Risk of uterine leiomyomata with menstrual and reproductive factors in premenopausal women: Korea nurses’ health study

Table 4 Association between selected menstrual and reproductive factors and uterine leiomyomata risk among women reporting recent gynecologic examination

Characteristics (N = 2,924)	Person-years	Cases	Age-adjusted HR (95% CI)	Multivariate HR (96% CI)
Menarche age, years^a
≤ 11	568	11	1.16 (0.62–2.17)	1.19 (0.64–2.23)
12–13	5445	99	Reference	Reference
14–15	5498	69	0.65 (0.48–0.89)	0.70 (0.51–0.96)
≥ 16	1179	9	0.39 (0.20–0.77)	0.40 (0.20–0.79)
P for trend			< 0.001	0.001
Menstrual cycle length^b
Cycle length, days
< 26	910	19	1.25 (0.77–2.02)	1.26 (0.77–2.05)
26–31	7271	120	Reference	Reference
32–39	2672	39	0.94 (0.65–1.35)	0.91 (0.63–1.31)
≥ 40 or too irregular to estimate	948	7	0.49 (0.23–1.05)	0.48 (0.22–1.03)
P for trend			0.04	0.03
Cycle length ages 18–22 years, days
< 26	788	12	0.91 (0.51–1.64)	0.92 (0.51–1.67)
26–31	7933	138	Reference	Reference
32–39	2420	25	0.61 (0.40–0.93)	0.62 (0.40–0.95)
≥ 40 or too irregular to estimate	1472	12	0.48 (0.27–0.87)	0.49 (0.27–0.89)
P for trend			0.007	0.008
Parity^c
Nulliparous	5365	87	Reference	Reference
Parous	7326	101	0.51 (0.35–0.73)	0.52 (0.36–0.76)
Age at first birth, years
≤ 28	2253	41	Reference	Reference
29–30	1607	16	0.61 (0.34–1.08)	0.62 (0.34–1.11)
≥ 31	2353	32	0.75 (0.47–1.19)	0.70 (0.44–1.12)
P for trend			0.263	0.157
Attempting to conceive (≥ 1 year)^d
No	11,213	174	Reference	Reference
Yes	1479	14	0.59 (0.34–1.01)	0.62 (0.36–1.08)
Oral contraceptive use (≥ 2 months)^d
No	11,631	178	Reference	Reference
Yes	1057	10	0.69 (0.37–1.32)	0.76 (0.40–1.45)

^aAdjusted for age at baseline, menstrual cycle length, parity history, body mass index, and systolic blood pressure
^bAdjusted for age at baseline, age at menarche, parity history, body mass index, and systolic blood pressure
^cAdjusted for age at baseline, age at menarche, menstrual cycle length, body mass index, and systolic blood pressure
^dAdjusted for age at baseline, age at menarche, menstrual cycle length, parity history, body mass index, and systolic blood pressure
CI, confidence interval; HR, hazard ratio

ISSN: 1472-6874