|
Characteristics
|
Number of studies
|
Summary RR (95% CI)
|
P-for-difference
|
P-for-heterogeneity
|
I
2(95% CI)
|
|---|
|
All studies
|
9
|
1.13 (1.06 to 1.21)
| |
<0.01
|
82.4 (65.4 to 89.1)
|
|
Region
| | | | | |
|
United States
|
4
|
1.20 (0.95 to 1.52)
|
Ref.
|
0.01
|
75.5 (32.3 to 91.1)
|
|
Europe
|
5
|
1.12 (1.05 to 1.19)
|
0.60
|
<0.01
|
87.2 (69.2 to 92.7)
|
|
Year of publication
| | | | | |
|
In or after 2000
|
5
|
1.10 (1.04 to1.16)
|
0.29a
|
0.07
|
53.9 (0.0 to 81.0)
|
|
Before 2000
|
4
|
1.27 (1.02 to 1.58)
| |
<0.01
|
89.1 (74.8 to 95.3)
|
|
Study population
| | | | | |
|
≥2,500
|
6
|
1.11 (1.04 to1.18)
|
Ref.
|
<0.01
|
86.0 (68.9 to 91.8)
|
|
<2,500
|
3
|
1.28 (1.14 to 1.44)
|
0.25
|
0.45
|
0.0 (0.0 to 89.6)
|
|
Study design
| | | | | |
|
Cohort
|
8
|
1.11 (1.04 to 1.18)
|
Ref.
|
<0.01
|
81.0 (59.1 to 88.7)
|
|
Nested case-control
|
1
|
1.33 (1.16 to 1.52)
|
0.21
|
-
|
-
|
|
Exposure
| | | | | |
|
Caffeine
|
7
|
1.13 (1.06 to 1.21)
|
Ref.
|
0.01
|
67.4 (0.0 to 83.4)
|
|
Coffee
|
2
|
1.16 (0.91 to 1.48)
|
0.93
|
<0.01
|
91.9 (NA)
|
|
Outcome
b
| | | | | |
|
LBW
|
5
|
1.12 (1.02 to 1.23)
|
Ref.
|
<0.01
|
75.8 (40.6 to 90.1)
|
|
IUGR
|
5
|
1.12 (1.00 to 1.25)
|
0.78
|
0.04
|
59.5 (0.0 to 82.8)
|
|
SGA
|
2
|
1.13 (1.07 to 1.18)
|
0.85
|
0.14
|
53.9 (NA)
|
|
Age
c
| | | | | |
|
<30 years
|
4
|
1.17 (1.05 to 1.31)
|
Ref.
|
<0.01
|
88.6 (73.4 to 95.1)
|
|
≥30 years
|
5
|
1.13 (1.08 to 1.19)
|
0.54
|
0.32
|
15.1 (0.0 to 69.2)
|
|
Method of exposure assessment
| | | | | |
|
Interviewer-based
|
5
|
1.17 (1.01 to 1.36)
|
Ref.
|
0.01
|
68.2 (17.9 to 87.7)
|
|
Self-administered
|
3
|
1.08 (1.01 to 1.16)
|
0.42
|
<0.01
|
90.7 (70.5 to 95.2)
|
|
NA
|
1
|
1.33 (1.16 to 1.52)
|
0.38
|
-
|
-
|
|
Exposure period assessed
b
| | | | | |
|
First trimester
|
3
|
1.17 (0.90 to 1.53)
|
Ref.
|
<0.01
|
83.0 (48.0 to 94.4)
|
|
First to second trimesters
|
2
|
1.09 (0.99 to 1.21)
|
0.62
|
<0.01
|
95.3 (NA)
|
|
Whole pregnancy
|
2
|
1.13 (1.04 to 1.24)
|
0.99
|
0.40
|
0.0 (NA)
|
|
Third trimester
|
2
|
1.06 (1.00 to 1.12)
|
0.64
|
0.63
|
0.0 (NA)
|
|
NA
|
1
|
1.33 (1.16 to 1.52)
|
0.51
|
-
|
-
|
|
Adjustment for smoking
d
| | | | | |
|
Fine
|
7
|
1.12 (1.04 to 1.20)
|
Ref.
|
<0.01
|
82.0 (59.1 to 89.6)
|
|
Crude
|
2
|
1.24 (0.89 to 1.72)
|
0.52
|
<0.01
|
91.7 (NA)
|
|
Median population caffeine intake
| | | | | |
|
<200 mg/d
|
5
|
1.15 (1.05 to 1.26)
|
0.32a
|
0.02
|
66.7 (0.0 to 85.1)
|
|
≥200 mg/d
|
3
|
1.10 (1.01 to 1.21)
| |
<0.01
|
83.9 (51.8 to 94.7)
|
|
NA
|
1
|
1.40 (0.84 to 2.32)
| |
-
|
-
|
-
a
P-value was obtained by modeling year of publication and median of assigned doses as continuous variables; btotal number of study is more than 9 because some studies reported additional (usable) results for a different outcome or exposure period; cmean age <30 years or ≥30 years. If mean age is not available, classification was based on whether the majority of the population (>50%) is <30 years or ≥30 years; dfine adjustment for smoking refers to studies that adjusted for amount of smoking or studies that adjusted for smoking using a biomarker; crude adjustment refers to studies that did not adjust for amount of smoking. I
2, I-squared; IUGR, intrauterine growth restriction; LBW, low birth weight; NA, not available; Ref., reference. RR, relative risk; SGA, small for gestational age.
