Table 3

Assessment of study quality through the Newcastle–Ottawa Scale

Case-control studySelectionComparability of cases and controlsExposure assessment
Bengtsson et al (1973)*****
Bertuccio et al (2007)***– (history of miscarriage)*
** (recurrent)
Kharazmi et al (2010)********
Winkelstein et al (1958)*****
Winkelstein et al (1964)****
Cohort studySelectionComparability of cases and controlsOutcome assessment
Cooper et al (1999)****
Gallagher et al (2011)*****
Kharazmi et al (2011)*******
Pell et al (2004)******
Smith et al (2003)******
  • The Newcastle–Ottawa Scale assesses study quality in three different areas, selection criteria, comparability of cases and controls, and exposure or outcome assessment. A maximum score of nine stars is allocated to each study: four for selection, two for comparability and three for exposure or outcome.