Table 1 The maternal and neonatal characteristics of study participants

From: Twin pregnancies are risk factors for both early- and late-onset hypertensive disorders of pregnancy: the Japan Environment and Children’s study

Variables

All participants (N = 86,717) 1

Singleton pregnancies (N = 86,024) 1

Twin pregnancies

 

DD-twin pregnancies (N = 441) 1

MD-twin pregnancies (N = 252) 1

Maternal age, N (%)

30.8 (5.0)

30.8 (5.0)

31.9 (4.9)

30.4 (4.8)

<25 years

9672 (11.2)

9616 (11,2)

31 (7.0)

25 (9,9)

25–29.9 years

25,449 (29.3)

25,242 (29.3)

115 (26.1)

92 (36.5)

30–34.9 years

30,301 (34.9)

30,064 (34.9)

150 (34.0)

87 (34.5)

35–39.9 years

18,146 (20.9)

17,989 (20.9)

119 (27.0)

38 (15.1)

≥40 years

3145 (3.6)

3109 (3.6)

26 (5.9)

10 (4.0)

Missing

4 (0.0)

4 (0.0)

0 (0.0)

0 (0.0)

Maternal birth weight, N (%)

    

<2500 g

3814 (4.4)

3783 (4.4)

21 (4.8)

10 (4.0)

2500–3999 g

72,370 (83.5)

71,794 (83.5)

366 (83.0)

210 (83.3)

≥4000 g

1780 (2.1)

1765 (2.1)

10 (2.3)

5 (2.0)

Missing

8753 (10.1)

8682 (10.1)

44 (10.0)

27 (10.7)

Maternal height, cm

158.1 (5.3)

158.1 (5.3)

158.8 (5.3)

157.8 (5.3)

Pre-pregnancy BMI kg/m2, N (%)

21.1 (3.1)

21.1 (3.1)

21.4 (3.4)

21.0 (3.4)

Underweight (<18.5 kg/m2)

14,225 (16.4)

14,104 (16.4)

71 (16.1)

50 (19.8)

Normal range (18.5–24.9 kg/m2)

63,907 (73.7)

63,408 (73.7)

321 (72.8)

178 (70.6)

Overweight/Obesity (≥25.0 kg/m2)

8551 (9.9)

8478 (9.9)

49 (11.1)

24 (9.5)

Missing

34 (0.0)

34 (0.0)

0 (0.0)

0 (0.0)

Parity, N (%)

    

Primipara

48,528 (56.0)

48,199 (56.0)

206 (46.7)

123 (48.8)

Multipara

36,089 (41.6)

35,735 (41.5)

226 (51.2)

128 (50.8)

Missing

2100 (2.4)

2090 (2.4)

9 (2.0)

1 (0.4)

Conception method, N (%)

    

Spontaneous pregnancy

80,430 (92.7)

79,970 (93.0)

237 (53.7)

223 (88.5)

Non-ART

3284 (3.8)

3145 (3.7)

133 (30.2)

6 (2.4)

ART

2636 (3.0)

2544 (3.0)

71 (16.1)

21 (8.3)

Missing

367 (0.4)

365 (0.4)

0 (0.0)

2 (0.8)

MAP level during early gestation, N (%)

79.1 (9.0)

79.1 (9.0)

81.1 (8.9)

81.7 (9.0)

SLE and/or APS

200 (0.2)

198 (0.2)

1 (0.2)

1 (0.4)

The history of kidney disease, N (%)

364 (0.4)

360 (0.4)

3 (0.7)

1 (0.4)

The history of mental disorders, N (%)

6771 (7.8)

6731 (7.8)

26 (5.9)

14 (5.6)

Type 1 diabetes mellitus

60 (0.1)

60 (0.1)

0 (0.0)

0 (0.0)

Type 2 diabetes mellitus

97 (0.1)

96 (0.1)

1 (0.2)

0 (0.0)

Smoking status, N (%)

    

Never

50,467 (58.2)

50,053 (58.2)

260 (59.0)

154 (61.1)

Previously did, but quit before realizing current pregnancy

20,039 (23.1)

19,878 (23.1)

108 (24.5)

53 (21.0)

Previously did, but quit after realizing current pregnancy

11,575 (13.3)

11,477 (13.3)

62 (14.1)

36 (14.3)

Currently smoking

4005 (4.6)

3985 (4.6)

11 (2.5)

9 (3.6)

Missing

631 (0.7)

631 (0.7)

0 (0.0)

0 (0.0)

Alcohol drinking status, N (%)

    

Never

29,698 (34.2)

29,477 (34.3)

146 (33.1)

75 (29.8)

Quit drinking before

47,874 (55.2)

47,469 (55.2)

246 (55.8)

159 (63.1)

Continued drinking

8756 (10.1)

8689 (10.1)

49 (11.1)

18 (7.1)

Missing

389 (0.4)

389 (0.5)

0 (0.0)

0 (0.0)

Highest maternal education level, N (%)

    

<13 years

30,446 (35.1)

30,230 (35.1)

137 (31.1)

79 (31.3)

≥13 years

55,130 (63.6)

54,667 (63.5)

295 (66.9)

168 (66.7)

Missing

1141 (1.3)

1127 (1.3)

9 (2.0)

5 (2.0)

Annual household income (million, Japanese Yen), N (%)

    

<4

31,841 (36.7)

31,603 (36.7)

145 (32.9)

93 (36.9)

≥4

39,374 (45.4)

39,068 (45.4)

196 (44.4)

110 (43.7)

Missing

15,502 (17.9)

15,353 (17.8)

100 (22.7)

49 (19.4)

Marital status, N (%)

    

Married

82,439 (95.1)

81,772 (95.1)

431 (97.7)

236 (93.7)

Unmarried

3148 (3.6)

3133 (3.6)

6 (1.4)

9 (3.6)

Divorced or widowed

746 (0.9)

738 (0.9)

3 (0.7)

5 (2.0)

Missing

384 (0.4)

381 (0.4)

1 (0.2)

2 (0.8)

New-onset HDP, N (%)

    

Early-onset HDP

445 (0.5)

423 (0.5)

12 (2.7)

10 (4.0)

Late-onset HDP

1669 (1.9)

1637 (1.9)

18 (4.1)

14 (5.6)

GDM, N (%)

2268 (2.6)

2239 (2.6)

15 (3.4)

14 (5.6)

Gestational weeks at delivery, weeks

39.2 (1.6)

39.3 (1.5)

36.5 (2.0)

35.9 (2.4)

Regions where

    

Regional Centres exist, N (%)

    

Hokkaido

6852 (7.9)

6824 (7.9)

10 (2.3)

18 (7.1)

Tohoku

19,097 (22.0)

18,930 (22.0)

103 (23.4)

64 (25.4)

Kanto

10,266 (11.8)

10,219 (11.9)

35 (7.9)

12 (4.8)

Chubu

15,668 (18.1)

15,545 (18.1)

80 (18.1)

43 (17.1)

Kinki

14,695 (16.9)

14,538 (16.9)

104 (23.6)

53 (21.0)

Chugoku

2622 (3.0)

2593 (3.0)

21 (4.8)

8 (3.2)

Shikoku

5975 (6.9)

5934 (6.9)

23 (5.2)

18 (7.1)

Kyushu-Okinawa

11,542 (13.3)

11,441 (13.3)

65 (14.7)

36 (14.3)

  1. 1Continuous variables are expressed as mean (SD). Categorical variables are expressed as N (%)
  2. APS antiphospholipid antibody syndrome, ART assisted reproductive technology, BMI body mass index, DD dichorionic diamniotic, GDM gestational diabetes mellitus, HDP hypertensive disorders of pregnancy, MAP mean arterial pressure, MD monochorionic diamniotic, SD standard deviation, SLE systemic lupus erythematosus
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