Table 1 Descriptive variables for the 81 606 women included in the analysis

From: Determinants of age at menarche in the UK: analyses from the Breakthrough Generations Study

Variables

Numbers and completeness of reporting

Description of variable

Continuous variables

N (%) reporting

N (%) missing

Median (range)

Age at menarche, years

81 606 (100.0)

0 (0)

13 (7, 20)a

Age at entry, years

81 606 (100.0)

0 (0)

46 (16, 98)

Birthweight, g

56 678 (69.5)

24 928 (30.5)

3318 (734, 5958)

Maternal age at birth, years

77 336 (94.8)

4270 (5.2)

27 (12, 50)

Number of weeks breastfedb

9278 (11.4)

72 328 (88.6)

12 (0, 265)

Childhood exercise, h per week

77 796 (95.3)

3810 (4.7)

2 (0, 56)

Number of siblings

80 523 (98.7)

1083 (1.3)

1 (0, 13)

Birth order

75 541 (92.6)

6065 (7.4)

0 (0, 12)

Categorical variables

N (%) reporting

N (%) missing

N (%) in each category

Twinning

80 567 (98.7)

1039 (1.3)

 

 Singleton

  

78 989 (98.0)

 Same-sex dizygotic twin

  

526 (0.7)

 Opposite-sex dizygotic twin

  

587 (0.7)

 Monozygotic twin

  

465 (0.6)

Pre-eclampsia or eclampsia c

67 545 (82.8)

14 061 (17.2)

 

 Not exposed

  

64 375 (95.3)

 Exposed

  

3170 (4.7)

Maternal smoking c,d

6340 (7.8)

75 266 (92.2)

 

 Not exposed

  

5710 (90.1)

 Exposed

  

630 (9.9)

Ethnicity

81 438 (99.8)

168 (0.2)

 

 White

  

80 468 (98.8)

 Mixed white/non-white

  

327 (0.4)

 Non-whitee

  

643 (0.8)

Weight at age 7 years compared with peers

80 335 (98.4)

1271 (0.2)

 

 Much thinner

  

3363 (4.2)

 A little thinner

  

17 246 (21.5)

 About the same

  

49 110 (61.1)

 A little heavier

  

9492 (11.8)

 Much heavier

  

1124 (1.4)

Height at age 7 years compared with peers

79 656 (97.6)

1950 (0.2)

 

 Much shorter

  

2431 (3.1)

 A little shorter

  

13 725 (17.2)

 About the same

  

41 444 (52.0)

 A little taller

  

17 949 (22.5)

 Much taller

  

4107 (5.2)

Vegetarian before age 8 years

81 416 (99.8)

190 (0.2)

 

 No

  

81 107 (99.6)

 Yes

  

309 (0.4)

  1. aOnly three subjects reached menarche at age 7 years and six subjects at age 20 years.
  2. bA large amount of data were missing for this variable because it was only available if the mother was also a study participant.
  3. cPrenatal exposure to these factors.
  4. A large amount of data were missing for this variable because it was only available if the mother was also a study participant and the subject was a first-born child.
  5. eThe largest non-white ethnic group was Indian women (33.2%) followed by women who classed themselves as Black-Caribbean (17.3%).
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