Table 3 Multivariate adjusted association between maternal multimorbidity and preterm birth

Maternal multimorbidity

1.64 (1.48–1.82)

1.69 (1.52–1.89)

1.22 (0.9–1.66)

0.86 (0.51–1.44)

No MM

Ref

Ref

Ref

Ref

Adjusted for maternal age, socioeconomic status, ethnicity, number of previous pregnancies, BMI and smoking history. SIMD: Scottish Index of Multiple Deprivation. BMI: body mass index

Age at conception, years

 15–19

1.13 (0.94–1.36)

1.13 (0.92–1.38)

1 (0.56–1.78)

1.79 (0.87–3.7)

 20–24

1 (0.87–1.14)

0.97 (0.85–1.12)

1.22 (0.84–1.79)

1.37 (0.79–2.38)

 25–29

Ref

Ref

Ref

Ref

 30–34

1.11 (0.99–1.25)

1.06 (0.94–1.2)

1.48 (1.05–2.09)

1.09 (0.64–1.86)

 35–39

1.24 (1.08–1.44)

1.18 (1.01–1.37)

1.49 (0.97–2.27)

1.18 (0.61–2.26)

 40–44

1.72 (1.35–2.21)

1.7 (1.32–2.2)

1.14 (0.48–2.71)

0.73 (0.17–3.21)

 45–49

1.07 (0.33–3.46)

1.03 (0.32–3.31)

ISS

ISS

SIMD

 Most deprived 1

1.31 (1.1–1.55)

1.18 (0.99–1.41)

3.34 (1.73–6.46)

1.11 (0.53–2.34)

 2

1.27 (1.07–1.51)

1.16 (0.97–1.39)

3.28 (1.69–6.35)

1.25 (0.59–2.63)

 3

1.14 (0.95–1.36)

1.06 (0.88–1.28)

2.34 (1.18–4.67)

1.11 (0.51–2.41)

 4

1.11 (0.93–1.32)

1.03 (0.86–1.23)

2.3 (1.16–4.56)

0.97 (0.44–2.14)

 Least deprived 5

Ref

Ref

Ref

Ref

 Missing

1.04 (0.85–1.26)

1 (0.81–1.22)

2.19 (1.06–4.53)

0.61 (0.23–1.62)

Previous pregnancies

 0

Ref

Ref

Ref

Ref

 1

0.76 (0.68–0.85)

0.8 (0.71–0.9)

0.57 (0.4–0.81)

0.67 (0.41–1.12)

 2

0.8 (0.7–0.91)

0.81 (0.7–0.94)

0.68 (0.46–1.02)

0.75 (0.41–1.36)

 3

0.92 (0.79–1.08)

0.9 (0.76–1.07)

1.13 (0.74–1.73)

0.92 (0.45–1.86)

 4

1.03 (0.84–1.25)

1.01 (0.82–1.25)

1.11 (0.65–1.89)

1.05 (0.44–2.49)

 5 + 

1.27 (1.06–1.53)

1.13 (0.93–1.38)

1.41 (0.87–2.29)

1.84 (0.89–3.79)

 Unknown

1.84 (0.23–14.62)

1.59 (0.36–6.99)

ISS

ISS

Ethnicity

 White

1.26 (0.61–2.62)

1.54 (0.67–3.52)

0.64 (0.16–2.62)

0.44 (0.06–3.26)

 Mixed ethnic groups

1.24 (0.3–5.04)

1.75 (0.41–7.47)

ISS

ISS

 Black

Ref

Ref

Ref

Ref

 Asian

1.63 (0.75–3.55)

2 (0.83–4.84)

0.28 (0.04–1.99)

1.26 (0.14–11.01)

 Others

1.47 (0.66–3.24)

1.63 (0.66–4)

0.85 (0.17–4.23)

0.49 (0.04–5.58)

 Missing

1.14 (0.55–2.38)

1.45 (0.63–3.33)

0.47 (0.11–1.96)

0.36 (0.05–2.76)

BMI, kg/m²

 Underweight (< 18.5)

1.36 (1.03–1.81)

1.31 (0.97–1.76)

1.2 (0.51–2.85)

1.52 (0.45–5.09)

 Normal weight (18.5–24.9)

Ref

Ref

Ref

Ref

 Overweight (25–29.9)

0.98 (0.86–1.12)

0.93 (0.81–1.06)

1.26 (0.88–1.81)

2.09 (1.23–3.57)

 Obese(> 30)

1.11 (0.98–1.26)

1.05 (0.92–1.2)

1.34 (0.94–1.93)

1.67 (0.93–2.98)

 Missing

1.31 (1.15–1.49)

1.28 (1.11–1.47)

1.23 (0.84–1.82)

1.52 (0.82–2.81)

Smoking history

 Never smoked

Ref

Ref

Ref

Ref

 Current smoker

1.44 (1.28–1.61)

1.4 (1.24–1.58)

1.67 (1.22–2.29)

2.14 (1.33–3.43)

 Former smoker

0.85 (0.73–0.99)

0.89 (0.75–1.04)

0.93 (0.6–1.45)

0.79 (0.38–1.67)

 Not known

1.4 (1.18–1.65)

1.31 (1.1–1.56)

1.52 (0.95–2.45)

1.94 (0.97–3.89)