[Accuracy of gestational age assessment in Brazilian Information System on Live Birth (SINASC): a population study].

The prevalence of preterm births has shown a growing trend in many countries, including developed ones. Studies in Brazil have shown that the Information System on Live Births (SINASC, in Portuguese), until 2010, underestimated the prevalence of preterm births, when compared with studies based on primary data. Starting in 2011, gestational age at birth has been calculated in SINASC according to the last menstrual period (LMP), when available.