What are the legal viable age and weight criteria for a neonate?

Legal Viable Age and Weight Criteria for Neonates

Live birth is legally defined as the complete expulsion or extraction of a product of fertilization after 20 completed weeks of gestational age that shows any evidence of life (breathing, heartbeat, umbilical cord pulsation, or voluntary muscle movement), or alternatively, a birth weight of 350 g or more can be used if gestational age is unknown. 1

Gestational Age Criteria

• The threshold for legal viability is 20 completed weeks of gestational age, which represents the standard international definition for distinguishing live birth from pregnancy loss 1
• Gestational age is calculated by the best obstetric estimate using early ultrasound, last menstrual period date, and/or perinatal details 1
• For assisted reproductive techniques, gestational age is calculated by adding 14 days to the number of completed weeks since fertilization 1

Birth Weight Criteria

• When gestational age is unknown, a birth weight of 350 g or more serves as the alternative criterion for defining live birth 1
• Birth weight should be collected within 24 hours of birth using a calibrated electronic scale with 10-g resolution 1
• This weight-based criterion provides a practical alternative when accurate gestational age dating is unavailable 1

Evidence of Life Requirements

Any of the following signs constitute evidence of life for legal viability determination 1:

• Breathing or respiratory effort
• Heartbeat detected
• Umbilical cord pulsation
• Definite movement of voluntary muscles

These criteria apply irrespective of whether the umbilical cord has been cut or the placenta is attached 1

Clinical Context for Periviable Births

• Between 22 weeks 0 days and 25 weeks 6 days represents the periviable period, which accounts for 0.2% of all live births and is a major source of neonatal morbidity and mortality 2
• Active treatment decisions during this period are challenging, with overall active treatment rates of approximately 52% for periviable neonates 2
• Neonatal survival increases dramatically with gestational age: 13% at 24 weeks, 43% at 25 weeks, and 58-76% at 26 weeks 3

Important Clinical Distinctions

• Neonatal mortality is defined as death of a live-born baby within 28 days of birth, which can be subdivided into early neonatal mortality (first 7 days) and late neonatal mortality (8-28 days) 1
• Stillbirth refers to fetal death occurring after 20 weeks gestation but before complete expulsion or extraction 1
• Coordination of care between maternal-fetal medicine and neonatology services is necessary for deliveries before 26 weeks or at 500g 3

Common Pitfalls

• Do not confuse the legal definition of live birth (≥20 weeks or ≥350g with signs of life) with clinical viability thresholds used for treatment decisions, which typically begin around 22-24 weeks 1, 2
• Birth weight should not be adjusted for gestational age when determining legal viability 1
• The 350g weight criterion is specifically for cases where gestational age is unknown—it does not replace gestational age assessment when dating is available 1