Deaths related to intrapartum asphyxia

Fetal death in labour is extremely rare. Although the total fetal death (stillbirth) rate has more than halved over the past 30 years, and is now about 5.5 per 1000 total births, the rate of intrapartum fetal death in babies above 1500 g is only 0.3 per 1000 total births.¹,² Hypoxia is thought to be a factor in 90% of intrapartum deaths,² and much of the reduction has been credited to continuous fetal heart rate monitoring, introduced into clinical practice about 30 years ago. Use of continuous fetal heart rate monitoring was soon found to be associated with significant falls in perinatal mortality,³,⁴ and further evidence for an inverse association between the level of perinatal technology and the incidence of intrapartum fetal death came from the 1980 American national fetal mortality survey.⁵ Interestingly, the Dublin randomised controlled trial of fetal heart rate monitoring in labour found no differences in intrapartum stillbirth rates, or long term outcome, between groups monitored by intermittent auscultation and by continuous fetal heart rate monitoring.⁶ However, this study was performed against a background rate of 0.3-0.4 intrapartum fetal deaths per 1000, and this very low rate remains the present challenge to attempts to reduce it still further.

The confidential inquiry into stillbirths and deaths in infancy focuses on preventable factors in intrapartum related perinatal deaths. The fetuses who die are more likely than controls to have had placental abruption, cord prolapse, fetal distress, or an unhealthy placenta.⁷ The inquiry found that 75% of intrapartum related deaths showed examples of suboptimal intrapartum care which might have contributed to the outcome. Over 90% of these examples related to failure to recognise a problem, act appropriately, or communicate adequately. A long delay between the onset of fetal compromise and delivery has been highlighted as a major contribution to intrapartum fetal deaths.⁸

Intrapartum asphyxia accounts for both fetal deaths in labour and neonatal deaths. Analysis by cause was recommended by Wigglesworth in 1980⁹ and is used by the confidential inquiry. It was also the approach taken by Stewart and colleagues in their study of the frequency of asphyxial deaths according to time of birth, published on page 657.¹⁰ They looked at 33 intrapartum deaths (rate 0.31 per 1000 registrable births), 42 neontal deaths in the first week (0.39 per 1000), and 4 deaths at days 8-28 (0.04 per 1000) identified from the confidential inquiry in Wales in 1993-5. They limited their study to babies born with a birth weight of 1500 g or more and found that twice as many of the babies who died from intrapartum asphyxia had been born between 9 pm and 9 am; the relative risk was similarly doubled for births in July and August. They did not, however, find higher rates of total perinatal mortality at the weekend, as found in a previous study.¹¹

The study of Stewart et al raises an intriguing question. Is staff performance at night, and in July and August, sufficiently different to account for this twofold increase in asphyxia related mortality, or does fetal asphyxia during labour at night present differently? Spontaneous labour is known to occur more often at night, and such labours may be associated with a different presentation of chronic fetal compromise from the iatrogenic compromise more likely to be associated with induction of labour.¹² Although it is tempting to conclude that night staff may be less able to identify fetal compromise, further study is essential before this conclusion is accepted. In 1970 data from the collaborative perinatal study in America showed that 57% of term stillbirths were unexplained.¹³ UK data from the confidential inquiry show that 51% of intrapartum deaths remain unexplained.¹ This figure has not changed in over 25 years, despite a halving of perinatal mortality.

A deep rooted ambivalence exists among professionals about the use of continuous fetal heart rate monitoring in labour. Much is expected of this simple tool, and much difficulty results from its use. The recent confidential inquiry report shows that most adverse comments about continuous fetal heart rate records in labour related to poor education.¹ If continuous fetal heart rate monitoring is to stay¹⁴ there is a clear need to achieve an improved understanding of the physiological basis for control of the fetal heart rate.¹⁵ Only with better knowledge and understanding of how the fetal heart provides information about fetal oxygenation can staff hope to address the epidemiological question of whether serious intrapartum asphyxia presents in a way that is less obviously recognised at night.

Paper p 657