Table 2

Characteristics of the included primary studies

Number (%) of studies


Year of publication

1990-1994

8 (22)

1995-1999

9 (25)

2000-2004

15 (42)

2005-2008 (part year)

4 (11)

Country

USA

26 (72)

Australia

4 (11)

U.K.

4 (11)

Canada

1 (3)

Greece

1 (3)

Study design

RCT-individually randomized

7 (19)

RCT-cluster randomized

2 (6)

Retrospective cohort study

12 (33)

Prospective cohort study

6 (17)

Cohort study (unspecified)

2 (6)

Mixed retrospective/prospective cohort study

1 (3)

Before and after study

6 (17)

Outcomes reported*

PTB/preterm labour

32 (89)

Infant mortality

5 (14)

Neonatal mortality

6 (17)

Congenital anomalies

6 (17)


* Not mutually exclusive

Hollowell et al. BMC Pregnancy and Childbirth 2011 11:13   doi:10.1186/1471-2393-11-13

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