Table 1 Demographic and obstetric characteristics of mothers (n = 87,658) and infants (n = 88,424)

EPDS score at 1 month after birth^a

5.8

2.4

NVP status, n (%)^b

 No NVP

15,038

17.2

 Mild NVP

37,778

43.1

 Moderate NVP

25,276

28.8

 Severe NVP

9,566

10.9

Maternal age, years, n (%)^b

 ≤ 29

31,806

36.3

 ≥ 30

55,848

63.7

Marital status, n (%)^b

 Married

83,486

95.2

 Single/Divorced/widowed

3,491

3.7

Feelings about the pregnancy, n (%)^b

 Delighted

79,398

90.6

 Negative feelings

7,595

8.7

Parity, n (%) ^b

 Primipara

35,164

40.1

 Multipara

50,425

57.5

K6 score during mid/late pregnancy, n (%)^b

 ≤ 4

62,907

71.8

 ≥ 5

24,650

28.1

Maternal educational level, years, n (%)^b

 ≤ 12

30,451

34.7

 > 12

56,907

64.9

Paternal educational level, years, n (%)^b

 ≤ 12

37,326

42.6

 > 12

49,545

56.5

Maternal smoking status, n (%)^b

 Never a smoker

51,388

58.6

 Ex-smoker who quit before pregnancy

20,934

23.9

 Ex-smoker who quit during pregnancy

11,259

12.8

 Current smoker

3,446

3.9

Paternal smoking status, n (%)^b

 Never a smoker

24,155

27.6

 Ex-smoker who quit before pregnancy

20,433

23.3

 Ex-smoker who quit during pregnancy

2,500

2.9

 Current smoker

39,221

44.7

Maternal alcohol intake, n (%)^b

 Never drank

29,329

33.5

 Ex-drinker who quit before pregnancy

14,835

16.9

 Current drinker

42,837

48.9

Annual household income, n (%)^b

 < 4 million, Yen

32,249

36.79

 4–8 million, Yen

40,648

46.4

 > 8 million, Yen

5,460

6.2

Verbal abuse from a partner, n (%)^b

 No

75,734

86.4

 Yes

11,591

13.2

Physical abuse from a partner, n (%)^b

 No

86,447

98.6

 Yes

988

1.1

Mother-to-Infant Bonding score at 1 year after birth^c

1.95

2.3

Mother-to-Infant Bonding score at 1 year after birth^c

 ≤ 4

78,219

88.5

 ≥ 5

10,205

11.5

Multiple births, n (%)^c

 No

86,832

98.2

 Yes

1,592

1.8

Infant’s sex, n (%)^c

 Male

45,335

51.3

 Female

43,089

48.7