Explanatory notes

​​​​​​​​​​​​​​​​​​Aborigi​nal babies

The Aboriginal status of babies is assigned according to how the mother identified her baby or herself during the birth admission. Babies born to Aboriginal mothers and babies identified as Aboriginal by their mothers are included as Aboriginal babies in this data.

Aboriginal and Torres Strait Islander people are referred to as Aboriginal people in recognition that Aboriginal people are the original inhabitants of NSW.​

Aboriginal ​mothers

​​Women who identify themselves as Aboriginal.​

Aboriginal and Torres Strait Islander people are referred to as Aboriginal people in recognition that Aboriginal people are the original inhabitants of NSW.

​​​Apgar score

A numerical scoring system routinely administered 1 and 5 minutes after birth to evaluate the condition of the baby. The score ranges from 0 to 10. It takes account of five physical signs: heart rate, respiration, muscle tone, reflexes, and colour. Each is assigned a component score of 0, 1 or 2. A 5-minute Apgar score of 7 or above is considered normal.

Augmentation

Artificial rupture of the membranes or use of oxytocic drugs after spontaneous onset of labour.

Birthweight

The newborn baby’s first bare weight in grams.

  • Low birthweight: birthweight less than 2,500 grams.
  • Very low birthweight: birthweight less than 1,500 grams.
  • Extremely low birthweight: birthweight less than 1,000 grams.

Body Mass Index (BMI) and weight ​categories

Weight categories are assigned according to body mass index (BMI). BMI is a commonly used measure for monitoring rates of overweight and obesity in populations. It is calculated as the ratio of a person’s weight in kilograms divided by height in metres squared. In the NSW Perinatal Data Collection, weight is usually reported at the first comprehensive antenatal assessment; however, self-reported weight around the time of conception is acceptable if a measured weight is not available. The Perinatal Data Collection does not include information on whether the reported weight was measured or self-reported.

BMI classifications categorise adults as underweight (BMI below 18.5), healthy weight (BMI 18.5–24.9), overweight (BMI 25.0–29.9) and obese (BMI 30 or above).

Values of height, weight and BMI were excluded if they were outside the 1st and 99th percentile of the United States Centers for Disease Control Growth Charts for girls.1 For mothers aged over 18 years, the BMI score is classified using World Health Organization criteria.2 For mothers aged less than 18 years, modified BMI thresholds are used, as described by Cole et al.3,4 For more information see HealthStats NSW – Estimates of maternal overweight and obesity based on the NSW Perinatal Data Collection.

Breastfeeding

Infant feeding is reported via three tick-box categories: breastfeeding, expressed breast milk, and infant formula. More than one type of feeding may be reported by ticking multiple boxes. In this report, infant feeding is classified into three categories: 

  • ​Full breastfeeding, which includes babies who were reported to be breastfed or to be receiving expressed breast milk.
  • Partial breastfeeding, which includes babies who were reported to be receiving breast milk and infant formula.
  • Infant formula only (no breastfeeding).

Caesarean section

Birth of the fetus through an abdominal incision. 

  • ​​​​Elective caesarean section: a caesarean section (planned or unplanned) performed before the onset of labour. 
  • Emergency caesarean section: a caesarean section performed after the onset of labour, whether or not the onset of labour was spontaneous.

Confinement

Refers to a woman having given birth. In a multiple pregnancy, one confinement will result in more than one birth.

Epidural

Injection of analgesic agent outside the dura mater which covers the spinal canal; includes lumbar, spinal, and epidural anaesthetics.​

Episiotomy

An incision of the perineum and vaginal wall to enlarge the birth passage.

Gestational age

The duration of pregnancy in completed weeks from the first day of the last normal menstrual period. Where accurate information on the date of the last menstrual period is not available or the menstrual period is not regular, a clinical estimate of gestational age may be obtained from other methods such as ultrasound during the first half of pregnancy. The “best estimate” is used in this report.​

Induction of labour

  • Oxytocics–prostaglandins: medical initiation of labour by the use of oxytocic agents, prostaglandins, or their derivatives (oral, intravaginal or intravenous).
  • ARM only: the surgical initiation of labour by artificial rupture of membranes.
  • Oxytocics–prostaglandins and ARM: both medical and surgical induction as defined above (combined medical and surgical induction).​

​Labour

The category labour–spontaneous with oxytocics–prostaglandins was used where labour was augmented with artificial rupture of membranes as well as oxytocics or prostaglandins.​

Live birth

The complete expulsion or extraction from its mother of a baby who, after being born, breathes or shows any evidence of life such as a heartbeat.

Maternity service capability levels

The maternity service capability levels for 2024 have been applied to the data in this report. These are explained in the NSW Health Guideline Maternity and Neonatal Service Capability (GL2022_022),​​ w​​hich guides NSW local health districts in determining the service capability of their maternity and neonatal services. 

​For further information on role delineation levels for individual sites, please contact the relevant local health district.​​

Parity

The total number of live births and stillbirths of the mother before the pregnancy or birth under consideration.

Perinatal death

Perinatal deaths include neonatal deaths and stillbirths.​​
​
  • Neonatal death: Neonatal deaths reported to the NSW Perinatal Data Collection include deaths that occurred before the baby was discharged or transferred from the birth hospital. Neonatal deaths reported to the NSW Perinatal Death Review Data Collection include deaths of babies who were born and died in NSW within 28 days of birth, including babies who died after discharge or transfer from the hospital of birth.
  • Stillborn baby: A stillborn baby means a baby that exhibits no sign of respiration or heartbeat, or other sign of life, after birth and that: ​​​​​(​a) is of at least 20 weeks gestation, or ​(b) if it cannot be reliably established whether the period of gestation is more or less than 20 weeks, has a body mass of at least 400 grams at birth.

This report includes stillbirths and neonatal deaths within the scope of the NSW Perinatal Data Collection (which includes births from 20 weeks gestation or babies of at least 400 grams birthweight), which includes some terminations of pregnancy.​

Perinatal mortality rate

The number of perinatal deaths (stillbirths and neonatal deaths) per 1,000 total births in a year (live births and stillbirths combined).

With the exception of reporting in the Maternal and perinatal deaths section, perinatal deaths in this report include deaths reported to the NSW Perinatal Data Collection only. As the Perinatal Data Collection record is completed at discharge or transfer of the baby, deaths occurring after this time are not reported to the NSW Perinatal Data Collection. Birth and perinatal death registration data held by the Australian Bureau of Statistics give the most complete overall ascertainment of perinatal deaths for calculation of rates.

Perineal status

  • 1st degree tear: a perineal graze/laceration or tear involving the fourchette, hymen, labia, skin, vagina, or vulva.
  • 2nd degree tear: a perineal laceration or tear involving the pelvic floor, perineal muscles, or vaginal muscles.
  • 3rd degree tear: a perineal laceration or tear involving the anal sphincter or rectovaginal septum​.
  • 4th degree tear: a 3rd degree perineal laceration or tear which also involves the anal mucosa or rectal mucosa​.

Place of residence of mother

The mother’s usual residence was the basis for coding to statistical areas of residence and NSW local health districts.

Plurality

The number of fetuses in utero at 20 weeks gestation that are subsequently born separately. On this basis a pregnancy may be classified as single or multiple.

Premature baby

A baby born before 37 completed weeks gestation.

Small for gestational age

Small for gestational age is defined as a birthweight below the 10th percentile for liveborn singleton babies of the same gestational age and sex as defined by the Australian Institute of Health and Welfare's birthweight percentile table.5​​ This data is only available for gestational ages between 20 and 44 weeks and does not include babies with an indeterminate sex.​

Term baby

A baby born at 37 or more completed weeks gestation.

Type of birth

The “vaginal breech” category covers all forms of vaginal breech birth, including forceps to the after-coming head.​​

​ References

  1. Centers for Disease Control and Prevention. Percentile Data Files with LMS Values. Accessed 22 November 2025​.
  2. World Health Organization. Obesity: Preventing and Managing the Global Epidemic 2000, WHO Technical Report Series 894​. World Health Organization. Accessed 22 November 2025.
  3. Cole TJ, Flegal KM, Nicholls D, Jackson AA. Body mass index cut offs to define thinness in children and adolescents: international survey. BMJ 2007; 335(7612): 194. Accessed 22 November 2025.
  4. Cole TJ, Bellizi MC, Flegal KM, Dietz WH. Establishing a standard definition for child overweight and obesity worldwide: international survey. BMJ​ 2000; 320(7244): 1240-3. Accessed 22 November 2025.
  5. ​​Australian Institute of Health and Welfare. Australia's mothers and babies.​ ​​National Perinatal Data Collection annual update 2023, Table 7.2: Australian birthweight percentiles for liveborn singleton babies, by sex and gestational age, 2013 to 2022​​. Accessed 22 November 2025​. ​​​​​​
Current as at: Monday 18 May 2026