Several factors predisposing to increased mortality at night were not excluded

EDITOR—Heller et al's unstated premise that the incidence of perinatal death due to intrapartum asphyxia in low risk pregnancies may serve as a sensitive measure of the quality of peripartum care delivered is appealing. 1 2 But their proposition that the observed higher nocturnal perinatal mortality in their selected population arose because of substandard care was not justified.

Firstly, the authors did not do a comprehensive interrogation of index case records. The Confidential Enquiry into Stillbirths and Deaths in Infancy adopts the gold standard method of a multidisciplinary scrutiny of records to ensure accurate diagnosis and quantify substandard care.

Secondly, imprecise selection criteria meant that the sample population was heterogeneous in terms of pregnancy risk and method of delivery. Further bias arose because Heller et al's early neonatal death rate (0.15/1000 births selected) represented only a small fraction of the unstated overall early neonatal death rate (3.1/1000 live births found in a similar population by the Confidential Enquiry into Stillbirths and Deaths in Infancy3).

Thirdly, criteria required before perinatal asphyxia is diagnosed were not adopted.4 Deaths classified as asphyxia related that occurred as a result of hypoxia during labour do not necessarily …