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Table 5
Table 5 Studies assessing the association of premature birth and the risk of breast cancer
Type of study	Author	Year	Design	Cases	Controls (or cohort)	Country/place of study	Gestational age (weeks)	OR (95% CI)	Comments

Case-control studies	[42]^a	1988	PCC	153	461	USA	25–32	1.16 (0.50–1.54)	Matched analysis
							33–40	Referent
	[13]^b	1996	NCC	571	1,525	USA	Categorical		Adjusted for age
							40	Referent
							38–39	0.76 (0.44–1.32)
							36–37	0.96 (0.59–1.56)
							Binomial
							≥ 37	Referent
							≤ 36	0.82 (0.37–1.82)
	[14]	1996	PCC	1123	1371	USA	Nonpreterm	Referent	Adjusted for age, menopausal status, and maternal smoking
							Preterm	1.1 (0.5–2.1)
	[32]^a	1997	NCC	1,010	2,625	Sweden	≥ 33	Referent	Adjusted for maternal age, matermal socioeconomic status, maternal parity, maternal pre-eclampsia or eclampsia, neonatal jaundice, severe prematurity, twin, and birth weight
							≤ 32	3.96 (1.46–10.81)
	[33]^b	1998	PCC	502	433	USA	≥ 43	1.5 (0.8–2.6)	Crude ORs
							37–42	Referent
							≤ 36	0.9 (0.5–1.8)
	[15]^a,b	2000	LCC	480	2,854	USA	≥ 37	Referent	Crude ORs
							33–36	1.34 (0.85–2.13)
							≤ 32	0.55 (0.19–1.57)
	[34]^a,b	2001	LCC	87	87	Sweden	≥ 40	8.4 (1.3–54.4)	Matched analysis by conditional logistic regression
							37–40	3.4 (0.7–17.0)
							33–36	3.5 (0.7–17.5)
							≤ 32	Referent
	[25]^a	2003	LCohort	127	(1,483)	Sweden	≥ 33	1.08 (0.64–1.70)	Standardized incidence ratio (expected/observed)
							≤ 32	0.92 (0.57–1.41)
	[45]^a,b	2004	LCC	2,471	9,801	USA	≥ 37	Referent	Adjusted for age and maternal age at first birth
							32–36	0.91 (0.72–1.13)
							≤ 31	1.43 (0.90–2.28)
	[20]^b	2005	PCC	1,424	1,457	Poland	≥ 37	Referent	Adjusted for age, education, age at menarche, menopausal status and age at menopause, age at first full-term pregnancy, number of full-term pregnancies, family history of breast cancer among first-degree relatives, mammography screening, and current body mass index
							≤ 36	1.01 (0.75–1.32)
Cohort studies	[62]^c	2000	LCohort	12	273	Sweden	35	0.2 (0.01–1.3)	Standardized incidence ratio
							33–34	0.7 (0.1–2.0)
							31–32	2.3 (0.7–5.3)
							<31	6.7 (1.4–19.5)
	[16]^c	2001	LTCCS	2,265	9,060	Sweden	33–36	Referent	Crude ORs
							37–38	1.8 (0.83–4.0)
							40–44	2.0 (0.88–4.6)
	[29]^c	2005	LCohort	367	5,346	Sweden	1 week increase	<50 years
								0.94 (0.83–1.07)
	[40]^c	2006	Cohort	97	5,847	USA	<39	0.77 (0.42–1.4)	Adjusted for age
							39	1.38 (0.78–2.4)
							40	Referent
							41+	1.33 (0.67–2.6)
	[31]^b	2006	Cohort	249	1024	USA	≥ 43	0.7 (0.2–2.7)	Adjusted for: age at diagnosis, diagnosis year, stage at diagnosis, and birth order, with exception of birth order, which is adjusted for maternal age
							37–42	Referent
							<37	1.4 (0.7–2.9)
								P for trend = 0.3

Cohort, cohort study; LCC, case-control study with linkage with population and cancer registry data; LTCCS, twin case-control study by using linkage with birth and cancer registry data; NCC, nested case-control study in cohort; PCC, population-based case-control study. ^aWe included this study in the meta-analysis with categories of ≥33 versus ≤32 months (reference). ^bWe included this study in the meta-analysis with categories of ≥37 versus ≤36 months (reference). ^cWe did not include these studies in the meta-analysis because they employed different categories or a continuous scale, or they did not provide the numbers of cases and controls in the report.
Park et al. Breast Cancer Research 2008 10:R8 doi:10.1186/bcr1850

Table 5