Table 1.

Characteristics of included studies

Author	Year	State	Study design	No of cases	No of hospital units	Year of data collection	Population	Sampling	Type of CS analysed
Stafford20	1990	California	Cross-sectional	461 066	Not reported	1986	Primipara and multipara; any risk	Consecutive	Any
Haas et al 15 A	1993	Massachusetts	Cross-sectional	57 257	Not reported	1984	Primipara and multipara; any risk	Consecutive	Any
Haas et al 15 B	1993	Massachusetts	Cross-sectional	64 346	Not reported	1987	Primipara and multipara; any risk	Consecutive	Any
Braveman et al 209	1995	California	Retrospective cohort	213 761	Unclear	1991	Primipara; no previous CS; any risk	Consecutive	Any
Burns et al 21	1995	Arizona	Cross-sectional	33 233	36	1989	Primipara and multipara; any risk	Consecutive	Any
Onion et al 210 A	1999	Maine	Cross-sectional	41 177	Not reported	1990–1992	Primipara; no previous CS; any risk	Consecutive	Any
Onion et al 210 B	1999	New Hampshire	Cross-sectional	41 401	Not reported	1990–1992	Primipara; no previous CS; any risk	Consecutive	Any
Onion et al 210 C	1999	Vermont	Cross-sectional	19 077	Not reported	1990–1992	Primipara; no previous CS; any risk	Consecutive	Any
Aron et al 211	2000	Ohio	Retrospective cohort	25 697	21	1993–1995	Primipara; no previous CS; any risk	Consecutive	Any
Grant22 A	2005	All states	Cross-sectional	9017	Not reported	1988	Primipara and multipara; any risk	Random	Any
Grant22 B	2005	Florida	Cross-sectional	147 821	Not reported	1992	Primipara and multipara; any risk	Consecutive	Any
Coonrod et al 62	2008	Arizona	Cross-sectional	28 863	40	2005	Primipara; low risk	Consecutive	Any
Huesch212	2011	New Jersey	Cross-sectional	182 108	Not reported	2004–2007	Primipara and multipara; no previous CS; low risk	Consecutive	Planned
Kozhimannil et al 103	2014	All states	Cross-sectional	6 717 486	Over 1000	2002–2009	Primipara and multipara; any risk	Random	Any
Huesch et al 213	2014	California	Cross-sectional	408 355	254	2010	Primipara and multipara; no previous CS; any risk	Consecutive	Planned
Sebastião et al 214	2016	Florida	Retrospective cohort	412 192	122	2004–2011	Primipara; no previous CS; low risk	Consecutive	Emergency

CS, caesarean section.