PROJECT SUMMARY / ABSTRACT Obstructed labor accounts for 3-8% of all maternal deaths worldwide and, in many countries, is almost as prevalent today as it was 30 years ago. Cephalopelvic disproportion (CPD) is an inadequate size of the maternal pelvis, compared to the fetal head, which prevents the fetus from passing through the pelvic cavity during delivery, causing obstructed labor. CPD-related obstructed labor requires delivery via Caesarean section (C/S). CPD is especially prevalent in places like Ethiopia, where girls are small in stature, grow up malnourished, marry at a young age, or become pregnant before the pelvis is fully grown. Maternal and perinatal mortality in Ethiopia are among the highest in the world 7 and, 11% of maternal deaths are due to obstructed labor. The consequence of CPD-related obstructive labor (in the absence of C/S) is often maternal and/or perinatal mortality or morbidity; e.g., 1 in 250 women report having an obstetric fistula. Ethiopia has showing tremendous increases in the uptake of antenatal care and deliveries in health facilities over the past few years; yet, the rate of C/S remains very low (1.9%) due to the lack of infrastructure and surgical expertise and lack of timely assessment of the most at-risk mothers. In the Ethiopian public health sector, maternal care and delivery is provided at no cost, including making provisions for high-risk pregnancies to be transferred, lodged, and cared for to appropriate facilities. There is a pressing need to develop, and translate to clinical use, safe, affordable, easy-to-use, acceptable, and accurate methods to identify mothers at high-risk of obstructed labor, before the onset of labor, so high-risk mothers can be transferred to facilities where C/S is a viable option. The purpose of this proposal is to (i) validate risk scores over an adequately powered sample, over a broader range of gestational ages (12-42 weeks) and over 6 tribal regions in Ethiopia, (ii) to test the feasibility of introducing a low-cost, smartphone enabled ultrasound to improve CPD risk assessment in Ethiopia, (iii) quantify the context of use for the proposed intervention and improve ease-of-use and beneficiary acceptability of these CPD risk assessment tools, and (iv) identify and overcome barriers to CPD risk assessment and referral follow-up of high-risk mothers to primary hospitals, where C/S is an option. Successful realization of these aims will provide adequate validation, usability, acceptability, and first clinical use data for these novel CPD risk assessment tools in Ethiopia and position this innovation well for a broader clinical study to assess impact of integrating these tools across the primary health care sector in Ethiopia and, ultimately, integration into routine antenatal care. Further, with modest validation studies in other countries with a high CPD burden (e.g., Nigeria, India), this innovation can be translated to have a broader impact in saving lives at birth.