The association between ambient temperature and preterm birth in Shenzhen, China: a distributed lag non-linear time series analysis

Abstract

BackgroundA few studies have examined the association between ambient temperature and preterm birth (PTB), and the results have been inconsistent. This study explored the association between ambient temperature and PTB in Shenzhen, China.MethodsData of daily singleton PTB, air pollution and meteorological variables from 2005 to 2011 were collected in Shenzhen. A distributed lag non-linear model (DLNM) was used to investigate the association of the low and high temperatures (1st, 5th, 95th, and 99th percentiles) with PTB.ResultsThe median temperature was 24.5 °C and the 1st, 5th, 95th, and 99th percentiles of daily mean temperatures were 9, 12.5, 29.9 and 30.7 °C, respectively. The prevalence of singleton PTB was 5.61 % in Shenzhen. The association between temperature and PTB was not linear. There was an immediate positive association of low temperature (1st and 5th percentiles) and a negative association of high temperature (95th and 99th percentiles) with PTB. The effect of low temperature 9 °C (1st) on PTB on the current day was stronger than that of 12.5 °C (5th), with a relative risk (RR) of 1.54 (95 % CI: 1.36–1.75) and 1.49 (95 % CI: 1.35–1.63), respectively. The cumulative RR (up to 30 days) of 9 and 12.5 °C was 1.72 (95 % CI: 1.28–2.33) and 1.96 (95 % CI: 1.60–2.39), respectively. The cumulative effects (up to 30 days) of high temperature (95th and 99th percentiles) on PTB were 0.69 (95 % CI: 0.60–0.80) and 0.62 (95 % CI: 0.52–0.74), respectively. The cumulative effect (up to 30 days) of low temperatures on vaginal delivery PTB was lower than that of the cesarean section PTB with an RR of 1.58 (95 % CI: 1.12–2.22) and 1.93 (95 % CI: 1.21–3.08), respectively.ConclusionsThis study suggests that low temperature might be a risk factor, while high temperature might be a protective factor of PTB in Shenzhen.Electronic supplementary materialThe online version of this article (doi:10.1186/s12940-016-0166-4) contains supplementary material, which is available to authorized users.

Heat Exposure and Maternal Health in the Face of Climate Change

“…Table 1 shows study characteristics and whether heat exposure had a significant effect on the adverse outcomes examined within individual studies. Of the outcomes under investigation, preterm birth was the most common, investigated in 17 studies [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. Preterm birth was defined as births occurring at less than 37 weeks of gestational age with a lower margin of 20 weeks, 22 weeks, or undefined in the studies.…”

“…Heat was significantly correlated with increased risk or rate of preterm birth in 15 of 17 studies [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 34 ]; two studies found no significant effect [ 18 , 33 ]. A protective effect was demonstrated in Shenzhen, China for extreme heat exposure and preterm birth [ 30 ]. This result was in opposition to the other 13 studies and specifically to a study conducted in nearby Guangzhou [ 29 ].…”

Independent and Combined Effects of Heatwaves and PM2.5 on Preterm Birth in Guangzhou, China: A Survival Analysis

“…We considered that this may be due, at least in part, to behavioral changes. Under extremely high temperatures, mothers are more likely to attempt to mitigate exposure, including altering clothing, drinking fluids, or using air conditioning (Carolan-Olah and Frankowska 2014; Liang et al 2016). Such adjustments may offset some of the harmful effects of very intense heatwaves.…”

“…Existing studies have usually used a series of temperature thresholds (absolute or percentiles) and durations to define heatwaves (Xu et al 2016). In our study location, some previous studies (He et al 2016;Liang et al 2016) evaluated high-temperature exposure and PTB, but the duration of hot days was not considered in their studies. Therefore, no clear evidence on appropriate absolute temperatures was available for us to define heatwaves.…”

Seasonal Variations of the Urban Thermal Environment Effect in a Tropical Coastal City

“…The annual average temperature is 23.0 ∘ C, the average low temperature is 15.4 ∘ C in January, and the average maximum temperature is 28.9 ∘ C in July [38]. The mean annual total precipitation is 1933.3 mm, with the rainy season extending from April to September.…”