Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark.
Pharmacovigilance Research Center, Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
JAMA Netw Open. 2022 Feb 1;5(2):e2145800. doi: 10.1001/jamanetworkopen.2021.45800.
Preterm birth, particularly extremely preterm birth, has been associated with substantial morbidity and mortality. Research during SARS-CoV-2-related lockdowns revealed reductions in the more severe subtypes of preterm birth in some countries, suggesting the presence of preventable risk factors, such as infectious diseases or social behavior. Seasonality may provide a similar means of assessing natural changes in the daily life of pregnant individuals that were similar to those experienced during the COVID-19 lockdown period.
To evaluate the association between seasonality and extremely preterm birth.
DESIGN, SETTING, AND PARTICIPANTS: This nationwide cohort study included 1 136 143 pregnancies in Denmark with onset between January 1, 1997, and December 31, 2016, in which the fetuses survived 21 completed weeks of gestation. Pregnancies were followed up until preterm birth, fetal death, or 37 completed weeks of gestation. Data were analyzed from September 2020 to September 2021.
Season during gestation (primary exposure) and season of pregnancy onset.
The main outcome of extremely preterm birth was defined as a live birth occurring between 22 weeks, 0 days' gestation and 27 weeks, 6 days' gestation. Cox regression analyses were used to estimate hazard ratios (HRs) for season during gestation and season of pregnancy onset, with adjustment for socioeconomic and demographic factors.
Among 662 338 pregnant individuals, the median age at pregnancy onset was 30.0 years (IQR, 6.0 years). Of 1 136 143 pregnancies, 2009 extremely preterm births (cumulative incidence, 0.18%) were identified during follow-up. Season during gestation was associated with extremely preterm birth, with cumulative incidences of 0.17% (95% CI, 0.16%-0.19%) in spring, 0.18% (95% CI, 0.17%-0.20%) in summer, 0.20% (95% CI, 0.18%-0.21%) in autumn, and 0.16% (95% CI, 0.14%-0.17%) in winter. Compared with winter, the adjusted HRs (AHRs) for the risk of extremely preterm birth were 1.11 (95% CI, 0.97-1.26) for spring, 1.15 (95% CI, 1.02-1.31) for summer, and 1.25 (95% CI, 1.10-1.42) for autumn. The number of extremely preterm births associated with the increased risk in the spring, summer, and autumn was 56.1 (95% CI, 18.2-99.7), representing 2.8% (95% CI, 0.9%-5.0%) of all extremely preterm births in the study. Season of pregnancy onset was not associated with the risk of extremely preterm birth in spring (AHR, 0.98; 95% CI, 0.95-1.01) or summer (AHR, 1.00; 95% CI, 0.96-1.03) compared with winter, but a slight increase in risk was observed in autumn (AHR, 1.05; 95% CI, 1.02-1.09) compared with winter.
In this large, national cohort study, seasonality was associated with 2.8% of all extremely preterm births. Season during gestation was associated with the rate of extremely preterm birth, suggesting the presence of potential risk factors associated with season that may be preventable. Further research to identify risk factors for extremely preterm birth associated with seasonality is warranted.
早产，尤其是极早产，与大量发病率和死亡率有关。在与 SARS-CoV-2 相关的封锁期间进行的研究表明，在一些国家，更严重的早产亚型有所减少，这表明存在可预防的风险因素，如传染病或社会行为。季节性可能提供了一种类似的方法，可以评估与怀孕个体日常生活相关的自然变化，这些变化与 COVID-19 封锁期间的变化相似。
评估季节性与极早产之间的关系。
设计、地点和参与者：这项全国性队列研究包括丹麦 1997 年 1 月 1 日至 2016 年 12 月 31 日期间出生的 1136143 例妊娠，这些妊娠的胎儿在 21 周完整妊娠后存活。对妊娠进行随访，直至早产、胎儿死亡或 37 周完整妊娠。数据于 2020 年 9 月至 2021 年 9 月进行分析。
妊娠期间的季节（主要暴露）和妊娠开始时的季节。
极早产的主要结局定义为发生在 22 周零 0 天至 27 周零 6 天之间的活产。使用 Cox 回归分析估计妊娠期间季节和妊娠开始时季节的危险比（HR），并进行社会经济和人口因素的调整。
在 662338 例孕妇中，妊娠开始时的中位年龄为 30.0 岁（IQR，6.0 岁）。在 1136143 例妊娠中，在随访期间发现 2009 例极早产（累积发生率，0.18%）。妊娠期间的季节与极早产有关，春季的累积发生率为 0.17%（95%CI，0.16%-0.19%），夏季为 0.18%（95%CI，0.17%-0.20%），秋季为 0.20%（95%CI，0.18%-0.21%），冬季为 0.16%（95%CI，0.14%-0.17%）。与冬季相比，春季极早产的风险调整 HR（AHR）为 1.11（95%CI，0.97-1.26），夏季为 1.15（95%CI，1.02-1.31），秋季为 1.25（95%CI，1.10-1.42）。春季、夏季和秋季与风险增加相关的极早产病例数分别为 56.1（95%CI，18.2-99.7），占研究中所有极早产的 2.8%（95%CI，0.9%-5.0%）。妊娠开始时的季节与春季（AHR，0.98；95%CI，0.95-1.01）或夏季（AHR，1.00；95%CI，0.96-1.03）极早产的风险无关，但秋季的风险略有增加（AHR，1.05；95%CI，1.02-1.09）与冬季相比。
在这项大型的全国性队列研究中，季节性与所有极早产的 2.8%有关。妊娠期间的季节与极早产的发生率有关，这表明存在与季节相关的潜在可预防风险因素。有必要进一步研究与季节性相关的极早产风险因素。
