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Table 3 Incident and recurrent preterm birth in the second pregnancy according to change in the number of prenatal visits between the first and the second pregnancies, 2001–2015 (n = 1,764,025)

From: Differences in risk factors for incident and recurrent preterm birth: a population-based linkage of 3.5 million births from the CIDACS birth cohort

First and second pregnancy variables Incident preterm birth Recurrent preterm birth Pdifference b
n (%) ORa 95% CI n (%) ORa 95% CI
≥ 4 prenatal visits
 Yes-Yes 83,212 (73.35) Ref Ref 14,148 (62.19) Ref Ref <0.00
 Yes-No 18,762 (16.54) 2.57 2.52–2.62 3324 (14.61) 2.25 2.14–2.37  
 No-Yes 6920 (6.10) 1.14 1.11–1.18 3246 (14.27) 1.01 0.96–1.05  
 No-No 4553 (4.01) 2.22 2.14–2.30 2033 (8.94) 2.20 2.06–2.38  
  1. aAdjusted analysis by mother’s residence area, household overcrowding, mother’s self-declared race/skin color, mother’s level of education, mother's marital status, maternal age, type of delivery in the second birth
  2. bPdifference represents the interaction between incident and recurrent preterm birth for the respective characteristic. The equation for this model is as follows: Logit [ Pr (PTB2=1/Risk factors)] = β0 + β1 (PTB1) + β2 (risk factor X2) + β3 (PTB1) × (risk factor X2), where PTB1 and PTB2 are indicators of a preterm birth in the first and second pregnancy, respectively