Jones Myfanwy Lloyd, Wray Julie, Wight Jeremy, Chilcott Jim, Forman Katie, Tappenden Paul, Beverley Catherine
School of Health and Related Research (ScHARR), University of Sheffield, UK.
BJOG. 2004 Sep;111(9):892-902. doi: 10.1111/j.1471-0528.2004.00243.x.