From the Guidelines
A viable pregnancy is generally considered to have reached a gestational age of 24 weeks, as indicated by the most recent and highest quality study 1. At this point, the fetus has approximately a 50% chance of survival outside the womb with intensive medical intervention. Viability continues to improve with each additional week of gestation, with survival rates increasing significantly by 28 weeks and even more by 32 weeks. The concept of viability is important for medical decision-making but has evolved over time with advances in neonatal care. Babies born before 24 weeks may occasionally survive but often face significant health challenges and complications. After 24 weeks, healthcare providers typically shift their approach to include more aggressive interventions to save the baby if complications arise. This threshold is based on lung development and other organ maturity that allows for potential survival outside the uterus. However, it's essential to understand that viability exists on a spectrum rather than being a fixed point, and outcomes depend on many factors including birth weight, sex, presence of congenital anomalies, and access to advanced neonatal intensive care, as noted in the study 1. Some key factors that affect viability, in addition to gestational age, include estimated fetal weight, multiple gestations, fetal genetic diseases, and fetal anomalies, as discussed in the study 1. The periviable period, defined as 20 0/7 to 25 6/7 weeks of gestation, is a critical time when the fetus may survive outside the uterus with life-sustaining interventions but still with a high risk of death or severe morbidities, as described in the study 2. Rates of neonatal survival to discharge in this period range from 23% to 27% for births at 23 weeks of gestation, 42% to 59% for births at 24 weeks of gestation, and 67% to 76% for births at 25 weeks of gestation, as reported in the study 1. Deliveries before 23 weeks of gestation have a 5% to 6% neonatal survival rate, and the rate of serious morbidity is 98% to 100% among the survivors, highlighting the importance of considering the individual circumstances and parental preferences when making decisions about resuscitation and support, as emphasized in the study 3. In formulating a plan of care for periviable neonates, clinicians should discuss with parents whether their goal is optimizing survival or minimizing suffering, and the approach to antenatal and postdelivery care may differ dramatically depending on parental preferences regarding resuscitation, as noted in the study 3. A decision to proceed with resuscitation always should be informed by individual circumstances, including specific clinical issues, family values and wishes, and ongoing evaluation of fetal or neonatal condition, as discussed in the study 3. Ultimately, the determination of viability and the decision to provide life-sustaining interventions should be made on a case-by-case basis, taking into account the unique circumstances of each pregnancy and the preferences of the parents, as emphasized in the study 1.
From the Research
Definition of Viable Pregnancy
- A viable pregnancy is defined as a fetus that has reached a stage of development where it can survive outside the uterus with the help of medical technology 4.
- The gestational age at which a fetus is considered viable varies depending on the availability of medical technology and resources.
Gestational Age of Viability
- In the United States, viability is estimated to occur at approximately 24 weeks of gestational age 4.
- A study found that at 25 weeks of gestation, mortality was 44.4%, and at 26 weeks, it was 24.4% 4.
- Another study reported that the majority of obstetrician-gynecologists consider 24 weeks to be the earliest age a fetus is potentially viable 5.
Factors Affecting Viability
- The availability of medical technology and resources plays a significant role in determining viability 4.
- Physician characteristics, such as experience and specialty, can also influence judgments of viability and decisions regarding medical intervention 5.
- The use of tocolytics, such as nifedipine and indomethacin, can help postpone preterm birth and improve neonatal outcomes 6, 7.