Table 1 Baseline perinatal and neonatal characteristics of infants with NRF according to birth weight

Gestational age (week)

33.4 ± 3.6

27.8 ± 1.9^*

30 ± 1.8^*

32.9 ± 1.8^*

37.5 ± 2.2

39.2 ± 1.6^*

< 0.001

BW (g)

2105 ± 840

859 ± 100^*

1274 ± 140^*

1941 ± 285^*

3088 ± 403

4365 ± 477^*

< 0.001

Male, n (%)

3347(59.9)

175(56)^*

650(54.8)^*

1438(59.1)^*

999(64.9)

85(73.3)

< 0.001

Cesarean delivery, n(%)

3664(65.60)

158(50.60)^*

711(59.90)^*

1688(69.30)

1081(66.20)

89(76.70)

< 0.001

Fetal distress, n(%)

564(11.2)

34(12.6)

112(11.0)^*

206(9.2)^*

193(13.8)

19(3.8)

< 0.001

Congenital anomalies, n(%)

103(1.8%)

11(3.5%)

18(1.5%)

39(1.6%)

32(2%)

3(2.5%)

0.127

Antenatal steroid use^a, n(%)

1594(33.2)

126(46.8)^*

519(51.0)^*

830(39.5)^*

117(8.9)

2(2.0)^*

< 0.001

Gestational diabetes, n(%)

907(16.2)

39(12.5)

205(17.2)

381(15.6)

240(15.6)

42(36.2)^*

< 0.001

Gestational hypertension, n(%)

770(13.7)

89(28.5)^*

226(19)^*

328(13.4)^*

117(7.6)

10(8.6)

< 0.001

Premature rupture of membrane > 24 h, n(%)

550(9.8)

31(9.9)^*

159(13.4)^*

288(11.8)^*

67(4.3)

5(4.3)

< 0.001

Apgar score at 1 min

8(7, 9)

6(4, 8)^*

8(6, 8)^*

8(7, 9)^*

9(8, 9)

8(7, 9)^*

< 0.001

Apgar score at 5 min

9(8, 10)

8(6, 9)^*

8(8, 9)^*

9(8, 10)^*

9(8, 10)

9(8, 10)

< 0.001

PS in delivery room, n(%)

54(0.9)

4(1.2)

19(1.6)

18(0.7)

12(0.7)

1(0.8)

0.127

Positive pressure ventilation in the delivery room, n(%)

1096(19.6)

105(33.6)^*

295(24.8)^*

420(17.2)

252(16.3)

24(20.6)

< 0.001

Endotracheal intubation in delivery room, n(%)

475(8.5)

81(25.9)^*

114(9.6)^*

129(5.3)^*

138(8.9)

13(11.2)

< 0.001

Chest compressions in the delivery room, n(%)

235(4.2)

29(9.2)^*

62(5.2)

68(2.7)^*

64(4.1)

12(10.3)^*

< 0.001