Table 1 Baseline information

2.1.1 Demographic characteristics of pregnant women

Age

Ethnic group

  < 35

4898

(85.6)

Han

5423

(94.7)

  ≥ 35

827

(14.4)

Minority

302

(5.3)

Pre-BMI

  < 18.5(Underweight)

928

(16.2)

  18.5 ~ 23.9(Normal weight)

3946

(68.9)

highest education level

  24 ~ 28(Overweight)

647

(11.3)

Postgraduate and above

470

(8.2)

  > 28(Obesity)

204

(3.6)

College/university degree

4059

(70.9)

Per capita monthly household income (RMB)

High school/equivalent high school diploma and below

1196

(20.9)

  < 1000

22

(0.4)

  1000 ~  < 3000

218

(3.8)

  3000 ~  < 5000

1295

(22.6)

  5000 ~  < 10,000

2323

(40.6)

  10,000 ~  < 30,000

1629

(28.4)

  ≥ 30,000

238

(4.2)

2.1.2 History of allergies of pregnant women and family members

Pregnant women

Pre-existing allergies

Classification of allergy history

  Yes

1383

(24.2)

One

1304

(22.8)

  No

4342

(75.8)

Two

288

(5.0)

More than three

87

(1.5)

None

4045

(70.7)

Fathers

Mothers

Pre-existing allergies

Pre-existing allergies

  Yes

343

(6.0)

Yes

390

(6.8)

  No

5382

(94.0)

No

5335

(93.2)

Classification of allergy history

Classification of allergy history

  One

319

(93.0)

One

352

(90.3)

  Two

22

(6.4)

Two

29

(7.4)

  More than three

2

(0.6)

More than three

9

(2.3)

2.1.3 Exposure in living or working environment of pregnant women

Exposure to allergens when working

Planting

  Yes

167

(2.9)

Yes

3288

(57.4)

  No

5558

(97.1)

No

2437

(42.6)

Decorations

Pets contacting

  < Half a year

95

(1.7)

Never

4852

(84.7)

  Half a year ~  < Two years

1191

(20.8)

Occasional contact (1–2

521

(9.1)

  ≥ Two years

4439

(77.5)

times/month)

Frequent contact (not close)

255

(4.5)

Carpet

Close contact (daily contact)

97

(1.7)

  Yes

575

(10.0)

  No

5150

(90.0)

Plush toys

Main cooking fuel

Yes

1104

(19.3)

  Fuel gas

2061

(36.0)

No

4621

(80.7)

  Electricity

3538

(61.8)

Disinfectants

  Coal

126

(2.2)

Yes

601

(10.5)

Ventilation system

No

5124

(89.5)

  Natural ventilation

545

(9.5)

Mosquito repellents

  Fans

299

(5.2)

Yes

330

(5.8)

  Air-conditions

4881

(85.3)

No

5395

(94.2)

Heating facilities

Insecticides

  Heating radiator

806

(14.1)

Yes

45

(0.8)

  Air-conditioner

3556

(62.1)

No

5680

(99.2)

  Stove

1363

(23.8)

Air fresheners

Home humidity

Yes

175

(3.1)

  Moist

70

(1.2)

No

5550

(96.9)

  Moderate

4634

(81.0)

  Dry

1021

(17.8)

2.1.4. Smoking and alcohol use among pregnant women

Smoking

Drinking frequency

  Active smoking

28

(3.0)

Everyday

2

(0.7)

  Passive smoking

908

(97.0)

Every week

12

(4.3)

  Total

936

(100.0)

Every month

268

(95.0)

Total

282

(100.0)

2.1.5 Medication and probiotics intake among pregnant women

Medication intake

Progesterone-type tocolytic

  Yes

2525

(44.1)

agents

  No

3200

(55.9)

Yes

2320

(2.7)

Antihistamines

No

3405

(97.3)

  Yes

44

(0.8)

Single or combined medication

  No

5681

(99.2)

Only one

2268

(89.8)

Antibiotics for 3 consecutive days

Two at once

216

(8.6)

  Yes

233

(4.1)

Three or more at once

41

(1.6)

  No

5492

(95.9)

Probiotics

Glucocorticoids

Everyday

40

(5.2)

  Yes

76

(1.3)

 ≥ 3 days every week

261

(34.1)

  No

5649

(98.7)

 ≤ 2 days every week

98

(12.8)

Antipyretic analgesics

1 ~ 3 days every month

366

(47.9)

  Yes

153

(2.5)

Total

765

(100.0)

  No

5572

(97.5)