Unexposed group (n=493,496) No. of participants (%) Exposed group (n=101,900) No. of participants0 (%)
χ2
P
Maternal age (years)
<24 50255 (10.2) 8412 (8.3) 660.24 <0.001
24–26 81222 (16.5) 15864 (15.6)
27–29 118040 (23.9) 23723 (23.3)
30–32 102817 (20.8) 23585 (23.1)
33–35 72330 (14.7) 16094 (15.8)
>35 68832 (13.9) 14222 (13.9)
Residential city
Guangzhou 19850 (4.0) 2970 (2.9) 1193.80 <0.001
Dongguan 34579 (7.0) 5641 (5.5)
Jiangmen 18107 (3.7) 3303 (3.3)
Shenzhen 75334 (15.3) 13280 (13.0)
Foshan 345626 (70.0) 76706 (75.3)
Infant sex <0.01 0.950
Male 263153 (53.3) 54349 (53.3)
Female 230343 (46.7) 47551 (46.7)
Pregnancy complications (N=173064)*
Hypertensive disorders of pregnancy (HDP) 96.57 <0.001
No 143933 (97.3) 24369 (96.7)
Yes 3937 (2.7) 825 (2.3)
Gestational hypertension 971 (0.7) 252 (1.0)
Pre-eclampsia / Eclampsia
2712 (1.8)
473 (1.9)
Chronic hypertension
141 (0.1)
44 (0.2)
Chronic hypertension with superimposed pre-eclampsia
113 (0.1)
56 (0.2)
Gestational diabetes mellitus (GDM) 183.64 <0.001
No 129653 (87.7) 21313 (84.6)
Yes 18217 (12.3) 3881 (15.4)
Preterm birth 15.58 <0.001
No 467865 (94.8) 96307 (94.5)
Yes 25631 (5.2) 5593 (5.5)
Very premature (<32 GWs) 2121 (0.4) 443 (0.4)
Moderate/late premature (32-36 GWs) 23510 (4.8) 5150 (5.1)
Stillbirth (N=595904) 3.36 0.067
No 493496 (99.92) 101900 (99.90)
Yes 405 (0.08) 103 (0.10)
Marital status 472.03 <0.001
Married 488376 (99.0) 100631 (98.8)
Unmarried 4263 (0.8) 732 (0.7)
Other 857 (0.2) 537 (0.5)
Parity 2121.60 <0.001
0 (Primiparas) 415074 (84.1) 79686 (78.2)
1 (Multiparas) 63158 (12.8) 17603 (17.3)
2-4 (Multiparas) 15264 (3.1) 4611 (4.5)
Delivery type 1871.40 <0.001
Natural delivery 297591 (60.3) 63394 (62.2)
Operative vaginal delivery 16735 (3.4) 1055 (1.0)
Cesarean delivery 179027 (36.3) 37298 (36.6)
Other 143 (<0.1) 153 (0.2)
Mean±SD Mean±SD t P
Maternal age (years) 29.78±5.09 30.07±4.94 17.11 <0.001
Gestational length (week Mean ± SD) 38.74±1.46 38.66±1.46 16.22 <0.001