Table 1.
Descriptive statistics and regression coefficients for the difference in birth size of dizygotic twin boys and girls according to the sex of their co-twin (reference group same-sex dizygotic twins).
| SS | OS | B | p-value | CIs | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| n | Mean | SD | n | Mean | SD | |||||
| Boys | ||||||||||
| Birth weight (kg) | 17584 | 2.578 | 0.57 | 16417 | 2.608 | 0.56 | 0.031 | <0.001 | 0.018 | 0.045 |
| Birth length (cm) | 8702 | 47.42 | 3.28 | 8170 | 47.60 | 3.30 | 0.160 | 0.006 | 0.045 | 0.274 |
| PI at birth (kg/m3) | 8702 | 24.41 | 3.12 | 8170 | 24.44 | 3.13 | 0.021 | 0.691 | −0.083 | 0.125 |
| Girls | ||||||||||
| Birth weight (kg) | 17432 | 2.495 | 0.54 | 16417 | 2.497 | 0.54 | 0.005 | 0.466 | −0.008 | 0.018 |
| Birth length (cm) | 8128 | 46.94 | 3.14 | 8170 | 46.85 | 3.28 | −0.089 | 0.125 | −0.202 | 0.025 |
| PI at birth (kg/m3) | 8128 | 24.45 | 3.21 | 8170 | 24.46 | 3.18 | 0.005 | 0.933 | −0.103 | 0.113 |
Participating twin cohorts in this study: Australian Twin Registry, Carolina African American Twin Study of Aging, Child and Adolescent Twin Study in Sweden, East Flanders Prospective Twin Survey, Finntwin12, Finntwin16, Gemini Study, Guinea-Bissau Twin Study, Hungarian Twin Registry, Italian Twin Registry, Japanese Twin Cohort, Longitudinal Israeli Study of Twins, Michigan Twins Study, Minnesota Twin Registry, Mongolian Twin Registry, Peri/Postnatal Epigenetic Twins Study, Qingdao Twin Registry of Children, Quebec Newborn Twin Study, Twins Early Developmental Study, West Japan Twins and Higher Order Multiple Births Registry and Young Netherlands Twin Registry.