Prospective risk of stillbirthBMJ 2000; 320 doi: https://doi.org/10.1136/bmj.320.7232.444/a (Published 12 February 2000) Cite this as: BMJ 2000;320:444
Study's results are flawed by reliance on cumulative prospective risk
- Lisa Hilder, lecturer,
- Kate Costeloe, professor,
- Baskaran Thilaganathan, director (firstname.lastname@example.org)
- Department of Environmental and Preventative Medicine, Wolfson Institute of Preventive Medicine, London EC1M 6BQ
- Academic Department of Child Health, St. Bartholomew's and the Royal London School of Medicine and Dentistry, London E1 4NS
- Fetal Medicine Unit, St George's Hospital Medical School, London SW17 0RE
- Unité de Développement en Obstétrique, Hôpitaux Universitaires de Genève, CH-1211 Geneva, Switzerland
- Department of Primary Health Care, Institute of Health Sciences, Oxford OX3 7LF
- Nuffield Department of Obstetrics and Gynaecology, John Radcliffe Hospital, Oxford OX3 9DU
- Department of Maternal and Fetal Medicine, Institute of Obstetrics and Gynaecology, Imperial College School of Medicine, Queen Charlotte's and Chelsea Hospital, London W6 0XG
EDITOR—In their study on the prospective risk of unexplained stillbirth in singleton pregnancies at term Cotzias et al performed a secondary analysis1 of data that we published.2 The proposed rationale for this mathematical exercise was that no published data provide accurate gestation-specific risks of stillbirth at term. In fact, our publication evaluates risks of stillbirth and neonatal and infant mortality throughout pregnancy.2
The original data for the North East Thames region, with the addition of births for 1992, were used to inform the confidential inquiry into stillbirths and deaths in infancy (CESDI) concerning antepartum stillbirths (L Hilder and N Datta, unpublished data). When both fetal and neonatal causes cited on stillbirth registrations were used the proportion of stillbirths that are unexplained increased from 0.1392 at 37 weeks to 0.5000 at 43 weeks. Even if stillbirth is explainable it is not necessarily preventable and is inevitably unexpected. We acknowledge that when doctors deal with parents who have had a recent stillbirth, information on aetiology is invaluable. We continue to believe, however, that when prospective risks are being estimated for clinical purposes all stillbirths should be included.
The results presented by the authors are critically flawed by the reliance on cumulative prospective risk of stillbirth. The authors total the number of stillbirths in the remaining weeks of pregnancy in order to estimate the prospective risk of stillbirth at a specific week of gestation. This methodology produces clinically implausible results, explaining the authors' paradoxical conclusion that the risk of stillbirth at 38 weeks is greater than that at 42 weeks. If this was taken to absurdity their prospective risk of stillbirth at 24 weeks would be 1 in 330 while that at 43 weeks would be 1 in 633.
We analysed data from 158 945 singleton pregnancies in the North …