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Table 1 Table of included studies

From: Maternal smoking and the risk of still birth: systematic review and meta-analysis

Reference Author year Study type Population Location Exposure: smoking during pregnancy and validity Definition of stillbirth (outcome) and gestational period Estimates Factors adjusted for in individual studies if available
Studies included in meta-analysis
12 Wood et al (2009) Cohort 158,502 Alberta Perinatal Health Program, 1991-2004 Canada Smokers: Yes Fetal death after at least 24 completed weeks of gestation. Adjusted OR 1.04 (0.74-1.47) Maternal age, diabetes, hypertension, previous caesarean section.
Not validated
13 Smith et al (2007) Cohort 84,769 Scotland morbidity records 1991-2001, UK Smokers: Yes Fetal death after at least 24 completed weeks of gestation. OR for smoking was calculated 2.15 (95% CI 1.74-2.65) Age, deprivation, height, BMI, Marital Status.
Not validated
14 Hogberg and Cnattingius (2007) Cohort 526,691 Sweden – Swedish National study 1983-2001- Participants with two consecutive pregnancies. Smokers: Yes Fetal death after at least 28 completed weeks of gestation. OR for smoking in both Pregnancies 1.35 (1.15-1.58). 1-9cig/day OR 1.16 (0.92-1.46) ≥10 cig/day 0R 1.55 (1.17-2.04). OR for smoking in the 1st pregnancy only OR 1.02 (0.79-1.30), 1-9 cig/day OR 1.13 (0.9-1.39), ≥10 cig/day OR 1.14 (0.87-1.51). OR for smoking in 2nd pregnancy only 0.84 (0.55-1.26), 1-9cig/day OR 1.10 (0.89-1.35), ≥ 10 cig/day OR 1.45 (1.16-1.81). Maternal age, education, cohabiting with infant’s father, mother’s country of birth, year of second delivery, inter-pregnancy interval and stillbirth in first pregnancy.
1-9 cig/day, ≥10 cig/day.
Not validated
26 Salihu et al (2008) Case control 1,444,378 USA – Missouri 1978-1997. Smokers: Yes In-utero fetal death at least 20 week into gestation. a) Bidirectional case cross-over OR 1.20 (1.03-1.39) 1-9 cig/day OR 1.16 (0.88-1.53) 10-19 cig/day OR 1.10 (0.90-1.24) ≥ 20 cig/day OR 1.21 (1.01-1.50), Maternal race and age.
1-9 cig/day,
10-19 cig/day, b) Case Control OR 1.34 (1.26-1.43) 1-9 cig/day OR 0.94 (0.76-1.70) 10-19 cig/day OR 1.31(1.22-1.41) ≥20 cig/day OR 1.43 (1.31-1.54).
≥20 cig/day.
Not validated
34*** Ahlenius and Thomassen (1999) Cohort 94,270 in 1984 and 124,201 in 1991. Sweden - Using the Swedish medical birth register in 1984 and 1991 Smokers: Yes. Death of a fetus before or during delivery with a gestational duration of at least 28 weeks. Combined (1984 and 1991) OR 1.37 (1.17 to 1.61) Maternal age and parity.
1-9 cig/day, ≥10 cig/day. 1-9 Cig/day OR 1.22
(1.00-1.48)
Not validated ≥10 Cig/day OR 1.62 (1.31-2.00)
1991 OR
1.47 (1.19 to 1.82)
>10 Cig/day OR 1.97 (1.51-2.59)
36*** Aliyu et al (2007) Cohort 1,436, 725 USA Missouri – Using Missouri maternally linked cohort data 1978 – 1997 Smokers: Yes In utero fetal death at < = 20 weeks gestation OR(originally presented as HRs) 1.43 (1.36-1.51) N/A*
1-9 cig/day, 10-19 cig/day, ≥ 20 cig/day.
Not validated
37 Gray et al (2009) Cohort 532,016 UK- Scotland, National study 1994-2003. Smokers: Yes. 24-44 weeks’ gestation OR 1.75 (1.61-1.91) N/A*
Not validated
38 McCowan et al (2007) Cohort 69,173 New Zealand - National Women’s Smokers: Yes Birth of a baby with no signs of life delivered at ≥ OR 1.33 (0.99-1.79) Infant sex, maternal ethnicity, parity, marital status, maternal age at delivery, history of previous miscarriage, history of previous abortion, previous low-birth weight infant, previous C-section.
Hospital, Auckland, New Zealand from 1993 to 2000 Not validated 20 weeks or with a birth weight of > 400 g if gestation was not known.
39 Miller et al (2010) Cohort 359,747 Canada – Ontario state 2004-2006 Smokers: Yes Death of fetus at 20 weeks of gestation Overall OR 1.58 (1.38-1.81) Age, parity, multiple gestation
Not validated
40 Moshin et al (2005) Cohort 433,227 Australia – New South Wales 1998-2002 Smokers: Yes Fetal death at ≥ 20 weeks gestation or of 400 g or more birth weight. Overall adjusted OR 1.17 (1.05–1.31) Unadjusted OR 1.05 (0.94–1.17). Maternal age, maternal country of birth, socioeconomic status, maternal diabetes mellitus, and first antenatal care visit.
Not validated
17*** Raymond et al (1994) Cohort 638,242 Sweden National study 1983-1989 Smokers: Yes Fetus death at 28 weeks of gestation or more. OR 1.4 (1.2-1.4) Age, parity, pregnancy complications, hypertensive diseases, diabetes, placental complications and intrauterine growth retardation (IUGR).
Not validated
42 Reddy et al (2006) Cohort 174,809 USA – 12 clinic centres and 19 hospital sites. 2002-2008. Smokers: Yes Fetal death at 23 weeks gestation and beyond. OR (originally presented as HRs) 1.57 (1.21-2.02) N/A*
Not validated
43 Sutan et al (2010) Cohort 541,811 UK- Scotland, National study (NHS Hospital) Smokers: Yes Late fetal death from 20 weeks gestation. OR 1.64 (1.46-1.84) Non stated
Not validated
44 Tuthill et al (1999) Cohort 16,047 Wales – All Wales Perinatal Survey 1993-1995 Smokers: Yes Mortality from 20 completed weeks of gestation OR 1.72(1.38-2.13) Social class, infection, placental abruption, sudden infant death syndrome.
Not validated
45 Wisborg et al (2001) Cohort 25,102 Denmark – Aarhust University Hospital 1989-1996. Smokers: Yes Delivery of a dead fetus occurring at 28 weeks or more gestation. OR 1.9 (1.3-2.9), Sex of child, parity, maternal age, education, alcohol, caffeine intake.
1-9 cig/day, ≥10 cig/day. 1-9 cig/day OR 1.5 (0.9-2.4) ≥10 cig/day 1.8 (1.2-2.8)
Not validated
46 Winbo et al (2001) Cohort 1,412,747 Sweden – National study 1983 - 1995 Smokers: Yes Death of fetus after competing 28 weeks of gestation. OR stillbirths ≥37 weeks compared with live births 1.08 (0.96-1.22) Non stated
Not validated
27 Ferraz and Gray (1991) Case control 11,483 Brazil – Natal city and state of Rio Grande do Norte 1984-1986 Smokers: Yes Stillborn cases weighing 500 g or more OR 1.4 (1.0-2.0) Non stated
Not validated
29 Dodds et al (2006) Case control 494 Canada – Nova Scotia and Eastern Ontario 1999-2001 Smokers: Yes Not specified - Death before delivery of a fetus weighing 500 g or more OR (originally presented in HRs) Smoking during 1st trimester 2.13 (1.23-3.64) N/A*
Not validated
30 Efkarpidis et al (2004) Case control 599 UK – Nottingham City Hospital 1991-1997. Smokers: Yes Definition of stillbirth not stated- pregnancies considered from ≥ 24 weeks OR 1.2 (0.64-1.6) Non stated
Not validated
31 Froen et al (2002) Case control 598 Norway – Oslo 1986-1995. Smokers: Yes Intrauterine death before onset of labour of a fetus > =22 weeks gestation or > = 500 g body mass OR calculated Using Stats 1.81 (1.02-3.15) 1-9 cig/day OR 1.0 (0.43-2.12), ≥10 cig/day 0R 3.04 (1.13-8.19) N/A*
1-9 cig/day, ≥10 cig/day.
Not validated
32 Goy et al (2008) Case control 510 Canada – Nova Scotia and Eastern Ontario 1999-2001. Smokers: Yes Not specified - Death before delivery of a fetus weighing 500 g or more OR 2.06 (1.22-3.47) Province of origin, age, inactivity during pregnancy, stillbirth in previous pregnancy, used fertility treatment
Not validated
33 Little and Weiberg (1993) Case control 4667 USA Smokers: Yes Fetal death at 28 weeks or more gestation OR calculated using Stata 1.29 (1.09-1.53) N/A*
1-19 cig/day, OR 1-19 cig/day 1.3 (1.09-1.57), 20-29 cig/day OR 1.39 (1.06-1.82), ≥30 cig/day OR 0.67 (0.41-1.12).
20-29 cig/day,
≥ 30 cig/day.
Not validated
47 Mishra et al (2005) Cross-sectional 16,802 India - Survey conducted 98-99 Smokers: Yes Delivery of a dead baby at > 28 weeks of pregnancy OR 1.23 (0.92-1.64) Cooking smoke, anaemia, BMI, education, standard of living, house type.
Not validated Unadjusted OR 1.60 (1.23-2.08).
48 Robson et al (2006) Cross-sectional 21, 880 Australia – New South Wales 1998-2003. Smokers: Yes Not stated OR 1.65 (1.15-2.38) Age, parity, medical/obstetric complications
1-10 cig/day >10 cig/day. 20 weeks 1- 10 cig/day OR 1.16 (0.80-1.69) >10 cig/day OR 1.68 (1.17-2.41).
Not validated
Studies included in narrative synthesis
16*** Cnattingius et al (1988) Cross-sectional 262,582 Sweden National Study – Using Swedish medical birth registry covering more than 99% of all births in Sweden. 1983-1985 Smokers: Yes Late fetal death – still birth occurring at 28 weeks of gestation or later OR (originally presented as RR) 1.37 (1.20-1.57) N/A*
1-9 cig/day, 1-9 cig/day 1.32 (1.12-1.55)
≥10 cig/day. ≥10 cig/day 1.45 (1.21-1.75)
Not validated
28*** Walles (1994) Case control 202 Sweden – 5 centres (Boras, Helsingborg, Karlskrona, Kristianstastad and Lund) 1983-1989. Smokers: Yes Definition of stillbirth not stated, pregnancies considered OR calculated using Stata. OR 1.18 (0.62-2.26) N/A*
1-10 cig/day, 1-10 cig/day OR 1.33 (0.58-3.09) >10 cig/day 1. 04 (0.43-2.50)
≥10 cig/day. ≥ 28 weeks
Not validated
35*** Aliyu et al (2008) Cohort 1,436,628 USA Missouri – Using Missouri maternally linked cohort data 1978 – 1997. Smokers: Yes. In utero fetal death at < = 20 weeks gestation. OR (originally presented as HRs) 1.48 (1.40-1.56) N/A**
< 35 years old, ≥ 35yers old. Not validated < 35 years smokers1.43 (1.35-1.51)
≥35 years Smokers OR 2.4 (2.06-2.80)
49 Kleinman et al (1988) Cohort 362,261 USA Missouri 1978-1983 Smokers: Yes (Fetal mortality) Fetal death at 20 weeks or more. OR Primiparas N/A**
< 1 pack/day ≥1 pack/day. <1 pack/day 1.36(1.16-1.59) ≥1 pack/day 1.62 (1.34-1.97)
Not validated   Multiparas
<1 pack/day 1.21 (1.06-1.38) ≥1pack/day 1.15(0.99-1.34)
50 Raatikainen et al (2006) Cohort 25,591 Finland-Kuopio University Hospital 1989-2001. Smokers: Yes. Fetal death was defined as intrauterine death before No estimates N/A**
Not validated
22 weeks of pregnancy or 500 g fetal weight.
51 Aliyu et al (2010) Cohort 633,849 US Missouri – Using Missouri maternally-linked cohort data files 1978 – 1997. Smokers: Yes In utero fetal death at > = 20 weeks gestation. Results HRs, N/A**
Not validated <15 years 3.3 (1.4-7.8), 15-19 years 1.7 (1.5-1.9), 20-24 years 1.5 (1.4-1.6)
No sufficient data to calculate Odds ratios.
52 Bai et al (2000) Cohort 7138 Australia- Liverpool hospital Sydney March 1996 to June 1998 Smokers: Yes Not Clear (births occurring at less than 20 weeks gestation age exclusion criteria). Results presented in Percentages. No odds ratios and no sufficient data to calculate OR. N/A**
Not validated
53 Huang et al (2000) Cohort 84,294 Canada – The Royal Victoria Hospital in Montreal 1961-1974 and 1978-1996. Smokers: Yes Fetal deaths occurring before labour without evidence of significant fetal, maternal or placental pathology weighing 500 g or more. No estimates N/A**
Not validated
18 Schramm (1997) Cross-sectional 176,843 USA – Missouri 1978-1990 Smokers: Yes Not validated Fetal death greater or equal to 20 weeks gestation. Results in RR no sufficient data to calculate OR N/A**
Smoking in 1st and not in 2nd pregnancy RR 1.11, Not smoking in 1st but in 2nd pregnancy RR 1.6.smoking in both pregnancies RR 1.19.
54 Salihu et al (2004) Cross-sectional 7,792,990 USA – 1995-1997. Smokers: Yes Intrauterine fetal demise after 20 weeks of gestation. Estimates in Hazard ratios not enough data to calculate OR. N/A**
Not validated ≥ 40 years 2.71 (1.88-3.91), 30-39 years 1.58 (0.96-2.60), 20-29 years 1.41 (1.16-1.71)
  1. OR – Odds Ratio, HR – Hazard Ratio, RR – Risk Ratio.
  2. N/A* - Original results were presented in HR/RR, OR was calculated using original data.
  3. N/A** - Studies included in descriptive synthesis only.
  4. *** - Studies using same dataset.
  5. Swedish National registry data set ref 16: 1933-1985, 17 and 28 : 1983-1989, ref 34: 1984 and1991.
  6. US – Missouri data set ref 35 and 36.