Table 4.
Estimated total effect and standardised mediator effect (proportion eliminated by mediation) from included studies (n = 22)
| Paper | Effect of SES on PTB (95% confidence interval if available) | Mediator | Prevalence of mediator in sample | Proportion eliminated (95% confidence interval if available) |
|---|---|---|---|---|
| Poulsen et al. (2019) [33] Denmark | Total effect RD: 2.0 (1.4, 2.5) excess PTB/100 singleton deliveries | Smoking | 17% total; 39% short education, 8% long | 22% (11%, 31%)a |
| Poulsen et al. (2019) [33] Netherlands | Total effect RD: 3.2 (0.8, 5.2) | 19% total; 41% short education, 7% long | 10% (-22%, 29%) | |
| Poulsen et al. (2019) [33] Norway | Total effect RD: 2.0 (0.9, 3.0) | 9% total; 34% short education, 4% long | 19% (-1%, 29%)a | |
| Ross et al. (2019) [34] | Direct coefficient: 0.072* Total effect coefficient 0.077 | Pre-eclampsia | 5% in black women, 3% in white women | 6.5%a |
| Dolatian et al. (2014) [35] | Direct coefficient: 0.06* Total effect coefficient: 0.06126* | Perceived stress | Mean | 11.8%a |
| Perceived social support through stress | Mean | Mediated effect in opposite directiona | ||
| Combined | 2.1%a | |||
| Clayborne et al. (2017) [36] | Total effect OR: 0.91 (0.64, 1.31) | Pre-pregnancy body mass index (BMI) | Mean | Cannot be estimated |
| Gestational weight gain | Mean | Cannot be estimated | ||
| Combined | Cannot be estimateda | |||
| Dooley (2009) [37] (PhD thesis) | Direct effect: 43.29% increase in odds/standard deviation increase. Total effect**: 46.01%* | Medical risk | 13% | 2.9%a |
| Smoking | 13% | 3.0%a | ||
| Perceived neighbourhood support | Mean | No indirect effect | ||
| Mehra et al. (2019) [38] | Direct effect coefficient: 0.036. Total effect coefficient: 0.059* | Hypertension | 10% | 22.0%a |
| Infection | 28% | 16.9%a | ||
| Meng et al. (2013) [39] | Total effect coefficient: 0.981 (0.626–1.337) | SES-related support | Composite measure | 11.7%a |
| Psychosocial | Composite measure | 2.1%a | ||
| Behavioural | Composite measure | 5.5%a | ||
| Health | Composite measure | 6.4%a | ||
| Mirabzadeh et al. (2013) [40] | Total effect coefficient: 0.1441a | Perceived social support through stress | Mean | 8.1%a |
| Stress, depression, and anxiety | Mean | 22.5%a | ||
| Combined | 30.6%a | |||
| Misra et al. (2001) [41] | Total effect OR: 2.85 (1.85–4.40) | Psychosocial factors only | 26% severe stress | 44% |
| Biomedical and psychosocial factors | 5% chronic disease | 64% | ||
| Nkansah-Amankra et al. (2010) [42] | Total effect OR 1.34 (0.80–2.25) | Maternal stress (emotional, financial, spousal-related, traumatic) | 14% low poverty, 57% high poverty | No significant total effect |
| Räisänen et al. (2013) [43] | Total effect OR: Extremely PTB 1.61 (1.38–1.89); Very PTB 1.48 (1.31–1.68); Moderately PTB 1.27 (1.22–1.32) | Smoking | 12% to 18% by gestational age category | 26% for extremely PTB 33% for very PTB 30% for moderately PTB |
| Other factors and smoking | Composite measure | 39% for extremely PTB 50% for very PTB 41% for moderately PTB | ||
| Ahern et al. (2003) [44] African-American | Total effect parameter estimate proportion unemployed: 44.4* | Cigarettes per day | Mean | 3% |
| Ahern et al. (2003) [44] White | Total effect parameter estimate change in unemployed: -3.32 | No significant total effect | ||
| Amegah et al. (2013) [45] | Total effect RR: 1.83 (1.31–2.56) | Malaria infection during pregnancy | 48% | No effect |
| Pre-pregnancy BMI | 33% healthy weight | 17% | ||
| Cooking fuel used | 18% LPG, 24% charcoal, 5% firewood | 22% | ||
| Combined | 30% | |||
| van den Berg et al. (2012) [46] | Total effect OR: 1.95 (1.19–3.20) | Smoking | 7% total, 33% in low educated, 2% in high educated | 43% |
| Smoking and environmental tobacco exposure | 6% total, 27% in low educated, 1% in high educated | 39% | ||
| Morgen et al. (2008) [47] | HR primiparous: 1.22 (1.04–1.42) HR multiparous: 1.56 (1.31–1.87) | Smoking | 26% to 35% by gestational age category | 5% in primiparous 23% in multiparous |
| Alcohol | 40% to 45% by gestational age category | 5% in primiparous 4% in multiparous | ||
| Binge drinking | 25% to 26% by gestational age category | 5% in primiparous no effect in multiparous | ||
| Pre-pregnancy BMI | Mean | 9% in primiparous 2% in multiparous | ||
| Gestational weight gain | Mean | 5% in primiparous 4% in multiparous | ||
| Combined | 23% in primiparous 30% in multiparous | |||
| Gisselmann and Hemström (2008) [48] | Total effect OR: 1.41* | Job control | Not stated | 44% |
| Job hazards | Not stated | 5% | ||
| Physical demands | Not stated | 22% | ||
| All working conditions | Not stated | 46% | ||
| Niedhammer et al. (2012) [49] | Total effect HR: 2.14 (1.05–4.38) | Rented home | 43% lower than secondary, 15% higher than secondary | 26% |
| Crowded home | 18% lower than secondary, 5% higher than secondary | 13% | ||
| Material factors | Composite | 33% | ||
| Smoking | 46% lower than secondary, 16% higher than secondary | 2% | ||
| Alcohol | 50% lower than secondary, 62% higher than secondary | 14% | ||
| Behavioural | Composite | 10% | ||
| Saturated fatty acids (nutritional factors) | 31% lower than secondary, 20% higher than secondary | 14% | ||
| Material + behavioural | Composite Measure | 38% | ||
| Material + behavioural + nutritional | Composite Measure | 42% | ||
| Jansen et al. (2009) [50] | Total effect OR: 1.89 (1.28–2.80) | Mother’s age | Mean | 22% |
| Mothers’ height | Mean | 22% | ||
| Preeclampsia | 2% total, 1% high, 4% low education | 13% | ||
| Intrauterine growth restriction (IUGR) | 1% total, 1% high, 2% low education | 12% | ||
| Marital status (single) | 8% total, 3% high, 20% low education | 2% | ||
| Pregnancy planning (unplanned) | 19% total, 10% high, 34% low education | No effect | ||
| Financial concerns | 12% total, 5% high, 30% low education | 19% | ||
| Long-lasting difficulties | Mean | 11% | ||
| Psychopathology | Mean | 16% | ||
| Working hours | Mean | No effect | ||
| Smoking | 18% total, 5% high, 45% low education | 8% | ||
| Alcohol consumption | 50% total, 68% high, 25% low education | 17% | ||
| BMI | 67% total healthy weight, 75% high, 51% low education | 7% | ||
| All except preeclampsia/IUGR/ working hours/pregnancy planning | Composite Measure | 69% | ||
| All except working hours/pregnancy planning | Composite Measure | 89% | ||
| Quispel et al. (2014) [51] | Total effect OR: 1.06 (1.02–1.10) | Depression score | 15% | No effect |
| Gissler et al. (2003) [52] | Total effect OR: 1.35 (1.25–1.45) | Smoking | 15% total, 5% upper white collar, 26% blue collar workers | 42% |
| Gray et al. (2008) [53] | Total effect OR: 1.49 (1.43–1.54) | Smoking | For 2 periods: 30% & 29% total, 15% for both periods in least deprived, 43% & 39% in most deprived | 45% |
| de Oliveira et al. (2019) [54] | Direct standardised estimate: -0.083 | Inadequate prenatal care | Not stated | Cannot be estimateda |
| Unwanted pregnancy | Cannot be estimateda |
* p value < 0.05, ** Percentage change in the odds per standard deviation increase
a indirect effect significant, PTB preterm birth, HR hazard ratio, OR odds ratio, RR relative risk, RD risk difference, coefficient = beta coefficient, LPG liquefied petroleum gas, Mean mean score so prevalence score not calculable