registered in the Norwegian Medical Birth Registry from 1999 to 2016. The following maternal risk factors for CS were included: nulliparous/≥35 years, multiparous/≥35 years, pregestational diabetes, gestational diabetes, hypertensive disorders, previous CS, assisted reproductive technology, and multiple births. The proportion of CS births in 1999 was used to predict the number of CS births in 2016. The observed and predicted numbers of CS births were compared to determine the number of excess CS births, before and after considering the selected risk factors, for all births, and for births stratified by 0, 1, or >1 of the selected risk factors. The proportion of CS births increased from 12.9% to 16.1% (+24.8%) during the study period. The proportion of births with 1 selected risk factor increased from 21.3% to 26.3% (+23.5%), while the proportion with >1 risk factor increased from 4.5% to 8.8% (+95.6%). Stratification by the presence of selected risk factors reduced the number of excess CS births observed in 2016 compared to 1999 by 67.9%. Study limitations include lack of access to other important maternal risk factors and only comparing the first and the last year of the study period. CONCLUSIONS In this study, we observed that after an initial increase, proportions of CS births remained stable from 2005 to 2016. Instead, both the size of the risk population and the mean number of risk factors per birth continued to increase. We observed a possible association between the increase in size of risk population and the additional CS births observed in 2016 compared to 1999. The increase in size of risk population and the stable CS rate from 2005 and onward may indicate consistent adherence to obstetric evidence-based practice in Norway.

中文翻译：

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1999 年至 2016 年挪威产妇危险因素的变化及其与剖宫产变化的关联：一项基于人口的描述性登记研究。

背景 剖宫产 (CS) 可能性增加的人口比例的增加已被假定为全球剖宫产率上升的驱动力。该研究的目的是评估 1999 年至 2016 年挪威 CS 的选定孕产妇风险因素的变化是否与 CS 出生的变化有关。方法和结果 这项全国性的基于人群的登记研究利用了 1999 年至 2016 年在挪威医学出生登记处登记的 1,055,006 名新生儿的数据。包括以下母体 CS 风险因素：未生育/≥35 岁、经产/≥35 岁、妊娠前糖尿病、妊娠糖尿病、高血压疾病、既往 CS、辅助生殖技术和多胞胎。1999年CS出生比例用于预测2016年CS出生人数。将观察到的和预测的 CS 出生数进行比较，以确定在考虑所选风险因素之前和之后，对于所有出生以及按 0、1 或 >1 所选风险因素分层的出生，CS 出生过多的数量。在研究期间，CS 出生的比例从 12.9% 增加到 16.1% (+24.8%)。具有 1 个选定风险因素的出生比例从 21.3% 增加到 26.3% (+23.5%)，而具有 >1 个风险因素的出生比例从 4.5% 增加到 8.8% (+95.6%)。与 1999 年相比，根据选定风险因素的存在分层，2016 年观察到的超额 CS 出生数量减少了 67.9%。研究局限性包括无法获得其他重要的孕产妇风险因素，并且仅比较研究期间的第一年和最后一年。结论 在本研究中，我们观察到，在最初的增长之后，2005 年至 2016 年 CS 出生的比例保持稳定。相反，风险人群的规模和每个出生的平均风险因素数量都在继续增加。与 1999 年相比，我们观察到风险人群规模的增加与 2016 年观察到的额外 CS 出生之间可能存在关联。 风险人群规模的增加和 2005 年及以后的稳定 CS 率可能表明对产科循证医学的一贯坚持在挪威练习。