Table I.

Characteristics of the study population and association with TTP: the Maternal-Infant Research on Environmental Chemicals (MIREC) study.

Continuous variables	n	Mean (SD)a	Median	Minimum	Maximum	P value**
Maternal age (years)	1743	32.83 (4.96)	32.74	18.34	46.35	<0.001
Paternal age (years)	1510	34.78 (5.68)	34.51	18.66	58.74	<0.001
Age difference (years)	1510	1.80 (3.98)	1.00	−15	26	0.18
Gestational age (weeks)	1741	12 (1.52)	12.43	6	14	0.19
Categorical variables	n	%	TTP (months)
			Mean (SD)a	Median (p25–p75)
Education
Some college or less	236	13.5	5.8 (12.8)	1 (1–5)		0.46
College diploma	399	22.9	5.2 (8.9)	2 (1–5)
Undergraduate	644	37.0	5.7 (12.2)	2 (1–5)
Graduate (MSc PhD)	464	26.6	4.3 (6.4)	2 (1–4)
Country of birth
Canada	1412	81.0	5.3 (10.8)	2 (1–5)		0.93
USA	27	1.5	4.7 (6.4)	2 (1–6)
Mexico	8	0.5	5.1 (4.8)	4.5 (1–9)
China	17	1.0	3.8 (4.8)	1 (1–5)
Other	279	16.0	5.1 (8.4)	2 (1–6)
Household income
<$60 000	361	20.7	4.5 (10.1)	2 (1–4)		0.06
$60 001–100 000	609	35.0	5.2 (9.9)	2 (1–5)
>$100 000	691	39.6	5.7 (10.7)	2 (1–6)
No response	82	4.7	5.2 (10.9)	2 (1–4)
Parity conditional on gravidity
No prior pregnancy	501	28.8	6.5 (13.7)	2 (1–6)		<0.001
Prior pregnancy without live birth(s)	270	15.5	6.8 (12.1)	2 (1–6)
Prior pregnancy with live birth(s)	971	55.7	4.2 (7.2)	2 (1–4)
Maternal smoking
Never	1077	62.9	5.1 (8.9)	2 (1–5)		0.85
Former	392	22.5	5.3 (11.8)	2 (1–5)
Currentb	272	15.6	5.7 (13.1)	2 (1–4)
Pre-pregnancy BMI (kg/m2)
<24.9	1034	63.6	4.9 (9.6)	2 (1–5)		0.003
25–29.9	355	21.9	5.2 (11.4)	2 (1–4)
>30	236	14.5	6.7 (11.3)	3 (1–7)
Current paternal smoking
No	1217	83.0	5.2 (9.9)	2 (1–5)		0.83
Yes	249	17.0	5.6 (12.0)	2 (1–5)

BMI, body mass index.

^aArithmetic mean and SD.

^bWomen who stopped during pregnancy or 1 year before.

**P-values for the association with TTP: likelihood ratio for continuous variables, log-rank test for categorical variables.