Trends, seasonality and effect of ambient temperature on preterm delivery

Asnat Walfisch, Eli Kabakov, Michael Friger, Eyal Sheiner

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Purpose: To identify trends in preterm delivery (PTD) as well as seasonality, temporal variation and the effect of heat stress on its incidence. Materials and methods: In this retrospective population-based study, we included all deliveries taking place at the Soroka University Medical Center between the years 1988–2012. A time series database was built including meteorological factors and the number of spontaneous versus induced PTDs for each day. Data were analyzed using time–series analyses. Results: During the study period, 263 709 deliveries occurred, 7.9% of which were preterm. Spontaneous PTD rate steadily decreased, while induced PTD rate increased. A significant annual and seasonal variation was noted in PTD incidence. A significant higher incidence of spontaneous PTD was demonstrated during the summer period with an incidence rate ratio (IRR) of 4.1 (95%CI: 3.1–5.5; p < 0.001). This trend was not significant for induced PTD. A significant linear association was noted between the heat-stress index and the rates of spontaneous (IRR = 1.07, 95%CI: 1.05–1.10; p < 0.001) but not induced PTDs. Conclusions: Spontaneous PTD is more common during the summer and its rate is declining steadily over the past decades. Increased outdoor temperature has a significant effect on the incidence of spontaneous, but not induced, PTD.

Original languageEnglish
Pages (from-to)2483-2487
Number of pages5
JournalJournal of Maternal-Fetal and Neonatal Medicine
Issue number20
StatePublished - 18 Oct 2017


  • Preterm birth
  • risk factors
  • summer
  • time-series analysis
  • variation

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health
  • Obstetrics and Gynecology


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