Table 2 Description of the articles included in meta-analyses. All study designs are cross-sectional, and all studies used singleton standards to classify low birth weight
| Study ID (author, year) | Country | Number of participants | Enrollment period | Outcome | Maternal age | Gestational age |
Zygosity (MZ/DZ) |
Sex (MM/MF/FF) |
|---|---|---|---|---|---|---|---|---|
| Ortqvist 2009 [11] | Sweden | 10918 | 2004-2007 | Asthma |
≤ 19: 18.4% 20-24: 16.1% 25-29: 13.9% 30-34: 13.9% ≥ 35: 11.8% |
≤31: 24.8% 32-34: 18.1% 35-36: 14.1% 37-38: 11.7% 39-40: 10.7% ≥ 41: 12.9% |
MZ: 13.4% DZ: 28.4%: Unknown: 11.7% | - |
| Rasanen 2000 [26] | Finland | 4502 | 1975-1979 | Asthma |
< 25: 31.4% 25-30: 38.8% > 30: 29.8% |
< 33: 7.1% 33-36: 29.0% 37-40: 60.6% > 40: 3.3% | - | - |
| Villamor 2009 [28] | Sweden | 32580 | 1926-1958 | Asthma |
< 20: 2.7% 20-24: 17.0% 25-29: 29.9% 30-34: 27.4% ≥ 35: 22.9% Missing: 0.1% |
31-34: 12.9% 35-36: 20.0% 37-41: 58.7% 42-45: 3.5% Missing: 4.8% | - |
MM: 47.2% FF: 52.8% |
| Gardner 1995 [25] | USA | 1079 | 1959-1966 | Cerebral palsy | - | - |
MZ: 31.9% DZ: 58.6% Unknown: 9.4% |
Concordant: 63.9% Discordant: 36.1% |
| Suvanand 1997 [27] | India | 250 | 1993-1994 | Cerebral palsy | - | - | - | - |