OBJECTIVES To investigate the effectiveness of routine ultrasonography in the third trimester in reducing adverse perinatal outcomes in low risk pregnancies compared with usual care and the effect of this policy on maternal outcomes and obstetric interventions. DESIGN Pragmatic, multicentre, stepped wedge cluster randomised trial. SETTING 60 midwifery practices in the Netherlands. PARTICIPANTS 13 046 women aged 16 years or older with a low risk singleton pregnancy. INTERVENTIONS 60 midwifery practices offered usual care (serial fundal height measurements with clinically indicated ultrasonography). After 3, 7, and 10 months, a third of the practices were randomised to the intervention strategy. As well as receiving usual care, women in the intervention strategy were offered two routine biometry scans at 28-30 and 34-36 weeks' gestation. The same multidisciplinary protocol for detecting and managing fetal growth restriction was used in both strategies. MAIN OUTCOME MEASURES The primary outcome measure was a composite of severe adverse perinatal outcomes: perinatal death, Apgar score <4, impaired consciousness, asphyxia, seizures, assisted ventilation, septicaemia, meningitis, bronchopulmonary dysplasia, intraventricular haemorrhage, periventricular leucomalacia, or necrotising enterocolitis. Secondary outcomes were two composite measures of severe maternal morbidity, and spontaneous labour and birth. RESULTS Between 1 February 2015 and 29 February 2016, 60 midwifery practices enrolled 13 520 women in mid-pregnancy (mean 22.8 (SD 2.4) weeks' gestation). 13 046 women (intervention n=7067, usual care n=5979) with data based on the national Dutch perinatal registry or hospital records were included in the analyses. Small for gestational age at birth was significantly more often detected in the intervention group than in the usual care group (179 of 556 (32%) v 78 of 407 (19%), P<0.001). The incidence of severe adverse perinatal outcomes was 1.7% (n=118) for the intervention strategy and 1.8% (n=106) for usual care. After adjustment for confounders, the difference between the groups was not significant (odds ratio 0.88, 95% confidence interval 0.70 to 1.20). The intervention strategy showed a higher incidence of induction of labour (1.16, 1.04 to 1.30) and a lower incidence of augmentation of labour (0.78, 0.71 to 0.85). Maternal outcomes and other obstetric interventions did not differ between the strategies. CONCLUSION In low risk pregnancies, routine ultrasonography in the third trimester along with clinically indicated ultrasonography was associated with higher antenatal detection of small for gestational age fetuses but not with a reduced incidence of severe adverse perinatal outcomes compared with usual care alone. The findings do not support routine ultrasonography in the third trimester for low risk pregnancies. TRIAL REGISTRATION Netherlands Trial Register NTR4367.

中文翻译：

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常规的早期三个月超声检查对降低低危妊娠围产期不良结局的效果（IRIS研究）：全国性，实用性，多中心性，阶梯楔形聚类随机试验。

目的研究与常规护理相比，妊娠晚期常规超声检查在降低低危妊娠围产期不良结局方面的有效性，以及该政策对孕产妇结局和产科干预措施的影响。设计实用，多中心，阶梯式楔形聚类随机试验。在荷兰开展了60次助产实践。参加者13 046名16岁或以上的妇女具有低风险的单胎妊娠。干预60种助产实践提供了常规护理（使用临床指示的超声检查来测量胎底高度）。在3、7和10个月后，三分之一的实践被随机分配到干预策略中。除了接受常规护理外，在干预策略中的妇女在妊娠28-30周和34-36周时接受了两次常规生物特征扫描。两种策略均使用相同的多学科协议来检测和管理胎儿生长受限。主要观察指标主要观察指标是围产期严重不良后果的综合指标：围产期死亡，Apgar评分<4，意识障碍，窒息，癫痫发作，辅助通气，败血病，脑膜炎，支气管肺发育不良，脑室内出血，脑室白带，肾小管炎或肾炎。次要结果是严重母亲发病率，自然分娩和分娩的两种综合指标。结果从2015年2月1日到2016年2月29日，有60例助产习俗招募了13 520名处于妊娠中期的妇女（平均妊娠22.8（SD 2.4）周）。13046名女性（干预n = 7067，通常的护理（n = 5979）以及基于国家荷兰围产期注册中心或医院记录的数据都包括在分析中。与常规护理组相比，干预组中出生时胎龄较小的比例明显更高（556个中的179个（32％）v 407个中的78个（19％），P <0.001）。干预策略的严重不良围产期结局发生率为1.7％（n = 118），常规护理为1.8％（n = 106）。调整混杂因素后，两组之间的差异不显着（赔率比为0.88，95％置信区间为0.70至1.20）。干预策略显示引产的发生率较高（1.16，1.04至1.30），而引产的发生率较低（0.78，0.71至0.85）。两种策略之间的产妇预后和其他产科干预措施没有差异。结论在低危妊娠中，妊娠中期常规超声检查和临床超声检查与胎龄胎儿较小的高产前检测有关，但与单独常规护理相比，重症围生期不良不良后果发生率降低。该发现不支持妊娠晚期低危妊娠的常规超声检查。试用注册荷兰试用注册号NTR4367。该发现不支持妊娠晚期低危妊娠的常规超声检查。试用注册荷兰试用注册NTR4367。该发现不支持妊娠晚期低危妊娠的常规超声检查。试用注册荷兰试用注册NTR4367。