Previous studies of fetal death with maternal influenza have been inconsistent. We explored the effect of maternal influenza-like illness (ILI) in pregnancy on the risk of fetal death, distinguishing between diagnoses during regular influenza seasons and the 2009/2010 pandemic and between trimesters of ILI. We used birth records from the Medical Birth Registry of Norway to identify fetal deaths after the first trimester in singleton pregnancies (2006-2013). The Norwegian Directorate of Health provided dates of clinical influenza diagnoses by primary-health-care providers, whereas dates of laboratory-confirmed influenza A (H1N1) diagnoses were provided by the Norwegian Surveillance System for Communicable Diseases. We obtained dates and types of influenza vaccinations from the Norwegian Immunisation Registry. Cox proportional-hazards regression models were fitted to estimate hazard ratios (HRs) of fetal death, with associated 95% confidence intervals (CIs), comparing women with and without an ILI diagnosis in pregnancy. There were 2510 fetal deaths among 417,406 eligible pregnancies. ILI during regular seasons was not associated with increased risk of fetal death: adjusted HR = 0.90 (95% CI 0.64-1.27). In contrast, ILI during the pandemic was associated with substantially increased risk of fetal death, with an adjusted HR of 1.75 (95% CI 1.21-2.54). The risk was highest following first-trimester ILI (adjusted HR = 2.28 [95% CI 1.45-3.59]). ILI during the pandemic-but not during regular seasons-was associated with increased risk of fetal death in the second and third trimester. The estimated effect was strongest with ILI in first trimester.

中文翻译：

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怀孕期间的季节性和大流行性流感以及胎儿死亡的风险：一项基于挪威注册表的队列研究。

先前关于孕产妇流感引起的胎儿死亡的研究一直不一致。我们探讨了孕产妇流感样疾病（ILI）在妊娠中对胎儿死亡风险的影响，从而区分了常规流感季节和2009/2010大流行期间的诊断以及ILI的三个月之间的诊断。我们使用挪威医疗出生登记处的出生记录来确定单胎妊娠的早孕期（2006-2013年）后的胎儿死亡。挪威卫生局提供了由初级卫生保健提供者提供的临床流感诊断的日期，而实验室确认的甲型流感（H1N1）诊断的日期则由挪威传染病监测系统提供。我们从挪威免疫注册处获得了流感疫苗接种的日期和类型。拟合Cox比例风险回归模型以估计胎儿死亡的风险比（HRs），并与95％的置信区间（CIs）进行比较，比较孕妇是否有ILI诊断。417,406例合格妊娠中，有2510例胎儿死亡。正常季节的ILI与胎儿死亡风险增加无关：校正后的HR = 0.90（95％CI 0.64-1.27）。相反，大流行期间的ILI与胎儿死亡风险大幅增加相关，调整后的HR为1.75（95％CI 1.21-2.54）。孕早期ILI后的风险最高（调整后的HR = 2.28 [95％CI 1.45-3.59]）。大流行期间（而非正常季节）发生的ILI与孕中期和中期的胎儿死亡风险增加有关。ILI在孕早期估计效果最强。