Table 1 Characteristics of eligible studies included in this meta-analysis of parity and bladder cancer risk

Cantor et al. 1992 [20]

Case-control study

USA, 1986–1989

5

40–85

315; 821

1

Reference

Not reported

2

1.4 (0.8–2.4)

3

1.6 (0.9–2.9)

4

0.9 (0.5–1.8)

5+

1.5 (0.8–2.7)

La Vecchia et al. 1993 [21]

Case-control study

Italy, 1983–1992

6

Case: blow 70; Control: 58 (median)

68; 5619

0

Reference

Age, education, parity, number of abortions, oral contraceptive and other female hormone use

1

1.2

2

1.0

3

0.8

≥4

0.7

Pelucchi et al. 2002 [10]

Case-control study

Italy, 1985–1992

6

Case: 30–79 Control: 26–79

110; 289

0–1

Reference

Age, study center, education, BMI, cigarette smoking, and coffee and alcohol consumption

2–3

0.83 (0.47–1.45)

≥4

0.88(0.41–1.90)

Cantwell et al. 2006 [8]

Cohort study

USA, 1980–1998

7

Case: 55.4 ± 8.8 Participants: 70.6 ± 8.4,

167; 54308

0

Reference

Age, calendar year and smoking status (never, former or current).

1

0.65 (0.36–1.18)

2

0.96 (0,61–1,。50)

3

0.82 (0.5–1.34)

>4

0.75 (0.45–1.25)

McGrath et al. 2006 [11]

Cohort study, US Nurses’ Health Study

USA, 1976–2002

7

30–55

336; 116598

0

Reference

Age (months), time period (2-year questionnaire period), smoking status (never, former, current) and pack-years of smoking (continuous), and body mass index

1–2

0.85 (0.56–1.28)

3–4

0.70 (0.47–1.05)

≥4

0.84 (0.54–1.32)

Prizment et al. 2006 [22]

Cohort study, The Iowa Women’s Health Study

USA, 1986–2003

7

55–69

192; 37459

0

Reference

Age, smoking status and pack-years

1–2

0.81 (0.50–1.32)

3–4

0.79 (0.48–1.27)

≥5

0.79 (0.46–1.37)

Huang et al. 2009 [7]

Case-control study

Spanish, 1998–2001

6

Median: case 67.4

152; 166

0

Reference

Age, smoking status, and high-risk occupation

Control:67.8

≥1

0.43 (0.2–0.9)

Davis-Dao et al. 2011 [13]

USA and China,

6

LAS:25–64;

LAS:349/349

LA:1

LA: Reference

LASBCS: smoking status in the reference year (current, former, never), pack-years of smoking, and BMI; CTS: race/ethnicity, smoking status and BMI.

Los Angeles Bladder Cancer Study (LAS): Case-control study;

Los Angeles: 1987–1996;

SHS:25–74;

SHS: 131/138

2

0.41 (0.98–0.87)

CTS: not reported

CTS: 196/120857

3

0.63 (0.29–1.34)

≥4

0.70 (0.35–1.39)

Shanghai Bladder Cancer Study (SHS): Case-control study

Shanghai:1995–1998;

SH: 1

SH: reference

2

0.63 (0.23–1.74)

3

0.47 (0.16–1.33)

California Teachers Study(CTS): Cohort study

CTS:1995–2005

≥4

0.56 (0.21–1.48)

CTS:1

CTS: reference

2

1.14 (0.71–1.86)

3

0.73 (0.42–1.27)

≥4

1.06 (0.61–1.87)

Dietrich et al. 2011 [12]

Case-control study

USA, 1994–2001; 1993

6

25–74

207/403

0

Reference

Age and smoking status

July; 1995–1997

1–2

0.67 (0.36–1.24)

3–4

0.75 (0.40–1.39)

≥5

0.74 (0.35–1.57)

Daugherty et al. 2013 [23]

Cohort study, NIH-AARP Diet and Health Study

USA, 1995–2006

7

50–71

651/201492

0

Reference

Age

1

0.78 (0.58–1.07)

2

0.72 (0.56–0.92)

3–4

0.78 (0.62–0.98)

5+

0.73 (0.54–0.98)

Kabat et al. 2013 [24]

Cohort study, Women’s Health Initiative

USA, 1993–1998

6

50–79

480/145048

0

Reference

Age, education, pack-years, alcohol intake, parity, oral contraceptive use (ever, never)

1–2

0.71 (0.53–0.96)

3–4

0.84 (0.63–1.12)

≥5

0.72 (0.51–1.03)

Weibull et al. 2013 [6]

Cohort study

Sweden, 1964–2009, Median follow-up time:16.6 years

7

40~

2860/2009811

1

Reference

Age, highest educational level, and chronic obstructive lung disease.

2

0.85 (0.77–0.95)

≥3

0.76 (0.68–0.86)