Authors’ replyBMJ 2010; 341 doi: https://doi.org/10.1136/bmj.c7023 (Published 07 December 2010) Cite this as: BMJ 2010;341:c7023
- Annemieke C C Evers, PhD student, resident in gynaecology1,
- Hens A A Brouwers, neonatologist1,
- Chantal W P M Hukkelhoven, epidemiologist2,
- Peter G J Nikkels, pathologist1,
- Janine Boon, gynaecologist3,
- Anneke van Egmond-Linden, gynaecologist4,
- Jacqueline Hillegersberg, paediatrician5,
- Yvette S Snuif, gynaecologist6,
- Sietske Sterken-Hooisma, midwife secondary care7,
- Hein W Bruinse, professor of obstetrics1,
- Anneke Kwee, gynaecologist1
- 1University Medical Center Utrecht, 3584 EA Utrecht, Netherlands
- 2Netherlands Perinatal Registry, Utrecht, Netherlands
- 3Department of Obstetrics and Gynaecology, Diakonessenhospital, Utrecht, Netherlands
- 4Department of Obstetrics and Gynaecology, Zuwe Hofpoort Hospital, Woerden, Netherlands
- 5Department of Pediatrics, St Antonius Hospital, Nieuwegein, Netherlands
- 6Department of Obstetrics and Gynaecology, Admiraal de Ruyter Hospital, Goes, Netherlands,
- 7Department of Obstetrics and Gynaecology, Meander Medical Center, Amersfoort, Netherlands
De Jonge and colleagues and Pop and Wijnen commented on the nomenclature of our study.1 2 We performed a cohort study, including cases in a prospective manner. Thus important problems associated with retrospective data collection—such as dependence of the investigator on the availability and accuracy of medical case records and classification bias of the cases—are prevented. The population at risk was estimated retrospectively using aggregated, prospectively collected data from the national perinatal register. We emphasised these limitations in our paper.
De Jonge and colleagues are concerned that mortality in midwifery practices may be artificially inflated. To show that our findings were not caused by under-reporting of normal births we did artificially increase the denominator by 10% in the paper without any difference in model outcome. If we increase the denominator by another 5%, accounting for the possibility that we have missed births from the periphery of our catchment area, the findings still remain robust.
De Jonge and colleagues and Pop and Wijnen note the discrepancy between our results and those of previous studies.3 4 Notwithstanding the differences in study design, our perinatal mortality among term infants without congenital anomalies, 2.6 per 1000, is similar to that in large nationwide studies.5 6 Classification problems in databases might explain the differences.
To our knowledge, ours is the only study in the Netherlands showing a higher risk of delivery related perinatal mortality among women with the intention to deliver in primary care compared with women who start delivery in secondary care. Given the limitations of the study, we agree that our study design cannot show a causal association between the results and (specific parts of) the obstetric care system. We emphasise that we only philosophised about possible explanations and solutions in the discussion and hope that our paper will stimulate further discussion that may lead to improvement in outcome for newborn infants.
Cite this as: BMJ 2010;341:c7023
Competing interests: None declared.