Table 1 The influencing factor assignment table

X₁

Pregnant women’s age

1 = 18- 2 = 25- 3 = 35-

X₂

Pregnant women’s degree

1 = Primary school and below 2 = Middle school 3 = College or university

X₃

Number of delivery of pregnant women (including this time)

1 = 1 2 = 2 3 = 3

X₄

Biological sample collection period

1 = Non -heating period 2 = Heating period

X₅

Whether the housing is decorated within one year before childbirth

1 = No 2 = Yes

X₆

The ventilation of the house where the house lives during pregnancy

1 = Very good 2 = Good 3 = Poor

X₇

The distance between the place of residence is from the road

1 = Far away(≥800 m)2 = Closer (400-800 m) 3 = Beside the road (≤400 m)

X₈

Pregnancy heating method

1 = Heating 2 = Stove 3 = Electricity

X₉

Whether there are tapestry in housing during pregnancy

1 = No 2 = Yes

X₁₀

Eat barbecue and fried food during pregnancy

1 = No 2 = Yes

X₁₁

Husband smoke

1 = No 2 = Yes

X₁₂

Gender of Newborn

1 = Male 2 = Female