Table 1. Characteristics of the included studies.
| Author, year | Country | Study design | Size | GA(w) | BW(g) | Ascertainment of exposure; outcome | Risk of bias; quality | |
|---|---|---|---|---|---|---|---|---|
| Tsimis 2016 [13] | United States | Retrospective cohort | 374 | case:26.3±2.2 control:28.0±2.5 | case:868±237 control:993±276 | Medical records; cranial ultrasound 6 weeks after birth | No representativeness of the exposed cohort;NOS:8 | |
| Tawil 2012 [6] | Kingdom of Saudi Arabia | Case-control | 118 | case:27.4 control:26.2 | case:1019.0 control:824.3 | Medical records; cranial ultrasound at 1 week, 2 weeks and 5–6 weeks after birth | No representativeness of the cases, no report of non-response rate;NOS:7 | |
| Resch 2012 [14] | Austria | Case-control | 141 | case:30.3±2.3(25–35) control:30.4±2.4(24–35) | case:1450±550(618–2500) control:1446±358(685–2510) | Medical records; cranial ultrasound at days 1, 3, and 5 of life and repeated weekly until diagnosis | No representativeness of the cases, no report of non-response rate;NOS:7 | |
| Hatzidaki 2009 [12] | Greece | Case-control | 135 | case:30.1±2.6;control:30.4±2.4 | case:1278.4±428.2 control:1375.5±378.6 | Medical records; cranial ultrasound within 1 week after birth | No representativeness of the cases, no report of non-response rate;NOS:7 | |
| Bauer 2009 [11] | Austria | Case-control | 340 | case:31.1±2.5 control:31.3±2.5 | case:1278.4±428.2 control:1518±425 | Medical records; cranial ultrasound within 7 weeks after birth | No representativeness of the cases, no report of non-response rate;NOS:7 | |
| Oda 2008 [20] | Japan | Retrospective cohort | 30 | case:28.7±1.94 control:30.0±2.37 | case:1410±402 control:1525±525 | Medical records; cranial ultrasound before 72 hours and at 2 weeks after birth | No representativeness of the exposed cohort, follow-up was not long enough for outcome;NOS:7 | |
| Silva 2006 [10] | United States | Case-control | 352 | case:27.3±2.7 control:27.4±2.7 | case:958±306 control:1038±381 | Medical records; cranial ultrasound | No representativeness of the cases, no report of non-response rate;NOS:7 | |
| Murata 2005 [8] | Japan | Retrospective cohort | 201 | case:29.4±2.1 control:29.6±2.1 | case:1324±324 control:1304±371 | Medical records; cranial ultrasound within 4 weeks after birth | No representativeness of the exposed cohort, follow-up was not long enough for outcome;NOS:7 | |
| Locatelli 2005 [21] | Italy | Retrospective cohort | 196 | case:28.6±2.6 control:30.3±2.5 | case:1183±362 control:1502±489 | Medical records; cranial ultrasound at days 1, 3, and 7 of life and repeated every 2 weeks until 40 postconceptional weeks | No representativeness of the exposed cohort;NOS:8 | |
| Graham 2004 [9] | United States | Case-control | 150 | case:22.5±2.7 control:27.4±2.6 | case:1053±402 control:966±285 | Medical records; cranial ultrasound 6 weeks after birth | No representativeness of the cases, no report of non-response rate;NOS:7 | |
| Pladys 2001 [22] | France | Retrospective cohort | 46 | case:29.4(27.4–31.3) control:29.3(27–31.7) | case:1285(800–1945) control:1310(665–1980) | Medical records; cranial ultrasound within 6–8 weeks after birth | No representativeness of the exposed cohort, follow-up was not long enough for outcome;NOS:7 | |
| Kubota 2001 [7] | Japan | Case-control | 51 | 29.8±2.7 | case:1399±505 control:1410±479 | Medical records; cranial ultrasound within 4 weeks after birth and once per week thereafter | No representativeness of the cases, no report of non-response rate;NOS:7 | |
| Resch 2000 [23] | Austria | Case-control | 3187 | 31±2.5(26–35) | case:1511±456 control:1499±446 | Medical records; cranial ultrasound at days 1, 3, and 5 of life and repeated weekly until diagnosis | No representativeness of the cases, no report of non-response rate;NOS:7 | |
| Spinillo 1998 [24] | Italy | Retrospective cohort | 349 | case:29.4±2.2 control:30.5±2.5 | case:1267±378 control:1452±445 | Medical records; cranial ultrasound within 2 weeks after birth | No representativeness of the exposed cohort;NOS:8 | |
| Perlman 1996 [25] | United States | Retrospective cohort | 709 | case:29.4±1.5 control:26.6±1.8 | case:1285±301 control:904±248 | Medical records; cranial ultrasound within 1 week after birth | No representativeness of the exposed cohort;NOS:8 | |
Abbreviations: GA (w), gestational age (weeks); BW (g), birth weight (grams); NOS, score of Newcastle-Ottawa scale.