Continued reduction in the incidence of birth trauma and birth asphyxia related to instrumental deliveries after the study period: was this the Hawthorne effect?
BACKGROUND
The incidence of birth trauma and birth asphyxia related to instrumental deliveries in our obstetric unit was high (2.8%) in 1998-1999. A study was performed in 2000 to identify the risk factors. Unexpectedly, the incidence (0.6%) was reduced significantly during the study period. We attributed this phenomenon to the famous Hawthorne effect (tendency to improve performance because of awareness of being studied).


OBJECTIVE
The objectives were to study whether there is a continued reduction in the incidence of birth trauma and birth asphyxia related to instrumental deliveries in the post-study period (2001-2003) and to investigate the presence of underlying confounding factors apart from the Hawthorne effect.


METHODS
To compare the hospital obstetric statistics among the pre-study period (1998-1999), the study period (2000) and the post-study period (2001-2003), in particular the incidence of birth trauma and birth asphyxia related to instrumental deliveries, the instrumental delivery rate, the overall Caesarean section rate, the Caesarean section rate for no progress of labour, the incidence of failed instrumental delivery, the incidence of attempted instrumental delivery in the operating theatre, and incidence of direct second-stage Caesarean sections.


RESULTS
The incidence of birth trauma and birth asphyxia related to instrumental deliveries (0.6%) during the study period (2000) was significantly lower than that (2.8%) during the pre-study period (1998-1999; RR 0.27, 95% CI 0.11-0.70). This phenomenon continued into the post-study period (2001-2003) when the incidence of 1.0% was similarly lower than that in the pre-study period (RR 0.35, 95% CI 0.20-0.64). The instrumental delivery rate decreased further in the post-study period (13.5%) compared with those in the study (16.6%) and pre-study (19.5%) periods (RR 0.81, 95% CI 0.75-0.89 and RR 0.69, 95% CI 0.65-0.74, respectively). There was a marked increase in the direct second-stage Caesarean section rate in the post-study period (7.1%) compared to those in the study (0.4%) and pre-study (0.7%) periods (RR 15.9, 95% CI 5.05-49.73 and RR 9.77, 95% CI 5.28-18.08, respectively).


CONCLUSIONS
A change in obstetric practice was identified that may explain the continued reduction in the incidence of birth trauma and birth asphyxia related to instrumental deliveries in the post-study period.
Department of Obstetrics and Gynaecology, Queen Mary Hospital, University of Hong Kong, HKSAR, China. leungwc65@hotmail.com
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D001238:Asphyxia Neonatorum / Q000453:epidemiology* / Q000517:prevention & control; D001720:Birth Injuries / Q000453:epidemiology* / Q000517:prevention & control; D002681:China / Q000453:epidemiology; D036861:Delivery, Obstetric / Q000706:statistics & numerical data; D015987:Effect Modifier, Epidemiologic; D005113:Extraction, Obstetrical / Q000009:adverse effects* / Q000706:statistics & numerical data; D005260:Female; D006785:Hospitals, University / Q000706:statistics & numerical data*; D006801:Humans; D007231:Infant, Newborn; D009017:Morbidity; D017410:Practice Guidelines as Topic; D011247:Pregnancy; D012307:Risk Factors