Table 5.

Hazard ratios (95% confidence intervals) for the association between preterm delivery in first pregnancy and CVD (MI and stroke) with and without adjustment for intermediate outcomes and the proportion of the association through the intermediates

	Term: ≥37 weeks (n=59,846)	Preterm:† <37 weeks (n=5,501)	Moderate Preterm:‡ ≥32 to <37 weeks (n=4,173)	Very Preterm:‡ <32 weeks (n=1,328)
Cases/Person-Years*	756/1,912,714	105/171,983	65/129,478	40/42,505
Model 1† Intermediate outcomes: Chronic Hypertension, Hypercholesterolemia, Type 2 Diabetes Mellitus, BMI
Without Intermediates§	1.00 (ref)	1.55 (1.27, 1.91)	1.29 (1.00, 1.66)	2.34 (1.82, 3.02)
With Intermediates∥	1.00 (ref)	1.47 (1.19, 1.80)	1.23 (0.96, 1.59)	2.12 (1.64, 2.73)
Proportion through Intermediates#	Ref	13.3% (7.9, 21.4)	17.1% (5.5, 42.5)	12.0% (8.6, 16.5)
Model 2a† Intermediate outcomes: Chronic Hypertension, Hypercholesterolemia, Type 2 Diabetes Mellitus, BMI
Without Intermediates§	1.00 (ref)	1.48 (1.21, 1.82)	1.26 (0.97, 1.62)	2.14 (1.66, 2.76)
With Intermediates∥	1.00 (ref)	1.41 (1.15, 1.73)	1.21 (0.94, 1.57)	1.94 (1.50, 2.50)
Proportion through Intermediates#	Ref	12.8% (7.1, 21.9)	14.5% (4.0, 41.1)	13.1% (9.0, 18.7)
Model 2b† Intermediate outcomes: Chronic Hypertension, Hypercholesterolemia, Type 2 Diabetes Mellitus, BMI, and Breastfeeding
Without Intermediates§	1.00 (ref)	1.48 (1.21, 1.82)	1.26 (0.97, 1.62)	2.14 (1.66, 2.76)
With Intermediates∥	1.00 (ref)	1.39 (1.14, 1.71)	1.20 (0.93, 1.55)	1.92 (1.49, 2.48)
Proportion through Intermediates#	Ref	15.9% (8.7, 27.3)	20.7% (5.5, 53.8)	14.0% (9.5, 20.1)

Model 1 is adjusted for age at first birth, age in 1989, race/ethnicity, and parental education

Model 2a is additionally adjusted for pre-pregnancy BMI, pre-pregnancy smoking, pre-pregnancy Alternative Healthy Eating Index (AHEI) score (in quintiles), pre-pregnancy alcohol intake, physical activity at age 18, pre-pregnancy oral contraceptive use, and family history of MI or stroke before age 60

Model 2b is the same as model 2a, but additionally includes breastfeeding as an intermediate outcome

^*Sample size and total case numbers differ from Table 2 due to additional exclusion criterion: pre-pregnancy chronic hypertension, type 2 diabetes mellitus, or hypercholesterolemia, missing BMI over follow-up, and missing date of diagnosis of risk factors on baseline questionnaire

^†Compares preterm (<37 weeks) to term (≥37 weeks)

^‡Preterm category is split into moderate preterm (≥32 to <37 weeks) and very preterm (<32 weeks)

^§Analogous to the total effect in causal mediation analysis,

^∥analogous to the direct effect in causal mediation analysis,

^#analogous to the proportion mediated in causal mediation analysis