Table 1 Characteristics of studies evaluating parity with endometrial cancer risk.

14,069/35,312 (mean from 54.6–71.6y)

Nulliparous

1.0 (ref.)

unadjusted

parous

0.73 (0.71–0.76)

1

0.88 (0.84–0.92)

2

0.78 (0.75–0.81)

3

0.68 (0.65–0.70)

≥4

0.60 (0.57–0.64)

(questionnaire or interview/cancer registry, pathology report, medical chart or slide review)

1,017/302,618 (mean 50.5y), mean 8.7y

Nulliparous

1.0 (ref.)

Age, study center, body mass index (BMI), physical activity, alcohol, diabetes, smoking status and education

Parous

0.65 (0.54–0.77)

Parity = 1

1.0 (ref.)

2

0.92 (0.76–1.11)

3

0.80 (0.64–0.99)

≥4

0.58 (0.44–0.78)

(Self-questionnaire/Cancer registry, histology confirmation)

206/267,400 (N/A), mean 7.6y

Nulliparous

3.95 (1.43–10.86)

Age at baseline

1

1.00 (ref.)

2

0.77 (0.42–1.42)

3

1.07 (0.57–2.04)

4

0.93 (0.46–1.86)

≥5

0.75 (0.36–1.56)

(Trained interviewer/Cancer registry and medical record )

419/86,978 (N/A), mean 19.3y

Parity number

Age at first birth, birth intensity

5

1.0 (ref.)

6

0.72 (0.57–0.92)

7

0.87 (0.62–1.22)

≥8

0.71 (0.57–1.02)

(Registry/Cancer registry)

physical activity, fruit and vegetable consumption, diabetes, social-economic status, cigarette smoking, alcohol consumption

133/11,659 (median56.2y), mean 20.4y

Nulliparous

1.0 (ref.)

parous

0.83 (0.55–1.25)

1–2

0.9 (0.6–1.5)

≥3

0.4 (0.2–0.8)

(Self-questionnaire/Cancer registry)

554/765,756 (30–56y), mean 12.2y

Nulliparous

1.94 (1.46–2.59)

Age, birth cohort

1

1.00

2

0.84 (0.64–1.09)

3

0.61 (0.46–0.82)

≥4

0.48 (0.34–0.69)

(Registry/cancer registry)

420/62,079 (27–69y), 19y

Nulliparous

1.0 (ref.)

Age, urban/rural place of residence

parous

0.66 (0.53–0.84)

1

0.80 (0.59–1.10)

2

0.72 (0.55–0.96)

3

0.55 (0.39–0.77)

4

0.72 (0.50–1.06)

≥5

0.41 (0.26–0.66)

(Trained interviewer/Cancer registry)

417/40562 (mean 62.8y), ~13y

Nulliparous

1.0 (ref.)

birth year and entry year, age at last menstrual period, age at menarche, BMI, oral contraceptive use, menopausal hormone therapy use, diabetes and smoking status

parous

0.76 (0.57–1.01)

(questionnaire/cancer registry and questionnaire)

125/10050 (mean ~57y), ~15y

Nulliparous

1.0 (ref.)

birth year and entry year, age at last menstrual period, age at menarche, BMI, oral contraceptive use, menopausal hormone therapy use, diabetes and smoking status

parous

0.60 (0.40–0.88)

(questionnaire/database link and questionnaire)

147/1047 (40–65y), up to 18 y

Nulliparous

1.0 (ref.)

unadjusted

Parous

0.61 (0.45–0.84)

1–2

0.74 (0.52–1.04)

≥3

0.49 (0.33–0.72)

(questionnaire/database link)

31118/5759120 (NA), up to 45 y

Nulliparous

1.0 (ref.)

age, period, region, socioeconomic status

1

0.47 (0.42–0.52)

2

0.41 (0.37–0.46)

3–4

0.36 (0.32–0.40)

5–9

0.29 (0.25–0.34)

10+

0.25 (0.10–0.58)

(database/database link)

Cases/control (age)

Parity categories (exposure/case assessment)

RR (95% CI)

Matched/Adjusted factors

237/538 (25℃49y)

Nulliparous

1.0 (ref.)

Age, residence, family history of endometrial cancer, BMI, diabetes mellitus, hypertension, menarche, pregnancy, number of pregnancy, number of induced abortions, age of first birth, hyperandrogenism, amenorrhea, oral contraceptive use, hormone replacement therapy, cigarette smoking and years of schooling

parous

0.62 (0.50–0.77)

1

0.6 (0.3–1.1)

2

0.3 (0.2–0.6)

≥3

0.2 (0.1–0.4)

(Self-questionnaire/histology confirmation)

85/668 (54.9y)

Nulliparous

1.0 (ref.)

Age, hormonal use, breastfeeding, smoking, diabetes mellitus, hypertension, physical activity, menopausal status, BMI

parous

0.25 (0.12–0.49)

1–2

0.41 (0.19–0.86)

3–4

0.15 (0.06–0.36)

≥5

0.16 (0.06–0.40)

(Trained interviewer/biopsy confirmation)

752/2,606 (25–74y)

Nulliparous

1.0 (ref.)

Age, calendar year at interview, education, BMI, menopausal status, use of hormonal replacement therapy, smoking, history of diabetes, hypertension, abortions, age at first birth, time since last birth

parous

0.91 (0.78–1.06)

1

0.9 (0.7–1.1)

2

0.8 (0.6–1.0)

≥3

0.7 (0.5–0.8)

(Trained interviewer/histology confirmation)

145/298 (NA)

Nulliparous

1.0 (ref.)

Age, schooling, occupation, age at menopause, age at menarche, oral contraceptive, menopausal estrogen, smoking, alcohol intake, coffee intake, BMI, energy intake

parous

0.71 (0.53–0.96)

1

0.75 (0.27–2.11)

2

0.66 (0.26–1.67)

3

0.36 (0.13–1.03)

≥4

0.34 (0.11–1.05)

(Trained interviewer/histologic confirmation)

268/268 (18–74y)

Nulliparous

1.0 (ref.)

Age

parous

0.58 (0.48–0.69)

1

0.3 (0.1–0.8)

2–3

0.2 (0.1–0.7)

≥4

0.1 (0.1–0.4)

(Trained interviewer/Cancer registry)

83/164 (40–79y)

Nulliparous

1.0 (ref.)

unadjusted

parous

1.04 (0.65–1.66)

1–2

1.19 (0.73–1.94)

≥3

0.81 (0.47–1.43)

(Trained interviewer/Biopsy-confirmation)

167/903 (45–74y)

Nulliparous

1.0 (ref.)

Race, education, age at menopause, weight, history of diabetes, oral contraceptive use, age, menopausal status, estrogen replacement therapy use

1

0.8 (0.7–0.9)

(Trained interviewer/pathology confirmation)

476/2128 (40–89y)

Nulliparous

1.0 (ref.)

unadjusted

parous

0.75 (0.63–0.91)

1–2

0.85 (0.69–1.05)

3–4

0.68 (0.54–0.86)

≥5

0.70 (0.55–0.90)

(interview/clinic diagnosis)

437/3200 (20–54y)

Nulliparous

1.0 (ref.)

Location, age, time interval

parous

0.54 (0.45–0.66)

1–2

0.59 (0.48–0.74)

3–4

0.54 (0.43–0.68)

≥5

0.41 (0.29–0.59)

(interview/histological confirmation)

147/1409 (31–65y)

Nulliparous

1.0 (ref.)

unadjusted

parous

0.43 (0.31–0.60)

(interview and/or questioinnaire/hospital records)

197/233 (NA)

Nulliparous

1.0 (ref.)

unadjusted

parous

0.81 (0.66–0.995)

(hospital records/pathology diagnosis)

212/1198 (40–89y)

Nulliparous

1.0 (ref.)

age

parous

0.57 (0.45–0.73)

1

0.74 (0.49–1.13)

2

0.61 (0.44–0.86)

3

0.51 (0.33–0.76)

4+

0.48 (0.33–0.70)

(Questionnaire/histological confirmation)

300/300 (NA)

Nulliparous

1.0 (ref.)

age

parous

0.74 (0.63–0.86)

(records/histological confirmation)

50/50 (30–80y)

Nulliparous

1.0 (ref.)

unadjusted

Parous

0.63 (0.44–0.92)

1–3

0.56 (0.37–0.85)

4+

0.95 (0.59–1.51)

(unclear/clinic diagnosis)

110/110 (45y−)

Nulliparous

1.0 (ref.)

age

Parous

0.61 (0.48–0.78)

1

0.91 (0.66–1.24)

2

0.70 (0.52–0.95)

3

0.51 (0.34–0.79)

4+

0.33 (0.18–0.60)

(trained interviewer/microscopical confirmation)

145/26751 (20y+)

Nulliparous

1.0 (ref.)

Age, first-visit year

Parous

0.83 (0.56–1.25)

1

0.63 (0.35–1.14)

2

0.62 (0.40–0.96)

3+

0.41 (0.25–0.69)

(questionnaire/histology diagnosis)

222/2162 (mean 56y)

Nulliparous

1.0 (ref.)

Age, menstrual-status

Parous

0.51 (0.39–0.68)

1–2

0.56 (0.42–0.74)

≥3

0.40 (0.27–0.60)

(questionnaire/histological confirmation)

7261/19490 (50–80y)

Nulliparous

1.0 (ref.)

age

Parous

0.84 (0.80–0.88)

1–2

0.90 (0.85–0.94)

≥3

0.76 (0.72–0.80)

(registry/cancer registry)

152/285 (mean ~54y)

Nulliparous

1.0 (ref.)

Age, area of residence

Parous

0.63 (0.44–0.89)

1–3

0.94 (0.65–1.36)

≥4

0.89 (0.55–1.44)

(questionnaire/histopathological confirmation)

84/168 (40–69y)

Nulliparous

1.0 (ref.)

Age, county of residence, weight, time since last medical visit, education, diabetes, estrogen pill use

Parous

0.80 (0.68–0.95)

(Trained interviewer/medical record review)

483/693 (30–69y)

Nulliparous

1.0 (ref.)

Age, race, religion, BMI, diabetes history, hypertension history, alcohol use, tobacco use, durations of oral contraceptive and non-contraceptive estrogen use, menopausal status, age at menopause, age at first pregnancy, years of education, date of interview, geographic region

Parous

0.98 (0.84–1.15)

1–2

1.3 (0.9–1.9)

3–4

1.0 (0.7–1.5)

≥5

0.5 (0.3–0.9)

(Trained interviewer/clinic diagnosis)

122/309 (75y−)

Nulliparous

1.0 (ref.)

unadjusted

Parous

0.84 (0.61–1.16)

(Trained interviewer/histological confirmation)

679/944 (45–74y)

Nulliparous

1.0 (ref.)

Age, location

Parous

0.74 (0.64–0.85)

1

0.91 (0.75–1.11)

>1

0.71 (0.62–0.82)

(Trained interviewer//histological confirmation)

145/580 (unknown)

Nulliparous

1.0 (ref.)

age

Parous

0.56 (0.38–0.83)

(Medical record linkage/pathology confirmation)

740/2372 (40–79y)

Nulliparous

1.0 (ref.)

age

Parous

0.68 (0.58–0.80)

1–2

0.8 (0.6–1.0)

3–4

0.6 (0.5–0.8)

≥5

0.4 (0.3–0.6)

(Trained interviewer/registry link and histologic confirmation)

254/254 (30–94y)

Nulliparous

1.0 (ref.)

Age, county of residence

Parous

0.6 (0.4–0.9)

1

0.7 (0.4–1.2)

2

0.7 (0.4–1.1)

3

0.6 (0.3–1.1)

4

0.4 (0.2–0.8)

≥5

0.3 (0.1–0.6)

(Trained interviewer/histologic confirmation)

88/177 (40–74y)

Nulliparous

1.0 (ref.)

age

Parous

1.10 (0.65–1.86)

(Trained interviewer/pathology confirmation)

112/200 (unknown)

Nulliparous

1.0 (ref.)

unadjusted

Parous

0.85 (0.63–1.16)

1

1.09 (0.73–1.64)

2

0.65 (0.42–1.01)

3

0.86 (0.53–1.38)

4

0.96 (0.53–1.73)

5

1.51 (0.71–3.20)

6

1.88 (1.02–3.48)

7

0.31 (0.05–1.99)

(Trained interviewer/histologic diagnosis)

102/102 (mean 58y)

Nulliparous

1.0 (ref.)

Same hospital, time at diagnosis, age, marriage status

Parous

0.65 (0.45–0.92)

1–2

0.81 (0.55–1.20)

3–4

0.59 (0.39–0.88)

≥5

0.58 (0.38–0.91)

(Trained interviewer/pathology confirmation)

242/1021 (20–79y)

Nulliparous

1.0 (ref.)

Age, BMI, hypertension, diabetes

Parous

0.43 (0.34–0.54)

1–3

0.23 ((0.16–0.34)

≥4

0.33 (0.23–0.48)

(Medical record/histology comfirmation)

5382/72127 (30–84y)

Nulliparous

1.0 (ref.)

Age

Parous

0.81 (0.76–0.86)

1

0.92 (0.85–0.99)

2

0.83 (0.77–0.88)

≥3

0.71 (0.66–0.77)

(Database/Cancer Registry)

283/566 (33–74y)

Nulliparous

1.0 (ref.)

age

Parous

0.85 (0.69–1.05)

1

0.77 (0.58–1.01)

≥2

0.89 (0.72–1.11)

(Trained interviewer/histology confirmation)

282/282 (31–82y)

Nulliparous

1.0 (ref.)

Age, weight, social class

Parous

0.95 (0.79–1.15)

1–2

0.89 (0.72–1.10)

3–4

1.06 (0.84–1.32)

≥5

1.02 (0.72–1.44)

(Trained interviewer/histology confirmation)

191/419 (NA)

Nulliparous

1.0 (ref.)

Age, area, BMI

Parous

0.40 (0.26–0.61)

1

0.40 (0.22–0.74)

2

0.39 (0.25–0.61)

≥3

0.44 (0.24–0.79)

(questionnaire/histology confirmation)

421/1263 (22–84y)

Nulliparous

1.0 (ref.)

Age, area

Parous

0.223 (0.115–0.435)

(questionnaire/cancer registry)