Table 4.

Univariable and Multivariable Associations With Adherence Reported at Delivery

Variable	N	Crude	95% CI		P	Adjusted	95% CI		LRT
		βa	Lower	Upper		βa	Lower	Upper	P
Age (y)	957	0.01	−0.01	0.03	.154	—	—	—	—
Ethnicity
Other	27	−0.41	−1.07	0.25	.224	—	—	—	—
British–white	930	ref	—	—		—	—	—
Age full-time education finished
≤16	751	ref	—	—	.048	—	—	—	—
>16	206	0.27	0.00	0.53		—	—	—
Heaviness of smoking index (HSI)
0–3	631	ref	—	—	.026	ref	—	—	<.001
4–6	326	−0.26	−0.49	−0.03		−0.27	−0.50	−0.05
Partners’ smoking status
Nonsmoking	225	ref	—	—	.811	—	—	—	—
Smoking	654	0.08	−0.18	0.34		—	—	—
Not applicable	78	0.11	−0.34	0.55		—	—	—
Parity
≤1	649	ref	—	—	.654	—	—	—	—
2 or 3	256	−0.08	−0.33	0.17		—	—	—
≥4	52	0.14	−0.34	0.63		—	—	—
Baseline cotinine (ng × 10−1/ml)
12.1 (7.8–17.6), median (IQR)	957	−0.01	−0.03	0.00	.053	—	—	—	—
BMI
<18.5	28	0.10	−0.56	0.77	.228	—	—	—	—
18.5–24.9	362	ref	—	—		—	—	—
25–29.9	267	0.32	0.05	0.60		—	—	—
>30	254	0.10	−0.18	0.37		—	—	—
Missing	46	0.22	−0.31	0.75		—	—	—
Length of first behavioral support session
16–30	143	ref	—	—	.471	—	—	—	—
31–45	791	0.06	−0.25	0.36		—	—	—
>60	23	−0.38	−1.14	0.38		—	—	—
Previous preterm births
0	872	ref	—	—	.496	—	—	—	—
≥1	85	0.13	−0.25	0.52		—	—	—
Previous use of NRT
No	914	ref	—	—	.282	—	—	—	—
Yes	43	0.29	−0.24	0.82		—	—	—
Gestational age (wk)
12–19	766	ref	—	—	.963	—	—	—	—
20–24	191	0.01	−0.27	0.28		—	—	—
Treatment assignment
Placebo	483	ref	—	—	<.001	ref	—	—	<.001
NRT	474	0.50	0.29	0.72		0.51	0.29	0.72

BMI = body mass index; CI = confidence interval; LRT = likelihood ratio test; NRT = nicotine replacement therapy.

^aβ value and regression coefficients using square root transformed adherence.