Table 1 Maternal medical background and obstetric outcomes

Maternal medical background

 VitD intake before pregnancy, μg/day, median (IQR)

1.4 (0.8–1.8)

3.0 (2.6–3.3)

4.3 (4.0–4.7)

6.0 (5.5–6.7)

10.2 (8.6–12.8)

 < 0.001^a

 Maternal age, years, mean (SD)

30.0 (5.3)

31.0 (5.0)

31.4 (4.9)

31.8 (4.8)

31.8 (4.9)

 < 0.001^b

Advanced maternal age, %

  < 20

1.6

0.7

0.5

0.5

0.6

 < 0.001^c

 20–29

45.7

37.7

35.1

31.6

31.8

 30–39

49.1

57.4

59.6

62.8

62.3

  > 40

3.6

4.1

4.8

5.2

5.3

BMI before pregnancy (kg/m²), %

  < 18.5

17.2

16.6

15.8

15.7

15.1

 < 0.001^c

 18.5–25.0

71.7

73.1

74.0

73.9

73.1

  > 25.0

11.1

10.3

10.2

10.4

11.8

Smoking during pregnancy, %

6.6

4.7

4.3

3.9

4.6

 < 0.001^c

Primipara, %

51.3

42.5

39.2

35.8

32.7

 < 0.001^c

ART pregnancy, %

2.2

3.0

3.3

3.2

2.9

 < 0.001^c

Chronic Hypertension, %

1.3

1.1

1.1

1.2

1.3

0.240

Glucose intolerance, %

1.6

1.7

1.8

1.6

2.1

0.002

Endometriosis, %

3.0

3.6

3.8

3.8

3.9

 < 0.001^c

Maternal education, years, %

  < 10

7.1

4.6

4.1

3.8

4.5

 < 0.001^c

 10–12

38.6

32.9

29.6

27.5

29.1

 13–16

38.7

41.8

43.1

42.9

44.2

  > 17

15.7

20.8

23.2

25.8

22.2

Annual household income, %

  < 2,000,000 JPY

8.7

5.4

4.5

4.2

5.6

 < 0.001^c

 2,000,000–5,999,999 JPY

69.6

68.7

67.7

66.1

66.0

 6,000,000–9,999,999 JPY

18.5

21.9

23.4

24.7

23.7

  > 10,000,000 JPY

3.3

3.9

4.5

4.9

4.7

Daily calorie intake, kcal/day, median (IQR)

1307 (1049–1939)

1523 (1282–1813)

1657 (1416–1952)

1881 (1594–2637)

2254 (1850–3578)

 < 0.001^a

Obstetric outcomes

 PTB at < 37 weeks, %

4.5

4.8

4.5

4.4

4.8

0.768^d

 PTB at < 34 weeks, %

0.9

1.0

0.9

0.8

1.0

0.676^d

 LBW < 2500 g, %

8.2

8.3

7.8

7.5

8.2

0.175^d

 LBW < 1500 g, %

0.6

0.6

0.5

0.5

0.6

0.443^d

 SGA, %

5.1

5.0

4.6

5.0

5.6

0.031^d

 HDP, %

3.3

3.1

2.9

3.1

3.1

0.360^d