Table 1 Characteristics of participants with or without placental abnormality.

Participants, n

79,051

467

342

160

Maternal age at delivery, years (mean ± SD)

31.2 ± 5.1

33.5 ± 4.7 ^b

32.0 ± 5.2 ^{b c}

32.3 ± 5.2^b

<0.001^a

   <20 years

674 (0.9)

0 (0.0)

5 (1.5)

0 (0.0)

   20–34 years

56,798 (71.8)

250 (53.5)

216 (63.2)

96 (60.0)

   35 + years

21,579 (27.3)

217 (46.5)

121 (35.4)

64 (40.0)

<0.001

Maternal BMI before pregnancy, kg/m² (mean ± SD)

21.2 ± 3.3

21.3 ± 3.2

21.6 ± 3.7

21.6 ± 3.4

0.10^a

   Underweight (BMI < 18.5), n (%)

12,781 (16.2)

66 (14.1)

57 (16.7)

25 (15.6)

   Normal weight BMI 18.5–24.9), n (%)

57,911 (73.3)

350 (74.9)

239 (69.9)

115 (71.9)

   Overweight (BMI 25.0+), n (%)

8,359 (10.6)

51 (10.9)

46 (13.5)

20 (12.5)

0.51

   Multiparous, n (%)

45,402 (57.4)

276 (59.1)

193 (56.4)

96 (60.0)

0.78

Past history of cesarean section, n (%)

6,968 (8.8)

56 (12.0)

47 (13.7)

8 (5.0)

<0.001

Recurrent pregnancy loss, n (%)

813 (1.0)

11 (2.4)

3 (0.9)

2 (1.3)

0.043

   Spontaneous

73,967 (93.6)

394 (84.4)

310 (90.6)

123 (76.9)

   Ovulation induction through medication

2,112 (2.7)

17 (3.6)

7 (2.0)

3 (1.9)

   Artificial insemination or in-vitro fertilization

2,972 (3.8)

56 (12.0)

25 (7.3)

34 (21.3)

<0.001

Smoking during pregnancy, n (%)

3,572 (4.5)

17 (3.6)

26 (7.6)

14 (8.8)

0.002

Drinking during pregnancy, n (%)

2,012 (2.5)

10 (2.1)

8 (2.3)

13 (8.1)

<0.001

   Infrequent (<3 days per week)

1438 (1.8)

6 (1.3)

4 (1.2)

9 (8.3)

   Frequent (3+ days per week)

574 (0.3)

4 (0.9)

4 (1.2)

4 (2.5)

0.001

   Low (<1.5 drinks per week)

1508 (1.9)

6 (1.3)

4 (1.2)

10 (6.3)

   High (1.5+ drinks per week)

504 (0.6)

4 (0.9)

4 (1.2)

3 (1.9)

0.001