Table 1 Characteristics of the participants (n = 71,878 mother–toddler pairs)

Toddler

Infant sex

 Male

29,855

(51.0)

6,809

(51.0)

0.994

 Female

28,675

(49.0)

6,539

(49.0)

Any major congenital anomaly

 No

57,394

(98.1)

12,892

(96.6)

< 0.001

 Yes

1,136

(1.9)

456

(3.4)

Gestational age, wk

 ≥41

5,786

(9.9)

1,012

(7.6)

< 0.001

 37–40

50,898

(87.0)

10,914

(81.8)

 34–36

1,654

(2.8)

965

(7.2)

 <34

192

(0.3)

457

(3.4)

Started solid food at 6 months

 No

42,934

(73.4)

9,367

(70.2)

< 0.001

 Yes

14,669

(25.1)

3,744

(28.1)

 Missing

927

(1.6)

237

(1.8)

Breastfeeding

 Already weaned or formula-fed

21,989

(37.6)

5,701

(42.7)

< 0.001

 Yes at least till 1 year

25,749

(44.0)

5,156

(38.6)

 Yes at least till 2 years

9,546

(16.3)

2,226

(16.7)

 Missing

1,246

(2.1)

265

(2.0)

Attendance at a childcare facility (daycare center/nursery) at 1 year

 No

42,262

(72.2)

9,661

(72.4)

0.541

 Yes

14,763

(25.2)

3,366

(25.2)

 Missing

1,505

(2.6)

321

(2.4)

Attendance at a preschool or childcare facility (daycare center/nursery) at 3 years

 No

21,218

(36.3)

4,658

(34.9)

0.012

 Yes

35,579

(60.8)

8,278

(62.0)

 Missing

1,733

(3.0)

412

(3.1)

Constipation at 1 year

 No

56,204

(96.0)

12,855

(96.3)

0.321

 Yes

776

(1.3)

164

(1.2)

 Missing

1,550

(2.7)

329

(2.5)

 Mother

Age during pregnancy, y

 <25

5,705

(9.8)

802

(6.0)

< 0.001

 25 to <30

17,245

(29.5)

2,842

(21.3)

 30 to <35

20,950

(35.8)

4,635

(34.7)

 ≥35

14,286

(24.4)

4,960

(37.2)

Missing

344

(0.6)

109

(0.8)

 Pre-pregnancy body mass index, kg/m²

 <18.5

9,947

(17.0)

1,719

(12.9)

< 0.001

 18.5 to <25

43,514

(74.3)

9,523

(71.3)

 ≥25

5,036

(8.6)

2,096

(15.7)

 Missing

33

(0.1)

10

(0.1)

Parity

 Primipara

25,128

(42.9)

5,759

(43.2)

0.902

 Multipara

31,904

(54.5)

7,250

(54.3)

 Missing

1,498

(2.6)

339

(2.5)

Maternal history of allergy

 No

29,208

(49.9)

6,663

(49.9)

0.993

 Yes

28,989

(49.5)

6,608

(49.5)

 Missing

333

(0.6)

77

(0.6)

Use of antibacterial drug during pregnancy

 No

52,370

(89.5)

11,906

(89.2)

0.345

 Yes

6,160

(10.5)

1,442

(10.8)

Annual household income, million Japanese yen

 <4

21,211

(36.2)

4,783

(35.8)

0.047

 4 to <6

18,282

(31.2)

4,098

(30.7)

 ≥6

14,882

(25.4)

3,549

(26.6)

Missing

4,155

(7.1)

918

(6.9)

 Highest education level, y

 ≤12

19,602

(33.5)

4,600

(34.5)

< 0.001

 >12 to <16

24,733

(42.3)

5,737

(43.0)

 ≥16

13,578

(23.2)

2,836

(21.3)

 Missing

617

(1.1)

175

(1.3)

Employed during pregnancy

 No

26,177

(44.7)

5,982

(44.8)

0.025

 Yes

31,553

(53.9)

7,143

(53.5)

 Missing

800

(1.4)

223

(1.7)

Marital status

 Married

55,577

(95.0)

12,728

(95.4)

< 0.001

 Single

2,004

(3.4)

383

(2.9)

 Divorced or widowed

386

(0.7)

118

(0.9)

 Missing

563

(1.0)

119

(0.9)

Physical activity

 No

13,625

(23.3)

3,404

(25.5)

< 0.001

 Yes

44,424

(75.9)

9,802

(73.4)

 Missing

481

(0.8)

142

(1.1)

Quintile of energy intake, cal

 Q1 (≤1,228)

11,389

(19.5)

2,566

(19.2)

0.001

 Q2 ( 1,229–1,490)

11,934

(20.4)

2,583

(19.4)

 Q3 ( 1,491–1,750)

11,807

(20.2)

2,697

(20.2)

 Q4 ( 1,751–2,127)

11,687

(20.0)

2,680

(20.1)

 Q5 (≥2,128)

11,368

(19.4)

2,712

(20.3)

 Missing

345

(0.6)

110

(0.8)

Smoking status at 1 month

 Never smoked

35,428

(60.5)

7,755

(58.1)

< 0.001

 Previously smoked but quit before finding out about the current pregnancy

12,936

(22.1)

3,126

(23.4)

 Previously smoked but quit after finding out about the current pregnancy

7,795

(13.3)

1,815

(13.6)

 Still smokes (1–10 per day)

1,558

(2.7)

394

(3.0)

 Still smokes (≥11 per day)

368

(0.6)

95

(0.7)

 Missing

445

(0.8)

163

(1.2)

Passive smoking status at 1 month

 No one smoked

28,634

(48.9)

6,564

(49.2)

< 0.001

 Someone smoked but not in the presence of the baby

28,212

(48.2)

6,308

(47.3)

 Someone smoked in the presence of the baby

1,295

(2.2)

298

(2.2)

 Missing

389

(0.7)

178

(1.3)

Alcohol consumption at 1 month

 Never drank

53,390

(91.2)

12,045

(90.2)

< 0.001

 Drank in the past but stopped drinking

2,535

(4.3)

603

(4.5)

 Still drinks

2,205

(3.8)

538

(4.0)

 Missing

400

(0.7)

162

(1.2)