Survey on seasonal variation in the frequency of preterm births in the city of Rafsanjan in 2011-2012

Seasonal variations in incidence of diseases can be reason of effect of environmental factors on health. Since the seasonal pattern in preterm birth varies across countries and because of importance of preterm births and unknown causes of it, this study was designed to investigate the frequency of preterm births in different seasons.

This cross-sectional study used data of all 5,860 infants born in the Rafsanjan Nik-Nafs hospital in 2011-2012. Inclusion criteria included live birth more than 2 weeks gestational age and birth weight more than 500 grams. Gestational age was determined according to mother's last menstrual period date. The criterion for preterm birth was gestational age less than 37 weeks gestation. Data was collected through delivery records of hospital medical documentary unit. For data analysis, chi-square and Fisher's exact tests was used.

The prevalence of preterm birth in this study was 6.96% (408 cases). The highest and the lowest frequency of preterm births were in January and February, respectively (P 0.031). Also, preterm births was most frequent in spring (8.4%) and it was least frequent in winter 4.9%) (P=0.002). The difference in frequency of preterm births in varying seasons across natural deliveries, Afghan race and boys was found statistically significant (P<0.05).

The results of our study showed that preterm birth increase in the warm seasons of the year and it is necessary for health care systems, as well as nursing and midwifery services to take appropriate action in these circumstances.