IntroductionMany anatomic and physiologic changes occur in women's bodies during pregnancy which make them vulnerable both physically and mentally (1). Depression during pregnancy is the fourth disability factor in the world and it is predicted that it will become the second disability factor by 2020 (2). The relationship between depression history and postpartum depression has been shown which may be followed by adverse consequences such as suicide and child abuse (3,4). Depression rate is remarkable especially in second and third trimester of pregnancy (5). The results of a study showed that pregnancy depression increases the likelihood of cesarean delivery to 2.3 times. The probability of low birth weight is higher in depressed women along with lower mean birth weight and head circumference in infants of depressed mothers (6). Women sleep quality changes during their reproductive years due to hormonal variations at menstrual cycle, pregnancy and menopause periods (7). Sleep disorder is one of the most common complaints during pregnancy which may be due to physiological, hormonal, cardiovascular and metabolic changes including endocrine changes such as increased levels of progesterone and prolactin, increased size and movements of fetus, distended bladder, diaphragm rise and stomach ache (8,9). Also, fatigue, urinary frequency, husband smoking and education may cause sleep disruption (10). Twenty-five percent of women face with sleep disorder in the first trimester of pregnancy and this rate reaches to 75% in the third quarter (11,12). It has been found that people with insomnia or severe sleep disorders during pregnancy will have cesarean compared to those who do not have these problems (13). Sleep disorder also may lead to psychological changes. Evidence has indicated that sleep patterns are the predictive factors for postpartum depression (14). The relationship between poor quality sleep and postpartum depression has been found and significant positive correlation has been reported between sleep quality score in the third trimester of pregnancy and postpartum depression (15). Also, relationship between sleep quality and depression has been reported in pregnant women at 14 weeks of pregnancy age (16). A study results showed that pregnant women sleep time is not more than non-pregnant women despite their increased time in bed; the number Abstract Objectives: Many anatomic and physiologic changes occur in women's bodies during pregnancy that make them vulnerable both physically and mentally. Depression is a common disorder that can be accompanied with obstetric, neonatal and postnatal complications. This study aimed to determine the relationship between depression and sleep quality among pregnant women in Tabriz-Iran, 2014. Materials and Methods: This cross-sectional study was conducted on 565 pregnant women who referred to Tabriz health centers by 2-stage cluster sampling. The data were collected using socio-demographic questionnaire, Edinburgh Postnatal Depression Scale (EPDS) and Pittsburgh Sleep Quality In...