Table 1 Characteristics of women born in southeastern China between 1955 and 1985 by 5-year birth cohort

Age at menarche (yrs), mean (SD)

15.7 (1.5)

15.5 (1.39)

15.1 (1.3)

14.9 (1.3)

14.8 (1.2)

14.7 (1.2)

<0.0001^*

<0.0001^†

Age at registration (yrs), mean (SD)

36.2 (2.6)

32.3 (2.25)

27.3 (3.3)

25.1 (2.6)

24.4 (2.0)

22.3 (1.1)

<0.0001^*

<0.0001^†

Region, n (%)

<0.0001^‡

<0.0001^¶

Urban

847 (11.9)

3 902 (7.3)

39 698 (12.8)

51 565 (13.9)

58 740 (16.9)

9 127 (11.6)

Rural

6 281 (88.1)

49 343 (92.7)

269 681 (87.2)

318 406 (86.1)

289 616 (83.1)

69 913 (88.5)

Education, n (%)

<0.0001^‡

<0.0001^§

High school or above

876 (12.3)

6 195 (11.67)

52 373 (17.0)

78 738 (21.3)

124 960 (35.9)

25 420 (32.3)

Middle school

2 151 (30.3)

25 278 (47.60)

167 684 (54.4)

232 677 (63.0)

200 758 (57.7)

49 501 (62.8)

Primary school or less

4 076 (57.4)

21 634 (40.5)

88 225 (28.6)

57 768 (15.7)

22 152 (6.4)

3 897 (4.9)

Medical health history, n (%)

<0.0001^‡

<0.0001^¶

No chronic diseases

6 854 (96.2)

51 096 (96.0)

298 418 (96.5)

360 774 (97.5)

343 415 (98.6)

78 453 (99.3)

At least one chronic disease

274 (3.8)

2 149 (4.0)

10 961 (3.5)

9 197 (2.5)

4 941 (1.4)

587 (0.7)