Table 5.

Estimated Risk of Lung Cancer Among Women by Age at First Birth^a (n = 1,459), Lung Cancer Susceptibility Study, Boston, Massachusetts, 1992–2004

Age at First Birth, years	Cases (n = 683)		Controls (n = 776)		Adjusted Odds Ratiob	95% Confidence Interval
	No.	%	No.	%
Nulliparous	149	22	117	15	1	Referent
<20	90	13	95	12	0.55	0.35, 0.85
20–24	268	39	303	39	0.48	0.34, 0.68
25–29	115	17	184	24	0.43	0.29, 0.64
≥30	61	9	77	10	0.60	0.36, 0.99

^aParticipants enrolled in the study between 1992 and 2002 had data collected on age at first birth.

^bAdjusted for age, smoking status, pack-years of smoking, years since quitting smoking, and number of children.