Data collection and analysis: Descriptive statistics describe characteristics and results.

Main results: Thirty-two papers relating to 26 core outcome sets were included (maternal: 18 papers: 17 COS; neonatal: 14 papers: 9 COS). Fifteen (58%) were published since 2017. No included COS met all minimum standards for development. All COS met the minimum standard for scope. Eighteen (69%) met all three minimum standards for stakeholder involvement. No included COS met all five minimum standards for consensus process. COS included between 6 and 56 outcomes. Two COS (8%) provided recommendations for how and when to measure outcomes.
Conclusions: This is the first application of COS-STAD minimum standards relevant to maternal and neonatal health. Findings offer a baseline evaluation. There is an urgent need to address outcomes, measurement and timing in core outcomes to support harmonisation between core outcome sets.