Table 2.

Fecundability Ratios According to Baseline and Time-Varying Electronic Cigarette Use, Pregnancy Study Online, United States and Canada, 2017–2020

			Unadjusted		Adjusted a
Exposure	No. of Pregnancies	No. of Cycles	FR	95% CI	FR	95% CI
Baseline e-cigarette use
Never e-cigarette user	2,238	11,997	1.00	Referent	1.00	Referent
Ever e-cigarette user	366	2,492	0.82	0.74, 0.91	0.88	0.78, 0.99
Former e-cigarette user	289	1,945	0.83	0.74, 0.93	0.89	0.78, 1.00
Current e-cigarette user	77	547	0.79	0.63, 0.99	0.85	0.68, 1.07
E-liquid, mL/dayb
<3	41	292	0.76	0.54, 1.07	0.82	0.58, 1.15
≥3	36	255	0.82	0.61, 1.11	0.89	0.65, 1.21
Time-varying e-cigarette use
Never e-cigarette user	2,232	11,944	1.00	Referent	1.00	Referent
Ever e-cigarette user	372	2,545	0.82	0.74, 0.91	0.88	0.78, 0.99
Former e-cigarette user	286	1,921	0.84	0.75, 0.94	0.89	0.79, 1.01
Current e-cigarette user	86	624	0.78	0.63, 0.97	0.84	0.67, 1.06
Time-varying e-cigarette use among never cigarette smokersc
Never e-cigarette user	1,898	10,031	1.00	Referent	1.00	Referent
Ever e-cigarette user	141	880	0.85	0.72, 1.00	0.90	0.76, 1.07
Former e-cigarette user	119	731	0.86	0.72, 1.02	0.91	0.76, 1.08
Current e-cigarette user	22	149	0.79	0.51, 1.21	0.87	0.57, 1.32

Abbreviations: CI, confidence interval; e-cigarette, electronic cigarette; FR, fecundability ratio.

^a Adjusted for age, annual household income, education, baseline smoking status, pack-years of cigarette smoking, weekly alcohol intake, intercourse frequency, doing anything to improve conception chances, body mass index, Major Depression Inventory score, multivitamin or supplement use, Healthy Eating Index, and parity.

^b Question on mL of liquid/day asked only on baseline questionnaire.

^c Includes 3,432 women who had never smoked cigarettes by the end of follow-up. Model adjusted for all variables listed under footnote a, except for baseline smoking status and pack-years of cigarette smoking.