Australia's mothers and babies

This section examines perinatal deaths that occurred in singleton pregnancies, where the baby did not have a major congenital anomaly causing death and where the pregnancy ended at or after 36 weeks of gestation. For the purposes of this report, such babies are called ‘near-term normally-formed singleton babies’.

These babies have the lowest incidence of known risk factors for perinatal death, and so any deaths occurring in this group of babies are considered to be unexpected. When considering prevention of perinatal deaths, review of perinatal deaths in this group of babies is likely to provide insights to inform policy and practice in maternity and neonatal care (Draper et al. 2015, 2017; RCOG 2017).

In 2020–2021, near-term normally-formed singleton babies accounted for a large proportion (571,160, 93%) of all babies born and a small proportion (720, 12%) of perinatal deaths. Perinatal deaths among this group:

• occurred at a low rate compared with all babies born in Australia, with 1.3 deaths per 1,000 births in 2020–2021 compared with 9.8 deaths per 1,000 births among all babies in 2020–2021
• were more commonly a stillbirth (563, 78%) than a neonatal death (157, 22%)
• occurred at the highest rate at 36 weeks of gestation (7.5 perinatal deaths per 1,000 births) and among babies with a birthweight less than the 10^th percentile (2.6 perinatal deaths per 1,000 births).

Trends in perinatal mortality rates

The rate of perinatal death among near-term normally-formed singleton babies has remained relatively unchanged since 2013, varying between 1.2 and 1.5 deaths per 1,000 births (Figure 1).

Maternal characteristics

The overall rate of perinatal mortality among near-term normally-formed singleton babies in 2020–2021 was 1.3 deaths per 1,000 births. Perinatal mortality rates were higher among babies born to:

• women with pre-existing diabetes mellitus (5.4 deaths per 1,000 births)
• women who accessed 2 or fewer antenatal visits (4.4 perinatal deaths per 1,000 births)
• women who were aged under 20 (2.9 deaths per 1,000 births)
• women who have had four or more previous births (2.8 deaths per 1,000 births)
• women who reported smoking throughout pregnancy (2.7 deaths per 1,000 births)
• women living in the most disadvantaged areas of Australia (1.7 deaths per 1,000 births for SEIFA quintile 1)
• women who lived in Remote and very remote areas (1.7 deaths per 1,000 births)
• women classed as obese (BMI of 30 or more; 1.6 deaths per 1,000 births).

Many of these associations are also observed for all perinatal deaths in Australia (see Stillbirths and neonatal deaths: Maternal characteristics for more details).

Detailed data on perinatal mortality rates by selected maternal characteristics can be explored in the interactive data visualisation below (Figure 2), with data also presented in Table 16 of the supplementary data tables (Data tables: National Perinatal Mortality Data Collection annual update 2021).

Figure 2: Perinatal mortality rates among near-term normally-formed singleton babies, by selected maternal characteristic, 2020–2021

Baby characteristics

The length of pregnancy and the weight of the baby are often related. Using birthweight for gestational age allows for differences in a baby's growth and maturity to be considered in relation to health outcomes. For example, a baby may be small because it has been born early, or it may be small for its gestational age when compared with other babies of the same age. It might be small due to genetic factors, or because of a growth restriction within the uterus. Babies are considered small for gestational age when their birthweight is below the 10^th percentile for their gestational age and sex.

In 2020–2021, the overall rate of perinatal deaths in near-term normally formed babies was 1.3 deaths per 1,000 births. Perinatal mortality rates were highest for:

• babies born at 36 weeks’ gestation (7.5 deaths per 1,000 births)
• babies born with a birthweight less than 2,500 grams (5.6 deaths per 1,000 births)
• babies who were small for gestational age (2.6 deaths per 1,000 births), especially for those babies whose birthweight was less than the 3rd percentile for their gestational age (4.0 deaths per 1,000 births).

Detailed data on perinatal mortality rates by birthweight, gestational age and sex can be explored in the interactive data visualisation below (Figure 3), with data also presented in Table 17 of the supplementary data tables (Data tables: National Perinatal Mortality Data Collection annual update 2021).

Figure 3: Perinatal mortality rates among near-term normally-formed singleton babies, by selected baby characteristic, 2020–2021

Timing of perinatal death

Among near-term normally-formed singleton babies, nearly three-quarters (72%) of perinatal deaths occurred prior to the onset of labour (antepartum stillbirth) (Figure 4).

Causes of death

The most common causes of perinatal death for near-term normally-formed singleton babies, using the PSANZ-PDC classification, were stillbirths where no cause could be found (‘unexplained antepartum death’) (22%) and deaths where the placenta wasn’t functioning well (‘placental dysfunction or causative placental pathology’) (17%) (Figure 5).

The most common causes of stillbirth and neonatal death were different from each other. For stillbirths, the most common cause was ‘unexplained antepartum death’ (29%), followed by ‘placental dysfunction or causative placental pathology’ (20%).

For neonatal deaths, the most common cause was not receiving enough oxygen from the placenta (‘hypoxic peripartum death’, 38%), followed by deaths which could not be explained by a problem in the pregnancy (‘neonatal death without obstetric antecedent’, 22%).

Causes of perinatal deaths among near-term normally-formed singleton babies also varied by birthweight percentile. Deaths among babies considered small for their gestational age (weighing less than the 10^th percentile), which accounted for 134 or 19% of perinatal deaths, were most commonly due to ‘placental dysfunction or causative placental pathology’ (38 perinatal deaths), followed by ‘unexplained antepartum death’ (28 perinatal deaths).

Babies considered large for their gestational age (weighing greater than the 90^th percentile) most commonly died as a result of ‘unexplained antepartum death’ (18 perinatal deaths), followed by ‘maternal conditions’ (16 perinatal deaths), which includes medical conditions (for example, diabetes), surgical conditions (for example, appendicitis) and injuries, as well as complications or treatment of that condition.

The PSANZ-NDC classification system is applied only to neonatal deaths, to identify the single most significant condition present in the neonatal period that caused the baby’s death. For the majority of neonatal deaths among near-term normally-formed singleton babies, the single most significant condition that caused the baby’s death was brain damage due to oxygen deprivation or bleeding in the brain (‘neurological conditions’, 54%) (Figure 6).

Detailed data on the causes of perinatal deaths among near-term normally-formed singleton babies in 2020–2021 is presented in Table 18 of the supplementary data tables (Data tables: National Perinatal Mortality Data Collection annual update 2021).

Autopsy following perinatal death

This section presents data on autopsy, identified by PSANZ as a core investigation (test) to be undertaken following all perinatal deaths (Flenady et al. 2020).

Testing such as autopsy is of particular importance in seeking the underlying causes of death in near-term normally-formed singleton babies. A greater proportion of these babies have causes of death that are unknown (‘unexplained antepartum death’), not well understood (‘hypoxic peripartum death’), or cannot be explained by a problem occurring in the pregnancy (‘neonatal death without obstetric antecedent’). Combined, these 3 causes of death accounted for 40% of deaths in near-term normally-formed singleton babies. This is a higher incidence than for all perinatal deaths, where these causes of death accounted for 14% of deaths.

Where autopsy status was known, autopsy was performed more frequently among near-term normally-formed singleton babies (57%) than for perinatal deaths occurring across all babies (41%). For near-term normally-formed singleton babies, the proportion of autopsy was similar across stillbirths (57% of stillbirths) and neonatal deaths (59% of neonatal deaths).

The frequency at which autopsy was conducted varied by timing of perinatal death, with the highest proportion being performed in very early (less than 24 hours) neonatal deaths (72%).

The frequency of autopsy also varied by cause of death, with 77% of neonatal deaths with ‘no obstetric antecedent’ undergoing an autopsy compared with 30% of deaths due to ‘antepartum haemorrhage’. Autopsy investigation was conducted in less than half of stillbirths classified as ‘unexplained antepartum deaths’ (47%).

Detailed data on the investigation of perinatal deaths among near-term normally-formed singleton babies in 2020–2021 can be explored in the interactive data visualisation below (Figure 7), with data also presented in Table 18 of the supplementary data tables (Data tables: National Perinatal Mortality Data Collection annual update 2021).

Figure 7: Proportion of perinatal deaths among near-term normally-formed singleton babies where autopsy was performed, 2020–2021