1. UKK Institute for Health Promotion Research, 33501 Tampere, Finland
2. Department of Children and Families, National Health and Welfare Institute, 00271 Helsinki, Finland
3. R. Samuel McLaughlin Foundation-Exercise and Pregnancy Lab, 3-M Centre, The University of Western Ontario, London, ON, Canada N6A 3K7
4. Georgetown University, Research Building, Room E407, 3970 Reservoir Road, NW, Washington, DC 20057, USA