Table 3 Preterm birth logistic regression GAM (model 2.1)

Heatwave (ref: 0)

1

0.85

0.82

0.87

0.09

<0.0001

Great Recession (continuous)

1.04

0.97

1.13

0.02

0.27

COVID (continuous)

0.98

0.92

1.03

0.01

0.40

Time (by month)

1.00

1.00

1.00

0.00

<0.0001

SSEP (/10 points)

0.96

0.95

0.97

0.02

<0.0001

Altitude (/100m)

1.00

1.00

1.00

0.00

1.00

Parity (ref: 1)

2

0.67

0.66

0.69

0.22

<0.0001

3

0.68

0.67

0.70

0.21

<0.0001

>3

0.78

0.74

0.81

0.14

<0.0001

Sex (ref: male)

Female

0.84

0.83

0.85

0.10

<0.0001

Urban (ref: rural)

Urban

0.95

0.94

0.97

0.03

<0.0001

Language region (ref: German)

French

1.05

1.03

1.07

0.03

<0.0001

Italian

1.00

0.96

1.05

0.00

0.87

Maternal nationality (ref: Swiss)

Africa

1.01

0.96

1.05

0.00

0.83

Asia

1.07

1.03

1.12

0.04

<0.01

Europe

0.95

0.93

0.97

0.03

<0.0001

Northern America

0.85

0.76

0.94

0.09

<0.01

Southern/Central America

1.09

1.03

1.15

0.05

<0.01

Civil status (ref: married)

Single

1.12

1.10

1.14

0.06

<0.0001

Smooth variables

 Maternal age (years)

<0.0001

 Seasonality (month)

<0.0001

n=1’263’853