Association of newborn Apgar score with maternal admission to the intensive care unit

Introduction — The newborn Apgar score efficiently evaluates a baby's condition at birth, and its need for immediate attention. The risk of neonatal/infant death is greatest at a low 5-minute Apgar score of 0-3, and moderate at an intermediate score of 4-6, compared to a normal Apgar score of 7-10. The risk neonatal and maternal mortality is highest when both mother and child are admitted to an ICU after delivery. Since the newborn 5-minute Apgar score is routinely collected, we assessed its association with maternal admission to ICU.

Methods — We included 712,715 singleton obstetrical livebirths in Ontario, 2006-2012, after excluding 99,735 births (12.3%) with missing or ineligible data. We explored how a low, intermediate or normal newborn APGAR at 5 minutes is associated with maternal postpartum admission to ICU. Modified Poisson regression generated unadjusted and adjusted relative risks (aRR), controlling for maternal age, parity, income quintile, pre-pregnancy diabetes mellitus, obesity, drug dependence/tobacco use, and newborn sex. Results were stratified by preterm (24-36 weeks) vs. term (37+ weeks) delivery, the hypertensive disorders of pregnancy (HDP — gestational hypertension or preeclampsia), and those above vs. below the median time interval between delivery and ICU admission. We secondarily evaluated ICU admission with concomitant mechanical ventilation – an indicator of greater ICU severity (Damon Scales, personal communication). The study was approved by the Sunnbybrook Health Sciences Centre Research Ethics Board.

Results — Compared to mothers whose newborn had a normal 5-minute Apgar score (1.7 per 1000), the rate of maternal ICU was 13.0 per 1000 with an intermediate score and 18.8 per 1000 with a low score. The rates of ICU were high in women with preterm delivery or HDP, but the aRRs were more pronounced for term births or in the absence of HDP. The aRRs were also higher among women admitted to ICU within 4 hours of delivery, and especially, for women also requiring mechanical ventilation.

Discussion — A low 5-minute newborn Apgar score reflects a higher risk of maternal ICU, with and without mechanical ventilation. Existing clinical models of severe acute maternal morbidity (SAMM) have moderate discrimination for predicting maternal end-organ injury or death within 30 days postpartum (C statistic 0.66, 95% CI 0.65-0.67). In high-resource settings, maternal admission to ICU is a reasonable proxy for SAMM. A logical step is to evaluate whether the newborn Apgar score improves the discriminative performance of predictive models for SAMM, within a few hours of delivery and over the conventional 42-day postpartum period, and within high- and low-resource settings.