Given the significant role of low birth weight (LBW) in infant death and disability and relevant childhood diseases, the present systematic review was conducted to determine the factors affecting newborns’ birth weight in Iran.

This study systematically reviewed all the observational studies carried out in Iran between 1990 and 2021 (retrieval date: April 28, 2021) in four steps and through searches in Persian databases (including Magiran, SID, and IranDoc) and English databases (including Embase, Cochrane Library, Web of Sciences, Google Scholar, PubMed, and Scopus). All the relevant articles were searched by two researchers separately and collected using research keywords, Boolean operators, and a combination of relevant tags depending on the type of database. The quality of the articles was evaluated with 22-item Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) and Ottawa checklists, respectively.

Of the 251 articles collected, 31 met the study inclusion criteria. Variables such as the mother’s age (35%), body mass index (BMI) (25%), preterm childbirth, and diagnosis with a maternal chronic disease (25%) were found to be the most common causes of LBW in the reviewed studies, by order of prevalence.

Based on the results of this review study and given that many of the known risk factors of LBW are preventable, the timely diagnosis, proper treatment, and follow-up of women at risk can prevent the birth of LBW infants.