One Continuum, Two Ledgers: Cause-Paired Maternal and Neonatal Mortality Across 26 Locations, with a Post-Hoc 204-Country Inequality Extension, 1990–2023

Introduction: Whether maternal and neonatal mortality decline in lockstep determines where obstetric and newborn programmes should co-invest, yet global estimates report them separately. We paired maternal and neonatal causes along a priori care pathways in the Global Burden of Disease Study 2023 (GBD 2023) to test whether they share causes, places and margins.Methods: We develop a dyad synchrony index (DSI) for cause-paired co-movement, analysing deaths from 10 maternal causes (females aged 10–54; six key years) and five neonatal causes (ages 0–27 days), 1990–2023, across 21 GBD regions and five SDI quintiles (n=26 locations, the primary analysis), plus a post-hoc inequality extension over a purpose-built 204-country GBD 2023 extraction (1990, 2023). Three pathway pairs were pre-registered (maternal sepsis×neonatal sepsis; obstructed labour×birth asphyxia; hypertensive disorders×preterm birth). Synchrony used Spearman concordance; declines were decomposed into exposure and fatality margins, and best-frontier avoidable deaths computed.Results: Maternal deaths fell from 422,924 (1990) to 239,929 (166,628–334,199)* in 2023 (−43.3%); neonatal five-cause deaths from 2,841,581 to 1,474,021 (1,168,225–1,840,930*; −48.1%). All three pairs were level-concordant (r≈0.91–0.93), largely reflecting the shared development gradient; synchrony evidence lay in co-movement of change: 1990–2023 declines (Spearman ρ 0.77, 0.57, 0.80) and first differences (ρ 0.58, 0.49, 0.62; p≤2.3×10⁻⁹). Declines ran predominantly on the fatality margin (95.2% of the obstructed-labour decline; exposure contributed 10.9% of the preterm-birth decline). At the 2023 best-SDI frontier, 92.2% (region-frontier sensitivity 97.8%) of maternal direct-cause deaths and 73.5% (sensitivity 92.8%) of neonatal deaths were avoidable (upper bound). Central Asia was the extreme orphan pathway: maternal infection deaths fell 70.2% while neonatal sepsis deaths rose 62.2%.Conclusions: Maternal and neonatal mortality share causes, places and margins; most of the joint toll is avoidable at already-observed performance, and orphan pathways mark where dyad logic breaks. Ending Preventable Maternal Mortality (EPMM) and the Every Newborn Action Plan (ENAP) should be monitored as one dyad with two targets.