Background: Currently, diabetes mellitus (DM) is considered as one of the top health problemsrnof the World. The World Health Organization (WHO) estimated that, globally, hyperglycemia isrnthe third highest risk factor for premature mortality, next to high blood pressure and tobacco use.rnWorld estimate of 8.8% (415 million) adults aged 20-79 affected by DM in 2015 with littlerngender difference and in the same year the estimate of hyperglycemia in pregnancy in Africa wasrn10.5% affecting 3.3 million live births. Its burden is increasing and the largest increase will takernplace in low and middle-income countries. The magnitude of diabetes is nearly equal amongrnboth sexes but it uniquely affects women through its impact during pregnancy. Today as manyrnas 60 million women of reproductive age have type 2 diabetes and gestational diabetes mellitusrn(GDM), affects up to 15% of pregnant women worldwide. Poorly controlled diabetes isrnimportant cause of maternal and fetal complications among pregnant mothers. Earlyrnidentification, close monitoring and management of diabetes mellitus among pregnant womenrncan meaningfully improve pregnancy and birth outcome. In Ethiopia, although diabetes mellitusrnis recognized as one of the major non-communicable diseases, the burden among pregnantrnwomen and its effect on pregnancy and birth outcomes are not well researched. rnObjective: To assess the magnitude of DM and its effect on maternal and birth outcomes amongrnpregnant mothers in Wolaita Zone, Southern Ethiopia rnMethods: This study has been undertaken in Wolaita Zone, Southern Ethiopia. Institution-basedrnretrospective document review with a cross-sectional design, cross-sectional study andrnretrospective cohort study designs were employed respectively to determine magnitude of preexistingrnrndiabetes, prevalence of GDM and effect of diabetes on pregnancy and birth outcomernamong mothers receiving maternity services in selected health facilities in Wolaita Zone.rnQualitative study was done to explore detection and management modalities of GDM. The studyrntook place from August 2017 to June 2018. The study populations were pregnant mothers andrnhealth care providers. Data were collected by document review or data extraction, interviewingrnof pregnant women by structured questionnaire, and in-depth interview of health professionalsrnengaged in maternity care. Oral glucose tolerance test was performed and GDM was diagnosedrnbased on WHO criteria. rnData were entered in to Epi Info version 7 and analysis was done by STATA version 14. rnDescriptive statistics was computed and data were presented using figures and tables. Chi-squarernand corresponding p-value were determined to assess the association between dependent andrnindependent variables for the first objective. Binary logistic regression was applied to show thernassociation of independent variables with dependent variables. Thematic analysis approach wasrnused to analyze qualitative data using NVIVO version 12. The study was approved byrnInstitutional Review Board of College of Health Sciences, Addis Ababa University. rn Results: Magnitude of pre-existing DM among mothers receiving maternity care within onernyear period was 2.8% 95% CI (1.5, 4.2). The magnitudes among urban and rural residents werern3.3% and 1.4% respectively. Pre-existing diabetes mellitus was significantly associated withrnfamily history of diabetes (Chi square 24.8, P-value, 0.001). Previous history of spontaneousrnabortion (aOR:rn5.3; 95%CI: 1.6-17.4rn) and fetal macrosomia (aOR: rn3.9; 95%CI: 1.2-13.1rn), werernidentified to be significantly associated with pre-existing diabetes. rnPrevalence of GDM was 4.2% (95% CI, 2.5, 6.2) with mean post glucose load level of 160.1rnmg/dl (6.3) and 15(4%) among urban residents and 7(4.9%) among rural residents. Thernproportion of GDM increases with increase in number of pregnancies. Previous history ofrnspontaneous abortion (aOR:rn 3.5; 95%CI: 1.7-14.6rn) and family history of type II diabetes (aOR:rn 4.3;rn95%CI: 1.3-8.7rn) were significantly associated with GDM. rnMothers with DM were 2.9 times more likely to be delivered by caesarean section than nondiabeticrnmothersrn(aRR:rn2.9,rn95%CI:rn1.3-6.2)rnandrnthernriskrnofrnpre-termrndeliveryrnisrn2.5rntimesrnhigherrnrnamongrnmothersrnwith DM,rn(aRR:rn2.5, 95% CI:rn1.1-6.2).rnrnScreening of women for GDM was done by selective screening within 24-28 weeks ofrngestational age. The participants also mentioned that they made diagnosis of GDM based onrnWHO criteria. Health care providers use dietary modification, exercise and drug treatment torntreat GDM. Participants confirmed that lack of standard guidelines and protocols, lack ofrnattention of mid-level workers to screen GDM, inadequate trained health care providers, shortagernof supplies and equipment and late antenatal care visits were barriers to detection andrnmanagement of GDM. rnConclusions and Recommendations: The magnitude of pre-existing DM is almost the same asrnthat of International Diabetes Federation estimate to Ethiopia. Family history of diabetes is foundrnto be associated with pre-existing DM. Pre-existing diabetes is associated with increased risk ofrnabortion and fetal macrosomia. The prevalence of GDM is higher compared to other studiesrnconducted in the country. Diabetes mellitus among pregnant mothers is associated with increasedrnrisk of pre-term birth and caesarean section delivery. Commonly reported challenges to detectrnGDM among mothers were lack of standard guidelines and protocols, lack of trained health carernproviders, shortage of supplies and equipment and late antenatal care visits. rnStrengthening screening, care and prevention strategies for gestational diabetes mellitus are rnimportant to improve maternal and child health. Early detection and management of diabetes rnmellitus should be one of the key activities to improve maternal and child mortality andrnmorbidity. Policy makers and health care leadership need to address challenges for detectionrnand management of GDM, by strengthening the health care system by availing standardrnguidelines and protocols, providing on job training for mid-level health care providers, fulfillingrnsupplies and consumables and working on early antenatal visits of pregnant mothers. Nationalrnlarge scale study is important to estimate the burden of DM among pregnant mothers and itsrneffect on maternal and birth outcomes at national level.