Background: Antenatal depression is a significant form of depression that can arise during pregnancy, is characterized by mood disorders, and is considered as one of the main reasons for maternal mortality and morbidity. Depression during pregnancy can result in premature birth, a lower birth weight, preeclampsia and many other comorbidities for mother and babies. In Oman, maternal depression is not routinely screened for during pregnancy nor after childbirth. Aim: The aim of this study is to explore the prevalence of depression among Omani mothers during the antenatal and to determine the adverse birth outcomes associated with antenatal depression. Method: A longitudinal design was used to achieve the aim of the current study. Omani pregnant women (n=263) from Al Dhahira region were screened for antenatal and postnatal depression, using the Edinburg Postnatal Depression Scale (EPDS). The questionnaire was administered twice per participant; during antenatal visits, and again at the postpartum follow-up visit (usually at week 2 and 6 postpartum). Women's sociodemographic, economic, and obstetric characteristics were reported followed by the EPDS questionnaire. All parts of the instrument were self-administered except for the birth outcomes which were collected from the medical records. The hypotheses were tested using independent t-test, Chi-square, and ANOVA. Characteristics of the participants using descriptive analyses (mean, standard deviation, frequency and percentage) were tested and described before conducting correlation analysis to examine the associations between antenatal depression and adverse birth outcomes (controlling for sociodemographic and obstetric confounders). Result: The prevalence of antenatal depression was 22.4% of the mothers and the postnatal depression in 25.9%. The mean age for mothers who had depression was 30 (SD=4.8) with no significant difference from the other groups. Furthermore, among mothers who had depression; 61.0% were housewives, 62.7% had middle monthly income of 500-1000 RO/month, and 25.4% had lower monthly income (<500 RO/month). Besides, 54.2% of mothers with depression had higher education, 55.9% lived in simple family construction, and 86.4% were physically inactive. Moreover, among the group of mothers who had depression; 25.4% did not plan their pregnancies and 55.9% were not using contraception before the current pregnancy. The antenatal depression was significantly and positively associated with postnatal depression (P<0.01) but not with the other adverse birth outcomes (gestational age at delivery (P= 0.18), Apgar score 1 minute after birth (P=0.30), Apgar score 5 minutes after birth (P=0.15), weight of the infant at birth (P=0.13), onset of delivery (P= 0.72 ),initiation of breastfeeding (P= 0.81), intrapartum complications (P= 0.19), type of induction (P=0.47), mode of delivery (P=0.92 ) and perineum status (P=0.61). Conclusion: A considerable rate of pregnant mothers had antenatal depression which was slightly increased after childbirth. Furthermore, the antenatal depression was only associated with the postnatal depression and not the other adverse outcomes. The findings of this study highlight the urgent need for standardization of depression screening of all pregnant women in the Sultanate. It also calls for a population-based study to investigate the prevalence of depression in pregnant women and in the first year following childbirth. Furthermore, midwives and other health care professionals who provide services to pregnant women should be aware of the high prevalence of antenatal depression. Hence, training may be required to ensure midwives' competency in psychosocial assessment, including the use of reliable screening tools (e.g., the EPDS), as well as the management of women suffering from antenatal and/or postnatal depression.