Table 2. Methodological quality of cohort studies included in the meta-analysis*.
| First author (reference), publication year | Representativenessof the exposed cohort | Selection of the unexposed cohort | Ascertainment of exposure | Outcome of interest not present at start of study | Control for important factor or additional factor† | Assessment of outcome | Adequacy of follow-up of cohorts‡ |
|---|---|---|---|---|---|---|---|
| Andriani, 2014 | ⚝ | ⚝ | ⚝ | — | ⚝⚝ | ⚝ | ⚝ |
| Qiu, 2014 | ⚝ | ⚝ | ⚝ | — | ⚝ | ⚝ | ⚝ |
| Miyake, 2013 | ⚝ | ⚝ | ⚝ | ⚝ | ⚝⚝ | ⚝ | ⚝ |
| Wu, 2007 | ⚝ | ⚝ | ⚝ | ⚝ | — | ⚝ | — |
| Wu, 2007 | ⚝ | ⚝ | ⚝ | ⚝ | — | ⚝ | ⚝ |
| Ward, 2007 | ⚝ | ⚝ | ⚝ | — | ⚝⚝ | ⚝ | ⚝ |
| Kim, 2005 | ⚝ | ⚝ | ⚝ | ⚝ | — | ⚝ | ⚝ |
| Jaakkola, 2001 | ⚝ | ⚝ | ⚝ | — | ⚝⚝ | ⚝ | ⚝ |
| Windham, 2000 | ⚝ | ⚝ | ⚝ | ⚝ | ⚝ | ⚝ | — |
| Pichini, 2000 | ⚝ | ⚝ | ⚝ | ⚝ | — | ⚝ | ⚝ |
| Sadler, 1999 | ⚝ | ⚝ | ⚝ | ⚝ | — | ⚝ | — |
| Ahluwalia, 1997 | ⚝ | ⚝ | ⚝ | — | ⚝ | ⚝ | ⚝ |
| Mathai, 1992 | ⚝ | ⚝ | ⚝ | ⚝ | — | ⚝ | ⚝ |
| Ahlborg, 1991 | ⚝ | ⚝ | ⚝ | ⚝ | ⚝⚝ | ⚝ | ⚝ |
| Lazzaroni, 1990 | ⚝ | ⚝ | ⚝ | — | — | ⚝ | ⚝ |
| Martin, 1986 | ⚝ | ⚝ | ⚝ | ⚝ | — | ⚝ | ⚝ |
* A study could be awarded a maximum of one star for each item except for the item Control for important factor or additional factor. The definition/explanation of each column of the Newcastle-Ottawa Scale is available from (http://www.ohri.ca/programs/clinical_epidemiology/oxford.asp.).
† A maximum of 2 stars could be awarded for this item. Studies that controlled for maternal age received one star, whereas studies that controlled for other important confounders such as body mass index, parity received an additional star.
‡ A cohort study with a follow-up rate >70% was assigned one star.