Supplementary Material for: Outborns or Inborns: Where Are the Differences? A Comparison Study of Very Preterm Neonatal Intensive Care Unit Infants Cared for in Australia and New Zealand and in Canada

Background: Very preterm infants born outside tertiary centers are at higher risks of adverse outcomes than inborn infants. Regionalization of perinatal care has been introduced worldwide to improve outcomes. Objective: To compare the risk-adjusted outcomes of both inborn and outborn infants cared for in tertiary neonatal intensive care units in Australia and New Zealand and in Canada. Methods: Deidentified data of infants Results: ANZNN had lower rates of outborns compared to CNN (13 vs. 19%), particularly of late admissions (>2 days of age; 5.8 vs. 22.2% of outborns) who had high morbidity rates. After adjusting for confounding variables including gestation, ANZNN inborn infants had lower odds of chronic lung disease [CLD; 17.0 vs. 23.3%; adjusted odds ratio (AOR) = 0.70, 95% CI: 0.64-0.77], severe neurological injuries on ultrasound (SNI; 4.1 vs. 6.7%; AOR = 0.62, 95% CI: 0.53-0.73), severe retinopathy (5.6 vs. 7%; AOR = 0.71, 95% CI: 0.59-0.84) and necrotizing enterocolitis (3.5 vs. 5.4%; AOR = 0.67, 95% CI: 0.56-0.79), but no difference in mortality odds. After excluding the late outborn admissions, ANZNN outborns had lower odds of SNI (AOR = 0.43, 95% CI: 0.32-0.58) and CLD (AOR = 0.63, 95% CI: 0.49-0.81) than CNN. Conclusions: ANZNN inborn and early admitted outborn infants had lower odds of neonatal morbidities than their CNN counterparts. However, compared to ANZNN, the higher CNN rates of outborns and their late admissions are likely related to the differences in regionalization and referral practices, and may explain differences in outcomes.

背景：在非三级医疗中心分娩的极早产儿（very preterm infants），其不良结局发生风险高于院内分娩婴儿（inborn infants）。目前全球已推广围产期医疗区域化（regionalization of perinatal care）模式，以改善围产期结局。
目的：比较澳大利亚新西兰新生儿网络（Australian and New Zealand Neonatal Network, ANZNN）与加拿大新生儿网络（Canadian Neonatal Network, CNN）所辖三级新生儿重症监护病房（tertiary neonatal intensive care units）内，院内分娩婴儿与院外分娩婴儿（outborn infants）的校正后不良结局风险。
方法：婴儿去标识化数据。
结果：澳大利亚新西兰新生儿网络（ANZNN）的院外分娩婴儿占比低于加拿大新生儿网络（CNN）（13% vs. 19%），其中出生后2天以上入院的延迟入院院外分娩婴儿占院外分娩婴儿的比例差异尤为显著（ANZNN为5.8%，CNN为22.2%），此类婴儿的并发症发病率较高。在校正胎龄等混杂变量后，ANZNN院内分娩婴儿的慢性肺疾病（Chronic Lung Disease, CLD）发生风险更低：ANZNN发生率为17.0%，CNN为23.3%，校正比值比（adjusted odds ratio, AOR）为0.70（95%置信区间：0.64~0.77）；超声检查提示的严重神经系统损伤（Severe Neurological Injuries on ultrasound, SNI）发生率分别为4.1% vs. 6.7%，AOR=0.62（95%CI：0.53~0.73）；严重视网膜病变（severe retinopathy）发生率分别为5.6% vs. 7%，AOR=0.71（95%CI：0.59~0.84）；坏死性小肠结肠炎（necrotizing enterocolitis）发生率分别为3.5% vs. 5.4%，AOR=0.67（95%CI：0.56~0.79）；但两组的死亡风险无显著差异。在排除延迟入院的院外分娩婴儿后，ANZNN院外分娩婴儿的严重神经系统损伤（AOR=0.43，95%CI：0.32~0.58）与慢性肺疾病（AOR=0.63，95%CI：0.49~0.81）发生风险仍低于CNN对应群体。
结论：ANZNN的院内分娩婴儿与早期入院的院外分娩婴儿，其新生儿并发症发生风险均低于CNN对应群体。但相较于ANZNN，CNN更高的院外分娩婴儿占比以及延迟入院婴儿比例，或与两地的围产期医疗区域化及转诊模式差异相关，这或可解释两组间的结局差异。