Pregnancy as a sensitive period has a critical effect on the mother and infant's life. It is well understood that dietary habits and mother awareness can improve health status and prevent pregnancy complications such as gestational diabetes, pre-eclampsia, and nausea and vomiting. The current study was conducted to investigate the association between dietary habits and self-care behaviors with pregnancy complications. This cross-sectional study was conducted across 300 pregnant women in their third trimester referred to healthcare centers and Yas hospital in Tehran, Iran. Dietary habits and self-care behaviors were assessed by valid and reliable questionnaires. Dietary intake and physical activity were evaluated using valid and reliable Food Frequency Questionnaires and Pregnancy Physical Activity questionnaires, respectively. Women with self-care behaviors had a lower rate of pre-eclampsia (P = 0.9). Regarding food habits, pregnant women who ate their meals faster had a non-significantly higher rate of gestational diabetes and pre-eclampsia. Pregnant women who consumed red meat on a daily frequency had a significantly higher rate of nausea and vomiting (OR 1.85; 95% CI 1.05-3.28, P = 0.03). Also, there was a significant positive association between the mother's pre-pregnancy BMI and gestational diabetes and pre-eclampsia [(OR 2.03; 95% CI 1.03-3.98, P = 0.03) and (OR 4.23; 95% CI 1.12-16.0, P = 0.03) respectively]. There was no significant association between pregnant women's dietary habits and GDM and pre-eclampsia. However, pregnant women with pre-pregnancy overweight and obesity had increased odds of gestational diabetes and pre-eclampsia significantly.