Outcome | No. (%) of infants | p value for epochs^{†} | p value for linear trend^{‡} | ||
---|---|---|---|---|---|

Epoch 1 (2004–2008)n = 15 060^{*} | Epoch 2 (2009–2012)n = 15 692^{*} | Epoch 3 (2013–2017)n = 20 079^{*} | |||

Survival without major morbidity | 9035 (60.0) | 10 063 (64.1) | 13 886 (69.2) | < 0.001 | < 0.001 |

Bronchopulmonary dysplasia | n = 14 129 | n = 14 721 | n = 18 954 | < 0.001 | < 0.001 |

2937 (20.8) | 2665 (18.1) | 2862 (15.1) | |||

Severe neurologic injury | n = 11 593 | n = 12 775 | n = 16 531 | < 0.001 | < 0.001 |

1531 (13.2) | 1559 (12.2) | 1804 (10.9) | |||

Necrotizing enterocolitis | n = 14 920 | n = 15 634 | n = 20 067 | 0.001 | < 0.001 |

716 (4.8) | 728 (4.7) | 805 (4.0) | |||

Severe retinopathy of prematurity | n = 6605 | n = 6464 | n = 8533 | < 0.001 | < 0.001 |

760 (11.5) | 641 (9.9) | 793 (9.3) | |||

Early-onset sepsis | 202 (1.3) | 218 (1.4) | 342 (1.7) | 0.007 | < 0.001 |

Late-onset sepsis | 2616 (17.4) | 2248 (14.3) | 2212 (11.0) | < 0.001 | < 0.001 |

Survival | 14 027 (93.1) | 14 629 (93.2) | 18 866 (94.0) | 0.002 | 0.001 |

↵* Unless stated otherwise.

↵† The

*p*value for differences between the 3 epochs were obtained using the χ^{2}test.↵‡ The

*p*value for linear trend was for 2004–2017. Significance was assessed using the Wald χ^{2}test from logistic regression models using 1-year periods as an independent continuous variable.