Table 1

Distribution of menstrual regularity at age of 18–22 years old by year of birth
Year of birth
1930s 1940s 1950s 1960s 1970s 1980s
n (%) n (%) n (%) n (%) n (%) n (%)
Menstrual regularity
Very regular 42 (42) 1664 (38) 5935 (38) 6933 (34) 1965 (30) 55 (20)
Usually regular 32 (32) 1772 (40) 6090 (39) 7855 (39) 2468 (38) 126 (45)
Usually irregular 19 (19) 661 (15) 2365 (15) 3815 (19) 1386 (21) 69 (25)
Always irregular 6 (6) 282 (6) 1013 (7) 1559 (8) 622 (10) 28 (10)
No periods 2 (2) 39 (1) 118 (1) 193 (1) 78 (1) 2 (1)

Kruskal-Wallis test χ2 = 312.0, p < .0001.

Hosokawa et al.

Hosokawa et al. BMC Women's Health 2012 12:19   doi:10.1186/1472-6874-12-19

Open Data