Background Unintended pregnancy at a young age can lead to poor reproductive health, social and economic outcomes. The high rate of unintended teenage pregnancies in Tanzania is indicative of inadequate availability and uptake of modern contraception. Determining trends and determinants of unmet need for modern contraception among adolescent girls and young women (AGYW) in Tanzania will help address the burden of unintended pregnancies. Methodology An analytical cross-sectional study design was conducted using secondary data from three consecutive Tanzania Demographic and Health Surveys (TDHS) 2004/05, 2010 and 2015/6. Data analysis was performed using Stata version 15.0. Data analysis considered the complex survey design. Categorical and continuous variables were summarized using descriptive statistics. Poisson regression model was used to determine factors associated with unmet need for modern contraception. Results A steady decline in unmet need for modern contraception was observed from 31.8% in 2004/05 to 27.5% in 2015/16 survey. In the multivariable analysis, higher prevalence of unmet need for modern contraception was observed among adolescents, participants with at least one live birth, from poor wealth tertile, and those sexually active during the past four weeks. Conclusion Despite declining levels, the unmet need for modern contraception among young women in Tanzania remains high. AGYW under 19 years, those from poor households, and those who are postpartum are most at risk. Greater efforts are required to meet the reproductive health needs and rights of these sub-groups of AGYW in order to facilitate uptake of modern contraceptives and therefore reducing the risk of unintended pregnancies and unmet need for modern contraception.

The authors have declared no competing interest.

This study was supported through the DELTAS Africa Initiative SSACAB. The DELTAS Africa Initiative is an independent funding scheme of the African Academy of Sciences (AAS) Alliance for Accelerating Excellence in Science in Africa (AESA) and is supported by the New Partnership for Africa’s Development Planning and Coordinating Agency (NEPAD Agency) with funding from the Wellcome Trust and the UK government. The views expressed in this publication are those of the authors and not necessarily those of the AAS, NEPAD Agency, Wellcome Trust or the UK government.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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Ethical approval to carry out the study was obtained from Tumaini University, KCMUCo Research and Ethical Committee (# PG016/2019). Permission to use DHS data was granted from the DHS MEASURE program. The TDHS has ethical approval from ICF Institutional Review Board (IRB) as well as from local IRB in Tanzania and written informed consent was obtained from all the study participants above 18 years of age. For each participant under 18 years of age written informed consent was obtained from the parent/guardian.

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Data are available from https://dhsprogram.com/Data/. DHS data may be accessed through registration of a research project on the DHS website and requesting access to data. This is the same manner the authors obtained access to the data. The authors did not have any special access privileges to DHS data