Aims: The aim of the study was to investigate the effect of pre-pregnancy body mass index on weight gain during pregnancy. Methods and Material: This retrospective study was conducted on family medicine units in Turkey between March 2018 to September 2018. Pregnant files of the last 5 years were scanned and a questionnaire with 40 questions was filled. Results: 1061 pregnants from 72 provinces included in the study. Net weight difference during pregnancy was significantly higher in cesarean patients, in civil servants and in those with first pregnancy (p <0.05). Net weight difference was found to be significantly lower in those without education compared to other groups (p <0.05). Conclusions: Consequently, In conclusion, pre-pregnancy BMI and individual weight gain during pregnancy should be planned. Thus, many complications that may develop in mother and baby can be prevented. In this regard, benefiting from family medicine units that can reach all segments of the society and monitor pregnant women can increase their success rates. Key-words: Pregnancy, body mass index, gestational weight gain Key Messages: What’s already known about this topic? • According to various studies, nearly half of today’s pregnant women are overweight or obese • The body weight of the mother before pregnancy and the weight gained during pregnancy have an effect on pregnancy results. What does this article add? • Lifestyle changes required for ideal BMI should be planned in pre-pregnancy counseling. To achieve this, teams of family physicians, dieticians and individual sports trainers should be formed. • Those in the high risk group (eg, first pregnancy, uneducated and civil servant) should be monitored more frequently in terms of weight gain during pregnancy. • Personal and social information should be provided to correct false information that taking iron and multivitamin support during pregnancy causes weight gain.