Access to high-quality maternal health care services is limited in Kenya, which resulted in ~36,000 maternal and neonatal deaths in 2018. To tackle this challenge, our collaborating non-governmental organization (NGO) which works on maternal health in Kenya, developed PROMPTS, an SMS based tele-triage system for pregnant and puerperal women which has more than 350,000 active users in Kenya. PROMPTS empowers pregnant women living far away from doctors and hospitals to send SMS messages to get quick answers (through human helpdesk agents) to questions about their medical symptoms and pregnancy status. Unfortunately, ~1.1 million SMS messages are received by PROMPTS every month, which makes it challenging for helpdesk agents to ensure that these messages can be interpreted correctly and evaluated by their level of emergency to ensure timely responses and/or treatments for women in need. This paper reports on a collaborative effort with an NGO to develop a state-of-the-art natural language processing (NLP) framework, TRIM-AI (TRIage for Mothers using AI), which can automatically predict the emergency level (or severity of medical condition) of a pregnant mother based on the content of their SMS messages. TRIM-AI leverages recent advances in multi-lingual pre-training and continual pre-training to tackle code-mixed SMS messages (between English and Swahili), and achieves a weighted F_1 score of 0.774 on real-world datasets. TRIM-AI has been successfully deployed in the field since June 2022, and is being used by our collaborating NGO to prioritize the provision of services and care to pregnant women with the most critical medical conditions. Our preliminary A-B tests in the field show that TRIM-AI is ~17% more accurate at predicting high-risk medical conditions from SMS messages sent by pregnant Kenyan mothers, which reduces the helpdesk's workload by ~12%.