The potential critical windows for extreme ambient temperature, air pollution exposure and small for gestational age (SGA) are still unclear, and no study has explored their joint effects on SGA. In a national multi-center prospective cohort, we included 179,761 pairs of mother-infant from 16 counties of 8 provinces in China during 2014-2018. Daily averaged temperature and PM_2.5 concentration were matched to the maternal residential address to estimate personal exposure. Extreme temperature exposures were categorized by a series of percentile in each meteorological and geographic division for the entire pregnancy, each trimester and gestational week (GA-week). Generalized linear mixed models (GLMMs) and distributed lag nonlinear models (DLNMs) were used to estimate the whole pregnancy-, trimester-specific, and weekly-specific associations of extreme temperature and PM_2.5 exposures with SGA. Combined effects were evaluated with the relative excess risk due to interaction (RERI) and proportion attributable to interaction (AP). We observed that by referring to temperature at the 41st - 50th percentile, heat (>90th percentile) exposure during 13th - 29th GA-weeks was associated with SGA; odds ratio (OR) and 95 % confidence intervals (CI) was 1.16 (1.06, 1.28). For cold (<=10th percentile), inverse associations were observed during the 1st - 8th GA-weeks. PM_2.5 exposure during the 2nd - 5th and 19th - 27th GA-weeks was associated with SGA, with the strongest association in the 2nd GA-week (OR = 1.0017, 95 %CI: 1.0001, 1.0034, for a 10 μg/m³ increase). No interactive effects between ambient temperature and PM_2.5 on SGA were observed. Our findings suggest the weekly susceptibility windows for heat and PM_2.5 exposure were primarily the gestational weeks within the 2nd trimester, therefore, corresponding protective measures should be conveyed to pregnant women during routine prenatal visits to reduce exposures.

Pregnant individuals are particularly susceptible to non-optimal temperatures due to their physiological status. Moreover, pregnancy is a crucial period for programming fetal health. Quantifying the impact of non-optimal temperature exposure and the contribution of anthropogenic climate change is crucial for mitigating and adapting to climate-related health risks. However, this has not been thoroughly studied in pregnant individuals in low-income and middle-income countries (LMICs). Using data from 511 449 births across 31 LMICs from 1990 to 2018, we linked climate simulations (with and without anthropogenic forcing) to spatiotemporally resolved temperature data and birthweight records. We assessed the association between heat and cold exposure (ie, >90th and <10th percentile of temperature by region) during pregnancy and birthweight across different regions. We then used temperature simulations from both historically forced and natural-only forced climate models to estimate changes in exposure due to anthropogenic climate change and to quantify the burden of temperature-related low birthweight (ie, a birthweight <2500 g) attributable to anthropogenic climate change. Heat exposure during pregnancy, compared with the optimal temperature range, was associated with an increased risk of low birthweight in several regions: southern Asia (odds ratio 1·41, 95% CI 1·34-1·48), western Africa (1·12, 1·02-1·24), and eastern Africa (1·40, 1·27-1·55). Cold exposure increased the risk of low birthweight in central Africa (1·31, 1·10-1·56), southern Africa (1·18, 1·02-1·36), and eastern Africa (1·14, 1·02-1·26). Anthropogenic climate change contributed to approximately 59·2% (95% CI 16·6-94·3), 89·0% (51·0-100·0), and 77·3% (27·0-100·0) of heat-related low birthweight cases in southern Asia, western Africa, and eastern Africa, respectively. Conversely, in regions where cold exposure was predominant, anthropogenic climate change reduced the burden of low birthweight. Our study provides quantitative estimates of the contribution of anthropogenic climate change to the low birthweight burden in LMICs. These findings can inform strategies for climate mitigation and adaptation in LMICs and help reduce global health inequalities. National Natural Science Foundation of China.

Preterm birth is the leading cause of child mortality under 5 years of age. Temporal trends in preterm birth rates are highly heterogeneous among countries and little information exists for China. To address this data gap, we investigated annual changes in preterm birth incidence rate and explored potential determinants of these changes in Shenzhen, China. A total of 1.4 million live births, during 2003-2012, were included from the Shenzhen birth registry. Negative-binominal regression models were used to estimate the annual percent changes in incidence. To identify the potential determinants behind temporal trends, we estimated the contribution of each changing risk factor to changes in rate by calculating the difference in population-attributable risk fraction. Annual preterm birth incidence rates increased by 0.94% (95% CI 0.30%, 1.58%) overall, 3.60% (95% CI 2.73%, 4.48%) for medically induced, and 3.13% (95% CI 1.01%, 5.31%) for preterm premature rupture of membranes, but decreased by 2.34% (95% CI 1.62%, 3.06%) for spontaneous preterm labor. Higher maternal educational attainment (0.20 rate increase), lower proportion of inadequate prenatal care (0.15 rate reduction), more multipara (0.08 rate reduction), decreased proportion of preeclampsia or eclampsia (0.05 rate reduction), and larger proportion of young and older pregnant women (0.04 rate increase) were significant contributors to the overall change over time. Contributions of changing risk factors were different between preterm birth subtypes. Preterm birth rate in Shenzhen, China increased overall during 2003-2012, although trends varied across three preterm birth subtypes. The rising rates were associated with changes in maternal education and age.