Geographical Differences in Preterm delivery rates in Sweden: A population-based Cohort Study

Sarah R. Murray, Julius Juodakis, Jonas Bacelis, Anna Sand, Jane E. Norman, Verena Sengpiel, Bo Jacobsson

Research output: Contribution to journalArticlepeer-review


Introduction Preterm delivery is a major global public health challenge. The objective of this study was to determine how the preterm delivery rates differ throughout a country of very high human‐development index and to explore rural versus urban environmental and socio‐economic factors which might be responsible for this variation. Material and methods A population‐based study was performed using data from the Swedish Medical Birth Register 1998 to 2013. Sweden was chosen as a model because of its validated routinely collected data and availability of individual social data. The total population comprised 1 335 802 singleton births. Multiple linear regression was used to adjust gestational age for known risk factors (maternal smoking, ethnicity, maternal education, maternal age, height, fetal gender, maternal diabetes, maternal hypertension and parity). A second and a third model were subsequently fitted allowing separate intercepts for each municipality (as fixed or random effects). Adjusted gestational ages were converted to preterm delivery rates and mapped to maternal residential municipalities. Additionally, the effects of six rural versus urban environmental and socio‐economic factors on gestational age were tested using simple weighted linear regression. Results The study population preterm delivery rate was 4.12%. Marked differences from the overall preterm delivery rate were observed (rate estimates ranged from 1.73% ‐ 6.31%). Statistical significance of this heterogeneity across municipalities was confirmed by a chi‐squared test (p<0.001). Around 20% of the gestational age variance explained by the full model (after adjustment for known variables described above) could be attributed to municipality‐level effects. In addition, gestational age was found to be longer in areas with higher fraction of built upon land and other urban features. Conclusions After adjusting for known risk factors large geographical differences in rates of preterm delivery remain. Additional analyses to look at the effect of environmental and socio‐economic factors on gestational age revealed an increased gestational age in urban areas. Future research strategies could focus on investigating the urbanity effect to try to explain the preterm delivery variation across countries with a very high human‐development index.
Original languageEnglish
JournalActa Obstetricia et Gynecologica Scandinavica
Early online date31 Aug 2018
Publication statusE-pub ahead of print - 31 Aug 2018


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