Main effects of daily volume, weekend and hospital volume category on the odds of perinatal outcomes based on model 1*
| Outcome | High-volume day | Weekend | Volume category 1† | Volume category 2† | Volume category 3† |
|---|---|---|---|---|---|
| Maternal | |||||
| Obstetric infection | 1.01 (0.97 to 1.05) | 1.09 (1.05 to 1.13) | 0.93 (0.62 to 1.40) | 0.99 (0.69 to 1.43) | 1.02 (0.68 to 1.53) |
| Haemorrhage | 0.97 (0.93 to 1.00) | 1.05 (1.01 to 1.08) | 1.26 (0.86 to 1.85) | 1.08 (0.76 to 1.56) | 1.10 (0.73 to 1.65) |
| Severe perineal lacerations | 0.98 (0.94 to 1.01) | 1.08 (1.04 to 1.12) | 1.10 (0.93 to 1.30) | 1.06 (0.93 to 1.21) | 1.19 (1.04 to 1.36) |
| Prolonged LOS‡ | 1.05 (1.02 to 1.09) | 1.21 (1.17 to 1.25) | 1.03 (0.66 to 1.61) | 0.90 (0.66 to 1.24) | 0.85 (0.63 to 1.15) |
| Composite maternal | 1.00 (0.98 to 1.02) | 1.12 (1.10 to 1.15) | 1.09 (0.82 to 1.44) | 1.00 (0.79 to 1.26) | 1.01 (0.79 to 1.30) |
| Neonatal | |||||
| Birth trauma | 0.99 (0.96 to 1.03) | 0.99 (0.95 to 1.03) | 1.32 (0.86 to 2.03) | 1.03 (0.73 to 1.46) | 1.04 (0.73 to 1.48) |
| Neonatal seizures | 1.26 (1.01 to 1.57) | 1.04 (0.81 to 1.32) | 1.81 (1.27 to 2.58) | 1.69 (1.23 to 2.34) | 1.67 (1.23 to 2.27) |
| Apgar score <7 | 1.04 (0.97 to 1.12) | 1.14 (1.06 to 1.23) | 1.98 (1.46 to 2.67) | 1.36 (1.05 to 1.77) | 1.30 (1.00 to 1.69) |
| NICU admission | 0.99 (0.95 to 1.03) | 1.07 (1.04 to 1.11) | 0.82 (0.49 to 1.38) | 1.41 (0.87 to 2.29) | 1.33 (0.94 to 1.86) |
| Neonatal death | 0.88 (0.77 to 1.02) | 0.99 (0.85 to 1.14) | 1.31 (0.88 to 1.96) | 0.84 (0.63 to 1.12) | 1.04 (0.77 to 1.42) |
| Composite infant | 0.99 (0.96 to 1.02) | 1.04 (1.01 to 1.06) | 1.13 (0.79 to 1.62) | 1.24 (0.90 to 1.72) | 1.20 (0.92 to 1.56) |
Bold typeface indicates p<0.05.
*Results are OR (95% CI); models controlled for hospital volume category, maternal race/ethnicity, advanced maternal age, education, parity, insurance status, prenatal care and teaching hospital. Models estimated robust SEs accounting for hospital-level clustering.
†Hospital volume categories: category 1, 50–1119 annual births; category 2, 1200–2399 annual births; category 3, 2400–3599 annual births; as compared with referent, category 4, ≥3600 annual births.
‡Prolonged LOS defined as LOS >3 days for vaginal deliveries and >5 days for caesarean deliveries.
LOS, length of stay; NICU, neonatal intensive care unit.