Prenatal Maternal Anxiety as a Risk Factor for Preterm Birth and the Effects of Heterogeneity on This Relationship: A Systematic Review and Meta-Analysis

Table 3

Classification of studies according to whether the primary outcome variable was PTB, spontaneous PTB, or gestational age and the type of statistic (odds ratio or correlation coefficient) used to estimate the relationship (top panel). The effect of excluding estimates of dubious quality on the heterogeneity of the estimates of the OR for anxiety and spontaneous PTB. There were three exclusion criteria: () the results of the study were numerically suspect; () the authors’ reported the odds ratio for a continuous predictor variable; () the odds ratio was inappropriately adjusted as described in Section 2.6 (lower panel).

Statistic	Odds ratio		Correlation coefficient
Outcome	SPTB	PTB	PTB	GA
Study	Andersson et al. (2004)  [24]; Dole et al. (2004) [31]; Kramer et al. (2009) [38]; Ibanez et al. (2012)  [37]; Peacock et al. (1995)  [46]; Sanchez et al. (2013)  [49]; Orr et al. (2007)  [44]; Copper et al. (1996) [29]; Dayan et al. (2006)  [30]	Berle et al. (2005) [25]; Field et al. (2010) [34]; Andersson et al. (2004)  [24]; Bindt et al. (2013)  [26]; Dole et al. (2004)  [41]; McDonald et al. (2014) [43]; Ibanez et al. (2012)  [37]; Amiri et al. (2010)  [23]; Catov et al. (2010)  [27]; Powell et al. (2013)  [47]; Perkin et al. (1993)  [20]; Martini et al. (2010)  [22]; Rauchfuss and Maier (2011) [21]	Glynn et al. (2008)  [35]; Lobel et al. (2008)  [40]; Wadhwa et al. (1993) [50]	Bindt et al.(2011) [26]; Wadhwa et al. (1993)  [50]; Dominguez et al. (2005) [33]; Dominguez et al. (2008) [32]; Mancuso et al. (2004) [42]; Rini et al. (1999) [48]; Lobel et al. (2008)  [40]; Pagel et al. (1990) [45]; Lobel et al. (2000) [41]; Hosseini et al. (2009)  [36]
Heterogeneity
Before exclusion	76.0%,	79.8%,	61.9%,	0.0,
After exclusion	46.9%,	0.0%,

Goldenberg et al. [19] study (1996) was excluded since it was not possible to extract any relevant information and Latendresse and Ruiz [39] (2011) only provided information on the mean (SD) anxiety scores in the mothers of preterm and those of term babies.
Studies that provided adjusted estimates but not in the same form as the unadjusted estimate (i.e., for categorical rather than binary) so the unadjusted estimate was used.
Studies that reported the OR for a continuous predictor variable (excluded).
Studies that used inappropriate adjustment in the multivariable analysis and no unadjusted estimate available (excluded).
Studies that were numerically suspect (excluded).