Time of day/unit busyness at birth and perinatal hypoxia and or moderate to severe hypoxic ischemic encephalopathy a cohort study

Objectives: To investigate the potential link between nighttime births, unit busyness, and the incidence of perinatal hypoxia or moderate-to-severe hypoxic-ischemic encephalopathy. Methods: Retrospective cohort study with nested case control study of all singleton births >= 35-week gestation for the years 2010-20, in Alberta, a province of Canada. Perinatal Hypoxia was defined as intrapartum stillbirth or neonatal death from asphyxia or Neonatal Intensive Care Unit admission and at least two of the following: a. Apgar score of <= 5 at 10 min; b. mechanical ventilation or chest compressions for resuscitation within 10 min; c. cord pH < 7.00 (venous or arterial), or arterial base deficit >= 12 at birth. Moderate-severe hypoxic ischemic encephalopathy was defined as per Sarnat criteria. Nighttime birth was defined as between 2000 and 0559 h. Unit busyness was characterized by number of births by site per shift and was described by quartiles. Results: The risk of perinatal hypoxia was higher for nighttime births, risk difference 0.5/1000 births, 95% confidence interval (0.2-0.8), but moderate-severe hypoxic ischemic encephalopathy was not, risk difference 0.2/1000 births 95% confidence interval (0.0-0.3). We did not observe an increase in the risk of perinatal hypoxia or moderate-severe hypoxic ischemic encephalopathy with delivery in the highest quartile of unit busyness. Conclusions: We observed a small increase in the risk of birth with perinatal hypoxia for nighttime births but not for moderate-severe hypoxic ischemic encephalopathy. Neither perinatal hypoxia or moderate-severe hypoxic ischemic encephalopathy was associated with unit busyness.