Background: Although the prevention of unintended pregnancy has been the major rationale for family planning and reproductive health programs throughout the world, a significant level of unintended pregnancy still exists in almost all countries of the world. The highest rate of unintended pregnancy occurs in Sub-Saharan Africa, where maternal and child mortality rates are also the highest. Unintended pregnancy has a number of costs to women including abortion related maternal deaths, as well as to the unwanted child in terms of health and development. Few studies have examined the effects of unintended pregnancy on maternal and child health and well-being in developing countries including Ethiopia. Objectives: The aims to examine the effects of unintended pregnancies on maternal and child health and health behavior in Gilgel Gibe Demographic Surveillance area, Jimma zone, southwest Ethiopia. Methods: The study is designed as a mixed method study in which both quantitative and qualitative data collection and analysis were employed. The quantitative study involved a follow up study among pregnant women and a cross-sectional survey among women with a live birth in the two years before the survey respectively. The prospective cohort study was conducted among 622 pregnant women, identified from the 11 Demographic Surveillance Site (DSS) villages, who were followed from pregnancy through to delivery. Baseline survey was conducted in June and July 2012 to collect data on pregnancy intention, depressive symptoms, social support and other variables. Birth weight was measured within 72 hours of birth to examine the effects of pregnancy intention and related maternal health behaviors on birth weight. Moreover, a cross-sectional survey among 1370 women who have had a birth in the two years before the survey was conducted to assess the associations of pregnancy intention and related fertility behaviors on maternal and child health care and child survival. Women with live births in the two years before the survey were randomly selected from the 11 kebeles in the DSS. A qualitative study is included to describe the context and results that emerge from the quantitative study. Eight focus group discussions were conducted with women disaggregated by place of residence and parity. Quantitative data were entered to EPI Data and analysed using STATA version 11. Analysis involved descriptive measures and multivariate regression analysis. Odds ratio, relative risk, incidence rate ratio , 95% CI and P values were used to interpret results. The qualitative data was transcribed verbatim, translated and analysed using a content analysis approach Results: The level of unintended pregnancy of 35% [95% CI, 32.5-37.5] in the cross-sectional study and 41% [95% CI, 37.1 - 44.9] in the baseline prospective study is high. Older women, rural women, women with no formal education, high parity women and women with low decision making autonomy were more likely to report unintended pregnancy. The major causes of unintended pregnancy were non-use of contraception, xii inconsistent use and method failure. In the qualitative study, participants mentioned that unintended pregnancy most often occurs because women hesitate to use contraceptives due to fear of side effects or because they discontinue a method. Use of maternal health services is very low in the study area. Only 42% of women used any antenatal care (ANC) for the index pregnancy and 12% delivered at a health facility. Only 13% of women started ANC in the first trimester and 17% made the recommended four or more ANC visits. A higher proportion of women with intended pregnancies reported use of maternal health care than women with unintended pregnancies. At the multivariate level, the odds of using ANC was significantly lower among women with unintended pregnancies (OR, 0.76, 95% CI; 0.58-0.98) compared to women with intended pregnancies. Moreover, compared to women with intended pregnancies, the odds of receiving adequate ANC was significantly lower (RR, 0.67, 95%CI; 0.46-.96) among women with unintended pregnancies. The association with institutional delivery was attenuated after adjusting for other socio-demographic factors. Using the Edinburgh Postpartum Depression Scale (EPDS) and a cut of point of 13 and above, it was found that 19.9% (95% CI, 16.8-23.1) of pregnant women who participated in the follow up study had high symptoms of depression. Substantial variation was observed in the magnitude of EPDS with pregnancy intention, food security status, intimate partner violence, social support and history of pregnancy loss. At the multivariate level, the odds of being depressed were nearly twice higher (OR, 1.96, 95% CI; 1.09-3.54) among women with unwanted pregnancy compared to women with a wanted pregnancy. Similarly, the odds of having depressive symptoms were higher among women from food insecure households, women who experienced intimate partner physical violence during pregnancy, and women with low social support compared with their counter parts. Of the 622 women included in the follow up study, birth outcomes of 612 women were identified and birth weights of 537 births were measured within 72 hours after birth. Ninety six percent of the pregnancies ended in a live birth. The mean birth weight was 2989 grams (SD± 504 grams). Among the 537 neonates whose birth weight was taken, the incidence of LBW was 17.9%, (95% CI; 14.6, 21.1). A higher proportion of low birth weight neonates were born to women aged 35 and above (26%), women in lowest wealth tertile (25.4%) and to women with unwanted pregnancy (28.4%). The multivariate log binomial regression also showed that the risk of low birth weight was two times higher (RR, 2.08; 95% CI, 1.02-4.23) among births after unwanted pregnancy compared to births from wanted pregnancy. The other factors that were significantly associated with LBW in the final model were wealth status, ANC use and maternal mid upper arm circumference (MUAC) size. xiii There were 1382 births among 1370 women who participated in the cross-sectional survey. Although 74.3% of children alive at the time of the survey had received at least one type of vaccinations, only 37% (95% CI, 33.5-39.9) of children age 12-24 months received all basic childhood vaccinations. About one quarter, 24% [95% CI; 21.8-26.4], of children had experienced illness during the two weeks before the survey. Among the children with any illness, 59.2% (95% CI, 53.8-64.7) had received treatment and advice from health facilities. Among the 1382 children born in the two years before the survey, there were 78 deaths showing a mortality rate of 51 per 1000 person years [95% CI, 40.4-63.1].There were no significant differences between intended and unintended births in terms of receiving vaccinations or mortality in the first two years but intended births were more likely to receive treatment up on illness than unintended births. At the multivariate level, there was a significant effect of unintended pregnancy on treatment seeking (RR, 1.56 95%, CI: 1.09-2.33) but corresponding effects on vaccination and mortality were not observed. Conclusion: There is a high level of unintended pregnancy in the study area particularly among rural, older, the poor and uneducated women. Unintended pregnancy is linked to a wide range of maternal and child health issues; including use of antenatal care, maternal depression during pregnancy, child health care and birth weight. Recommendations: Given the high level of unintended pregnancy, improving access to family planning information and services is essential to improve the health of women, children and families. It is important to build on the current momentum of expanding access to family planning in Ethiopia to help women and families achieve their desired family size. Efforts should be made to increase access to more effective and long acting family planning methods. Similarly, improving use of maternal and child health services in rural areas is important. Increasing awareness of the importance of healthy timing, spacing and limiting of pregnancies, and on maternal and child health seeking behavior - early pregnancy symptoms, early initiation of ANC, health facility delivery, completing childhood vaccinations and care seeking for childhood illness – is important. Improving the integration of services - family planning and maternal and child health services, and family planning and maternal and child health issues in to other development programs such as food security is also essential. Further research is required to understand the reasons for under-utilization of maternal and child services in the study area, and on the feasibility and modes of service integration. Key words: Unintended pregnancy, unwanted pregnancy, birth interval, maternal health, depression, social support, vaccination, low birth weight, Gilgel Gibe, DSS