Characteristic | 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^{*} | |||

Maternal | |||||

Age, yr, mean ± SD | 30.2 ± 6.0 | 30.7 ± 5.9 | 31.3 ± 5.8 | < 0.001 | < 0.001 |

Hypertension | n = 14 750 | n = 15 200 | n = 19 524 | 0.07 | 0.1 |

2676 (18.1) | 2912 (19.2) | 3681 (18.9) | |||

Prenatal care | n = 14 440 | n = 14 577 | n = 19 307 | < 0.001 | < 0.001 |

14 080 (97.5) | 14 314 (98.2) | 18 702 (96.9) | |||

Chorioamnionitis | n = 13 678 | n = 12 183 | n = 14 758 | < 0.001 | < 0.001 |

1764 (12.9) | 2115 (17.4) | 3081 (20.9) | |||

Infant | |||||

Gestational age, wk, median (IQR) | 29 (27–31) | 30 (27–31) | 30 (27–31) | 0.9 | > 0.9 |

Gestational age group, wk | < 0.001 | ||||

23–25 | 1729 (11.5) | 1906 (12.1) | 2630 (13.1) | ||

26–28 | 4101 (27.2) | 4014 (25.6) | 5042 (25.1) | ||

29–32 | 9230 (61.3) | 9772 (62.3) | 12 407 (61.8) | ||

Birth weight, g, mean ± SD | 1324 ± 451 | 1328 ± 454 | 1325 ± 454 | 0.7 | 0.8 |

Sex, male | n = 15 036 | n = 15 671 | n = 20 054 | 0.005 | 0.02 |

8031 (53.4) | 8645 (55.2) | 10 989 (54.8) | |||

Singleton | n = 15 008 | n = 15 683 | 14 038 (69.9) | 0.001 | 0.02 |

10 338 (68.9) | 10 679 (68.1) | ||||

Small for gestational age | n = 15 037 | n = 15 680 | n = 20 059 | 0.6 | 0.3 |

1429 (9.5) | 1530 (9.8) | 1971 (9.8) | |||

Minor congenital malformation | 2423 (16.1) | 2472 (15.8) | 3249 (16.2) | 0.5 | 0.8 |

SNAP-II score > 20 | n = 15 051 | n = 15 546 | n = 19 900 | < 0.001 | < 0.001 |

2690 (17.9) | 2527 (16.3) | 2954 (14.8) |

Note: IQR = interquartile range, SD = standard deviation, SNAP = Score for Neonatal Acute Physiology.

↵* Unless stated otherwise.

↵† The

*p*value for differences between the 3 epochs were obtained using the χ^{2}test for categorical variables and*F*test or Kruskal–Wallis test as appropriate.↵‡ The

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