Preterm birth (PTB), any live birth occurring before 37 weeks, is one of the major causes of morbidity and mortality among children aged younger than 5 years (Blencowe et al., 2013). Although there is a lack of actual data in many countries, it is estimated that about 15 million PTB occur annually imposing substantial direct and indirect costs on families and healthcare systems (Blencowe et al., 2013; Chawanpaiboon et al., 2019). Despite many efforts to reduce PTB incidence, almost in all countries, the rate of PTB is increasing (Blencowe et al., 2013; Chawanpaiboon et al., 2019). Infants with PTB are more likely to experience other adverse health effects during childhood and even adulthood (Blencowe et al., 2013; Frey and Klebanoff 2016; Vogel et al., 2018). As many cases of PTB have an unknown etiology, it is supposed that PTB is a multifactorial phenomenon (Frey and Klebanoff 2016). Previous epidemiological studies indicated that several factors such as young or old maternal age, maternal smoking and drinking, low socioeconomic status, and infectious disease may be involved in the etiology of PTB (Frey and Klebanoff 2016; Vogel et al., 2018). More recently, research has begun to focus on the influence of environmental and occupational exposures on the incidence of PTB. Recent meta-analysis studies indicated exposure to noise and air pollutants (Dzhambov and Lercher 2019; Khanam et al., 2021; Kumar et al., 2017; Nyadanu et al., 2022a; Runge et al., 2013; Wu et al., 2022), and working conditions such as long working hours during pregnancy (Saurel-Cubizolles et al., 2004) can increase the risk of PTB.

One of the main environmental and occupational agents have gained great attention from researchers during the last decade about its effect on pregnant women is climate change (Dehdashti et al., 2020; Poursafa et al., 2015). A review study reported the peaks of decreased gestational length births both in the winter and summer months (Beltran et al., 2013). As well, another review study found peaks of PTB both in the winter and summer seasons (Strand et al., 2011). According to these studies, likely, there is a V-shape association between the seasonal changes and the incidence of PTB with the peaks in the extreme heat and cold temperatures. However, it is observed that the effects of the high temperature can be significantly stronger than the low temperature (Zhang et al., 2017). Apart from this, other studies have investigated the temperature variations in the different time windows during the pregnancy period. A review study found that long-term high versus low-temperature exposures can be significantly associated with a greater incidence of PTB during the whole pregnancy time, trimesters, and the last month before birth (Chersich et al., 2020). In the mentioned study a significant linear association was also observed between the temperature changes and PTB incidence.

So far, following the systematic review by Chersich and their colleagues (Chersich et al., 2020), more recent studies investigated this association up to a week before birth, including each single lag day (lag0 to lag6) and cumulative lag days (Blavier et al., 2021; Cheng et al., 2021; Cushing et al., 2022; de Bont et al., 2022; Gong et al., 2021; Hough et al., 2023; Jegasothy et al., 2022; Li et al., 2021; McElroy et al., 2022; Nyadanu et al., 2022b; Ranjbaran et al., 2022; Ren et al., 2022; Son et al., 2022; Wang et al., 2023; Wu et al., 2023). However, due to controversial findings across these studies especially by taking into account variables, involving the study design, temperature index, season, and time window, this association has not been well-defined. This systematic review and meta-analysis study was performed to provide a comprehensive review and quantify the possible short-term effects of temperature variations on the incidence of PTB in the week preceding birth among pregnant women.