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

First author’s last name, publication year, Country, Study design		Cases/subject (age), duration of follow up	Parity categories (exposure/case assessment)	RR (95% CI)	Matched/Adjusted factors
Prospective studies
Setiawan, 2013,International, 10 cohort and 14 case-control studies		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)
Dossus, 2010, Europe, CS		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)
Wernli, 2006, China, CS		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 )
Hinkula, 2002, Finland, CS		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
Terry, 1999, Sweden, CS		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)
Albrektsen, 1995, Norway, CS		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)
Kvale, 1988, Norway, CS		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)
PLCO, US, CS		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)
USRT, US, CS		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)
de Warrd, 1996, Netherlands, CS		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)
Bevier, 2011, Sweden, CS		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)
First author, publication year, Country, Study design		Cases/control (age)	Parity categories (exposure/case assessment)	RR (95% CI)	Matched/Adjusted factors
Case-control studies
Parslov, 2000, Denmark, PC-CS	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)
Salazar-Martinez, 1999, Mexico, HC-CS	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)
Parazzini, 1998 Italy, HC-CS	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)
Kalandidi, 1996, Greece, HC-CS	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)
Shu, 1993, China, PC-CS	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)
Koumantaki, 1989, Greece, HC-CS	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)
Kelsey, 1982, US, HC-CS	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)
Baron, 1986, US, HC-CS	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)
Castellsague, 1993, US, PC-CS	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)
Dahlgren, 1991, Sweden, PC-CS	147/1409 (31–65y)		Nulliparous	1.0 (ref.)	unadjusted
			parous	0.43 (0.31–0.60)
			(interview and/or questioinnaire/hospital records)
Damon, 1960, US, HC-CS	197/233 (NA)		Nulliparous	1.0 (ref.)	unadjusted
			parous	0.81 (0.66–0.995)
			(hospital records/pathology diagnosis)
Elwood, 1977, US, PC-CS	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)
Fox, 1970, US, PC-CS	300/300 (NA)		Nulliparous	1.0 (ref.)	age
			parous	0.74 (0.63–0.86)
			(records/histological confirmation)
Garnet, 1958, US, HC-CS	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)
Henderson, 1983, US, PC-CS	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)
Hirose, 1996, Japan, HC-CS	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)
Hosono, 2011, Japan, HC-CS	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)
Jaakkola, 2011, Finland, PC-CS	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)
Kakuta, 2009, Japan, HC-CS	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)
Lawrence, 1989, US, PC-CS	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)
Lesko, 1991, US, HC-CS	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)
Levi, 1991, Switzerland, HC-CS	122/309 (75y−)		Nulliparous	1.0 (ref.)	unadjusted
			Parous	0.84 (0.61–1.16)
			(Trained interviewer/histological confirmation)
Littman, 2001, US, PC-CS	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)
Macdonald, 1977, US, PC-CS	145/580 (unknown)		Nulliparous	1.0 (ref.)	age
			Parous	0.56 (0.38–0.83)
			(Medical record linkage/pathology confirmation)
Newcomer, 2001, US, PC-CS	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)
Pettersson, 1986, Sweden, PC-CS	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)
Spengler, 1981, Canada, PC-CS	88/177 (40–74y)		Nulliparous	1.0 (ref.)	age
			Parous	1.10 (0.65–1.86)
			(Trained interviewer/pathology confirmation)
Wynder, 1966, US, HC-CS	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)
Wang, 1990, China, HC-CS	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)
Hachisuga, 1998, Japan, HC-CS	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)
Brons, 2015, Denmark, PC-CS	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)
La Vecchia, 1984, Italy, HC-CS	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)
Salmi, 1979, Finland, PC-CS	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)
Asakura, 2009, Japan, PC-CS	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)
Hao, 2009, China, PC-CS	421/1263 (22–84y)		Nulliparous	1.0 (ref.)	Age, area
			Parous	0.223 (0.115–0.435)
			(questionnaire/cancer registry)

BMI: body mass index; CI: confidence interval; CS: cohort study; HC-CS: hospital-based case-control study; NA: not available; NC-CS: nested case-control study; OR: odds ratio; PC-CS: population-based case-control study; ref.: reference; RR: relative risk.