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

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)

First and second pregnancy variables	Incident preterm birth			Recurrent preterm birth			P_difference ^b
First and second pregnancy variables	n (%)	OR^a	95% CI	n (%)	OR^a	95% CI	P_difference ^b
≥ 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

^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
^bP_difference 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

ISSN: 1741-7015