TABLE 4.

Association of frequency of night shifts per month and menstrual‐related variables in women with three rotating shifts

	Frequency of night shifts per month	Model 1		Model 2
		PR	95% CI	PR	95% CI
Irregular cycles	None	Reference		Reference
	≤5 nights	1.84	1.29‐2.61	1.93	1.29‐2.89
	6‐7 nights	1.47	0.95‐2.29	1.51	0.92‐2.48
	≥8 nights	1.14	0.79‐1.64	1.24	0.81‐1.89
Amenorrhea ≥3 mo	None	Reference		Reference
	≤5 nights	2.50	0.94‐6.65	3.84	1.21‐12.22
	6‐7 nights	1.70	0.52‐5.59	2.07	0.58‐7.47
	≥8 nights	0.45	0.10‐1.99	0.75	0.15‐3.66
Abnormal menstrual period	None	Reference		Reference
	≤5 nights	0.76	0.24‐2.43	0.74	0.22‐2.50
	6‐7 nights	1.72	0.70‐4.19	1.55	0.53‐4.51
	≥8 nights	1.41	0.69‐2.89	1.32	0.60‐2.89
Dysmenorrhea or premenstrual symptoms affected their work	None	Reference		Reference
	≤5 nights	1.09	0.90‐1.33	1.19	0.96‐1.48
	6‐7 nights	0.91	0.69‐1.20	0.98	0.73‐1.33
	≥8 nights	1.12	0.96‐1.31	1.23	1.02‐1.49
Often affected	None	Reference		Reference
	≤5 nights	0.77	0.31‐1.93	1.00	0.36‐2.74
	6‐7 nights	0.98	0.43‐2.24	1.20	0.47‐3.06
	≥8 nights	1.51	0.90‐2.53	1.93	1.03‐3.61

Model 1: adjusted for age. Model 2: adjusted for age, body mass index, and hospital size, and the department in which women worked.

Abbreviations: CI, confidence interval; PR, prevalence ratio.