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Table 1 Characteristics of the study sample(s)

From: Mediation of the effect of prenatal maternal smoking on time to natural menopause in daughters by birthweight-for-gestational-age z-score and breastfeeding duration: analysis of two UK birth cohorts born in 1958 and 1970

Sample characteristic

BCS70

(n = 3,878, followed-up to age 46 years)

NCDS

(n = 4,822, followed-up to age 50 years)

N

% complete cases

% imputed sample

 N

% complete cases

% imputed sample

Natural menopause

      

No

3,533

91.10

 

3,645

75.59

 

Surgical menopause

331

8.54

 

534

11.07

 

HT before FMP

174

4.49

 

542

11.24

 

Pre- and peri- menopause

3,028

78.07

 

2,569

53.28

 

Yes

345

8.90

 

1,177

24.41

 

Smoking in pregnancy

      

No

2,001

55.66

55.69

2,632

58.29

58.24

Yes (incl. stopped during pregnancy)

1,594

44.34

44.31

1,883

41.71

41.76

Missing

283

7.30

 

307

6.37

 

Birthweight (kg) (mean, SD)

3,607

3.26 (0.50)

 

4,423

3.26 (0.51)

 

Missing

180

4.75

 

399

8.27

 

Gestational age (weeks) (mean, SD)1

3,392

39.78

 

4,117

40.16 (1.73)

 

Missing

395

10.43

 

705

14.62

 

Birthweight z-score (mean, SD)

3,379

-0.21 (1.11)

-0.21 (1.19)

3,987

-0.36 (1.10)

-0.37 (1.20)

Missing

499

12.87

 

835

17.32

 

Breastfeeding

      

Never

1,877

59.63

59.74

1,285

30.48

30.51

Up to 1 month

507

16.11

16.14

1,031

24.45

24.55

More than 1 month

764

24.27

24.11

1,900

45.07

44.94

Missing

730

18.82

 

606

12.57

 

In school after age 15

      

Yes

1,342

37.47

37.42

1,229

26.96

27.01

No

2,240

62.53

62.58

3,330

73.04

72.99

Missing

296

7.63

 

263

5,45

 

Social class at birth

      

Non-manual

1,131

31.47

31.42

1,248

27.30

27.26

Manual

2,209

61.46

61.48

3,088

67.54

67.57

No father in HH/Other

254

7.07

7.10

236

5.16

5.17

Missing

284

7.32

 

250

5.18

 

Maternal age at birth (mean, SD)

3,609

25.94 (5.32)

25.95 (5.54)

4,568

27.49 (5.67)

27.48 (5.89)

Missing

269

6.94

 

258

5.27

 

Previous live births (mean, SD)

3,608

1.09 (1.29)

1.09 (1.32)

4572

1.26 (1.53)

1.26 (1.59)

Missing

270

6.96

 

254

5.18

 
  1. Note:
  2. 1 167 (4.92% of) women in BCS70 and 168 (4.08%) in NCDS were born before 37 weeks of gestation (preterm)
  3. The imputation model included birthweight z-score rather than birthweight (kg) and gestational age (weeks)
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