Table 2 Adjusted OR/RR and confidence interval of factors significantly associated with birth spacing

 At first pregnancy (years)

de Jonge 2014

18.3 vs 18.6

< 33

0.92–0.98

 At delivery of the last child (years)

Hailu 2016

17–24 vs > 34

< 36

0.36–2.66

25–29 vs > 34

0.40–2.0

30–34 vs > 34

1.08–5.15

de Jonge 2014

22 vs 22.88

< 33

1.08–1.15

 Of the mother (years)^a

Chirwa 2014

15–19 vs 45–49

< 25

1.56–4.04

20–24 vs 45–49

1.27–2.52

25–29 vs 45–49

0.93–1.84

30–34 vs 45–49

0.89–1.76

35–39 vs 45–49

0.74–1.5

40–44 vs 45–49

0.69–1.44

 Of the mother (years)^b

Begna 2013

20–24 vs 25–29

< 36

0.53–3.48

30–34 vs 25–29

0.39–1.17

35–39 vs 25–29

0.17–0.6

40–44 vs 25–29

0.10–0.49

45–49 vs 25–29

0.15–1.01

Muganyizi 2013

30 vs 15–29

< 24 or > 60

0.5–1.7

Exavery 2012

15–19 vs 45–49

< 33

9.63–19.35

20–24 vs 45–49

3.16–5.86

25–29 vs 45–49

1.77–3.26

30–34 vs 45–49

1.52–2.8

35–39 vs 45–49

1.21–2.24

40–44 vs 45–49

0.95–1.83

Ismail 2008

One-year increase in age

< 24

0.8–0.92

Ngianga-Bakwin 2005

< 21 vs > 21 and < 35

< 24

0.55–0.62

> 35 vs > 21 and < 35

0.62–0.72

 Of the woman’s own mother at first pregnancy (years)

Atkin 1992

11–17 vs > 17

< 24

Not provided

 Duration (months)

Hailu 2016

12–23 vs > 23

< 36

31.61–114.59

Begna 2013

<  25 vs > 24

< 36

6.97–136.19

Ismail 2008

< 12 vs > 11

< 24

3.59–10.62

 Type

Chirwa 2014

Exclusive breastfeeding vs Mixed

< 25

1–1.17

Never breastfeeding vs Mixed

0.99–1.15

Ngianga-Bakwin 2005

Exclusive breastfeeding vs No breastfeeding

< 24

0.58–0.78

Mixed feeding vs No breastfeeding

0.82–0.90

 Method

Chirwa 2014

Not using contraception vs Modern method

< 25

0.85–1.08

Ngianga-Bakwin 2005

Using injections vs Using other methods

< 24

1.1–1.38

Atkin 1992

Postpartum IUD: No/Yes

< 24

Not provided

 Use

Hailu 2016

No vs Yes

< 36

1.68–5.39

Muganyizi 2013

No vs Yes

< 24 or > 60

0.6–1.8

Begna 2013

No vs Yes

< 36

4.02–8.69

Ismail 2008

No vs Yes

< 24

2.21–7.05

Ngianga-Bakwin 2005

No vs Yes

< 24

0.82–0.93

Todd 2008

Prior contraceptive use: Yes/No

Longer mean birth interval (2.21 ± 0.79 Vs 2.01 ± 0.87 years)

1.12–1.40

Hailu 2016

No formal education vs Has formal education

< 36

1.8–6.43

Chirwa 2014

No education vs Secondary or higher

< 25

0.97–1.19

Primary education vs Secondary and higher

1–1.16

de Jonge 2014

Secondary or above vs None or primary education

< 33

1.09–1.45

Begna 2013

No formal education vs Formal education

< 36

1.15–3.37

Muganyizi 2013

Primary vs No education

< 24 or > 60

0.2–4.6

Secondary or above vs No education

0.3–7.3

Exavery 2012

Never been to school vs Secondary/higher

< 33

1.01–1.60

Primary vs Secondary/higher

0.87–1.37

Ngianga-Bakwin 2005

No education vs Secondary education or higher

< 24

1.06–1.26

Primary education vs Secondary education or higher

1.03–1.20

Sirivong 2003

Literate vs Illiterate

Birth spacing (length not specified)

0.08–0.84

Muganyizi 2013

Not in marriage vs In marriage

< 24 or > 60

0.4–2.1

Exavery 2012

Previously married (widowed or divorced) vs Married

< 33

0.48–0.66

Single vs Married

0.57–0.73

Atkin 1992

Women who were in a legal or consensual union at 5 months: Yes / No

< 24

Not provided

 Intervention

Abdullah 2018

Intervention: integrated post-partum family planning and maternal and newborn health. Control: maternal and newborn health only.

< 24

0.69–0.95

 Occupational group

de Jonge 2014

Tea garden resident: Yes vs No

< 33

1.07–1.87

 Religion

Other vs Muslim

0.53–0.87

 Time period

Ngianga-Bakwin 2005

1998–2001 vs 1991–1993

< 24

0.84–0.95

 Husband

Begna 2013

Daily worker vs Animal husbandry

< 36

1.01–4.79

Farmers vs Animal husbandry

0.24–1

Merchant vs Animal husbandry

0.36–1.43

Others vs Animal husbandry

0.47–5.92

 Mother

Hailu 2016

Farmer vs Others

< 36

0.31–23.23

Housewife vs Others

0.17–5.86

Merchant vs Others

0.16–13.24

Muganyizi 2013

Employment Business vs Salary employment

< 24 or > 60

0.6–2.1

Employment Housewife/others vs Salary employment

0.7–3.4

de Jonge 2014

> 3 vs 1

< 33

0.19–0.41

2 vs 1

0.44–0.63

3 vs 1

0.29–0.51

Muganyizi 2013

> 3 vs 2

< 24 or > 60

0.9–3.7

3 vs 2

0.5–1.5

Begna 2013

2 vs > 4

< 36

1.50–9.25

3&4 vs > 4

1.23–5.92

Exavery 2012

> 3 vs 2

< 33

2.25–2.85

3 vs 2

1.19–1.40

Ismail 2008

Parity (no further explanation)

< 24

1.22–1.76

 Outcome

de Jonge 2014

Adverse outcome of any previous pregnancy: Yes / No

< 33

1.83–2.40

Muganyizi 2013

Immediate past pregnancy loss: Yes / No

< 24 or > 60

1.3–4.7

Exavery 2012

Birth: Multiple vs Singleton

< 33

0.57–0.96

Ismail 2008

History of abortion: Yes vs No

< 24

0.02–0.34

 Place of delivery

Hailu 2016

Health institution vs Home

< 36

0.61–3.8

Exavery 2012

Elsewhere vs Health facility

< 33

1.71–2

 Planned

Hailu 2016

No vs Yes

< 36

0.9–2.61

Hailu 2016

Female vs Male

< 36

3.65–12.63

Begna 2013

Female vs Male

< 36

1.17–2.52

 Household assets^c

de Jonge 2014

0–3 vs > 3

< 33

1.22–1.65

 Income

Hailu 2016

Wealth index: Fourth vs Richest

< 36

1.41–11.13

Wealth index: Middle vs Richest

1.39–11.38

Wealth index: Second vs Richest

2.26–8.48

Wealth index: Poorest vs Richest

4.65–44.15

Chirwa 2014

Low vs High

< 25

0.8–1.01

Middle vs High

0.77–0.94

Ngianga-Bakwin 2005

Low vs High

< 24

1.10–1.26

Middle vs High

1.17–1.34

 Place of residence

Chirwa 2014

Rural vs Urban

< 25

0.97–1.13

Exavery 2012

Rural vs Urban

< 33

0.95–1.13

Ngianga-Bakwin 2005

Urban vs Rural

< 24

0.79–0.9