1. Department of Growth and Reproduction (C.P.H., A.M., M.G.M., J.T., C.W.-V., A.J., K.M.M.), DK-2100 Copenhagen, Denmark;
2. Department of Radiology, (E.F.), DK-2100 Copenhagen, Denmark;
3. Department of Fetal Medicine and Ultrasound (V.B., K.S., L.N.J.),Rigshospitalet Faculty of Health and Medical Sciences, University of Copenhagen, DK-2100 Copenhagen, Denmark;
4. Medical Research Council Centre for Reproductive Health (R.A.A.), University of Edinburgh, Edinburgh EH16 4TJ, United Kingdom