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Table 4 Initiation of preconceptional folic acid supplementation and risk of spontaneous preterm delivery (sPTD)

From: Folic acid supplementation, dietary folate intake during pregnancy and risk for spontaneous preterm delivery: a prospective observational cohort study

sPTD

Initiation of folic acid supplementation

 

Unadjusted

Adjusted 1

Adjusted 2

  

n

HR

(CI)

p

HR

(CI)

p

HR

(CI)

p

All

No

964

1

  

1

  

1

  
 

0-8 w preconception

313

0.93

(0.82; 1.06)

0.28

0.99

(0.87; 1.13)

0.89

1.01

(0.88; 1.16)

0.88

 

>8 w preconception

478

1.15

(1.03; 1.29)

0.01

1.18

(1.05; 1.32)

0.005

1.20

(1.06; 1.36)

0.004

Early

No

169

1

  

1

  

1

  
 

0-8 w preconception

57

0.97

(0.72; 1.31)

0.84

1.07

(0.79; 1.45)

0.67

1.04

(0.76; 1.43)

0.81

 

>8 w preconception

108

1.48

(1.16; 1.89)

0.001

1.60

(1.24; 2.06)

<0.001

1.55

(1.18; 2.05)

0.002

Late

No

795

1

  

1

  

1

  
 

0-8 w preconception

256

0.92

(0.80; 1.06)

0.23

0.97

(0.84; 1.11)

0.63

0.99

(0.86; 1.15)

0.93

 

>8 w preconception

370

1.08

(0.96; 1.22)

0.22

1.09

(0.96; 1.24)

0.19

1.12

(0.98; 1.29)

0.11

  1. Initiation of preconceptional folic acid supplementation (Q1 data) and hazard ratios (HR) for spontaneous PTD (n = 1,755 for 22+0-36+6 weeks, n = 334 for early (22+0-33+6 weeks), n = 1,421 for late (34+0-36+6 weeks)). Cox regression for 66,014 participants in the Norwegian Mother and Child Cohort Study (2002 – 2009). Iatrogenic deliveries have been censored in the regression model.
  2. 1Cox regression, adjusted for maternal age, prepregnancy BMI, parity, history of PTD and spontaneous abortion, child's sex, smoking habits and alcohol consumption during pregnancy, maternal education, marital status, household income, energy intake and dietary folate intake.
  3. 2Adjustment as above as well as for first-trimester folic acid supplementation and preconceptional and first-trimester vitamin A supplementation.