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Table 1 PTB by different groups of characteristics, pregnancy history and GWG

From: Rate of gestational weight gain and preterm birth in relation to prepregnancy body mass indices and trimester: a follow-up study in China

Variables

N (%)

Mean (SDa)

OR (95 % CIb)

P value

Total

17475

   

Districts

 Hebei

2871 (16.4)

 

reference

 

 Liaoning

1039 (5.9)

 

1.56 (1.12,2.16)

0.008

 Xiamen

2080 (11.9)

 

0.64 (0.45,0.89)

0.009

 Hunan

5294 (30.3)

 

0.82 (0.64,1.05)

0.119

 Sichuan

1839 (10.5)

 

0.90 (0.66,1.24)

0.522

 Yunnan

4352 (24.9)

 

0.99 (0.77,1.27)

0.911

Type of residents

 Local

16847 (96.4)

 

reference

 

 Non-local

628 (3.6)

 

0.49 (0.27,0.90)

0.021

Maternal race/ethnicity

 Han

16485 (94.3)

 

reference

 

 Other

990 (5.7)

 

1.50 (1.11,2.03)

0.008

Maternal education

  < =Junior high school

7060 (40.4)

 

reference

 

 Senior high school

3850 (22.0)

 

0.89 (0.72,1.11)

0.299

 College or graduate school

3567 (20.4)

 

0.90 (0.73,1.13)

0.365

 Missing

2998 (17.2)

 

0.81 (0.64,1.04)

0.093

 Maternal age

 

26.7 (4.3)

  

  < 25

5633 (32.2)

 

reference

 

 25–35

10863 (62.2)

 

1.10 (0.92,1.32)

0.308

  > = 35

979 (5.6)

 

1.89 (1.39,2.58)

<0.001

 Maternal pre-pregnancy BMI (kg/m2)

 

20.7 (3.1)

  

 Underweight (<18.5)

4335 (24.8)

 

1.16 (0.96,2.00)

0.129

 Normal (18.5–24.9)

11559 (66.1)

 

reference

 

 Overweight (25.0–30.0)

1347 (7.7)

 

1.30 (0.98,1.73)

0.072

 Obese (> = 30.0)

234 (1.3)

 

1.48 (0.80,2.74)

0.210

Parity

 Nulliparous

10001 (62.2)

 

reference

 

 Multiparous

5098 (29.2)

 

1.04 (0.86,1.25)

0.696

 Missing

2376 (13.6)

 

1.08 (0.85,1.37)

0.547

Infant sex

 Male

9241 (52.9)

 

reference

 

 Female

8234 (47.1)

 

0.87 (0.74,1.02)

0.094

 Rates of weight gain (2nd and 3rd trimester) (kg/week)

 

0.56 (0.19)

  

 Insufficient

2298 (12.5)

 

1.46 (1.12,1.92)

0.006

 Adequate

5054 (28.9)

 

reference

 

 Excessive

10123 (57.9)

 

1.38 (1.13,1.68)

0.002

 Gestational age at delivery (weeks)

 

39.0 (1.3)

  

 Full-Term

16874 (96.6)

   

 Preterm

601 (3.4)

   
  1. aSD, Standard Deviation
  2. b95 % CI, 95 % confidence interval