Hailey Tran
Fetal viability refers to a baby's ability to survive outside the uterus without significant morbidity or disability. While gestational age is often used as a predictor of viability, it is not the only factor. Birth weight, fetal sex, plurality, maternal health, and access to advanced medical care also play a significant role in determining viability. Clinicians consider all these factors when assessing viability, particularly in the periviable period, to provide patients and their families with information to make shared decisions about their healthcare.
| Characteristics | Values |
|---|---|
| Fetal viability | The ability of a human fetus to survive outside the uterus |
| Determining viability | There is no definitive diagnosis of viability and no test that can determine whether a fetus could survive outside the uterus |
| Factors influencing viability | Birth weight, gestational age, availability of advanced medical care, sex, genetics, circumstances around delivery, availability of a neonatal intensivist healthcare professional, fetal organ maturity, environmental conditions, quality of the facility, mother's health |
| Periviable period | Clinicians consider several factors to determine a general percentage chance of survivability, which is an estimate created from data points reflecting a population average |
| Gestational age | Medical viability is generally considered to be between 23 and 24 weeks of gestational age. The odds for viability at 26 weeks are between 86% and 89%, at 25 weeks are between 67% and 76%, at 24 weeks are between 42% and 59% (or as high as 68% according to some studies), at 23 weeks are between 23% and 27%, and at 22 weeks or earlier are about 5% to 6% |
| Country-specific variations | The "grey zone" is considered to be 22 to 23 weeks in Sweden, 23 to 24 weeks in the UK, and 24 to 26 weeks in the Netherlands |
What You'll Learn
Birth weight
Historically, early efforts to define prematurity relied solely on birth weight. A birth weight of less than 2,300 or 2,500 grams was considered low birth weight (LBW). Today, birth weight is still a critical factor in determining viability, with weight and gestational age being inversely proportional—as gestational age increases, birth weight typically increases, improving the chances of viability.
In general, babies weighing at least 600 grams (about 1.3 pounds) at birth have a higher chance of viability compared to those who weigh less. At extremely low birth weights, such as 400 grams, survival is sporadic, and the lower limit of viability is typically defined as the gestational age or birth weight at which 50% of infants survive.
The relationship between birth weight and viability is further influenced by other factors, such as fetal sex, plurality, and the care received by the mother and infant. Research suggests that female infants may have a higher chance of survival at earlier gestational ages compared to male infants. Additionally, preemie singletons tend to fare better than early-born multiples.
The care provided to both the mother and the infant can also impact viability. Treatments like corticosteroids, antibiotics, or magnesium during pregnancy, especially before delivery, can enhance an infant's chances of survival. Moreover, infants born in hospitals with advanced neonatal intensive care units (NICUs) have improved access to life-saving treatments, further increasing their chances of viability.
While birth weight is a significant factor, it is important to recognize that viability is a complex determination that considers multiple variables. Gestational age, fetal organ maturity, environmental conditions, and the availability of advanced medical care all play a role in assessing viability. Therefore, healthcare professionals consider a comprehensive set of factors to estimate viability and make informed decisions about patient care.
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Gestational age
Fetal viability refers to a fetus's ability to survive outside the uterus, without significant morbidity or disability. This depends on many factors, including birth weight, sex, genetics, and the availability of advanced medical care. Gestational age is also a significant factor in determining fetal viability.
The odds of fetal viability at 26 weeks of gestation are between 86 and 89%. At 25 weeks, the chances of viability drop to 67-76%. Doctors typically consider the 24-week mark to be the point of potential viability, with a 42-59% chance of survival, although some studies have placed this figure at 68%. Babies born at 23 weeks have a 23-27% chance of survival, while those born before 23 weeks have a very low chance of survival (5-6%).
The definition of viability based on gestational age varies across countries. For instance, the grey zone is considered to be 22 to 23 weeks in Sweden, 23 to 24 weeks in the UK, and 24 to 26 weeks in the Netherlands.
While gestational age is a crucial factor in predicting fetal viability, it is not the sole determinant. The mother's health, such as uncontrolled diabetes or severe high blood pressure, can also impact the child's viability. Additionally, the quality of the medical facility, including the availability of neonatal intensive care units (NICU) and experienced healthcare professionals, plays a significant role in fetal viability.
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Mother's health
A mother's health is a significant factor in a child's viability. For example, uncontrolled diabetes in a mother can slow organ maturation, and infants of such mothers have a higher mortality rate. Severe high blood pressure before the eighth month of pregnancy can cause changes in the placenta, decreasing the delivery of nutrients and/or oxygen to the developing fetus and leading to problems before and after delivery. The rupture of fetal membranes before 24 weeks of gestation with amniotic fluid loss also markedly decreases the baby's chances of survival.
The quality of the medical facility is another factor that impacts fetal viability. This includes the availability of neonatal critical care services, neonatal intensive care units (NICU), Level I pediatric trauma care facilities, and medications such as corticosteroids. The experience and number of physicians and nurses in neonatology and obstetrics are also important considerations.
Additionally, the care a mother receives during pregnancy can increase the baby's chances of survival. Treatments such as corticosteroids, antibiotics, or magnesium, especially before delivery, can be beneficial.
While gestational age is a factor in predicting fetal viability, it is not the sole determinant. Sex, genetics, weight, circumstances around delivery, and access to medical care also play a role. Even with all these factors considered, it is challenging to predict survival accurately, and fetuses delivered during the periviable period may still experience significant morbidity and impairment.
In summary, a mother's health, the quality of medical care, and the treatments received during pregnancy all influence fetal viability. However, the complex interplay of various factors makes predicting survival a challenging task, and the decision-making process should involve both patients and healthcare professionals.
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Sex and plurality of the fetus
Fetal viability refers to a fetus's ability to survive outside the uterus. It depends on several factors, including birth weight, gestational age, and the availability of advanced medical care.
Gestational age is a major determining factor in fetal viability. The longer a fetus spends in the womb, the more developed it is when it is born. The American College of Obstetricians and Gynecologists (ACOG) has found the following viability rates based on gestational age:
- 26 weeks: 86-89% chance of viability
- 25 weeks: 67-76% chance of viability
- 24 weeks: 42-59% chance of viability, though some studies place this as high as 68%
- 23 weeks: 23-27% chance of viability
- 22 weeks or earlier: 5-6% chance of viability
However, there is no uniform gestational age that defines viability, and beliefs about it vary by country. For example, a 2018 study found that the "grey zone" for viability was considered to be 22 to 23 weeks in Sweden, 23 to 24 weeks in the UK, and 24 to 26 weeks in the Netherlands.
Other factors that influence viability include sex and plurality. Research shows that girls have a higher chance of survival when born prematurely compared to boys. Additionally, preemie singletons tend to fare better than early-born multiples.
The mother's health also plays a significant role in fetal viability. For example, uncontrolled diabetes in the mother can slow organ maturation, and severe high blood pressure before the eighth month of pregnancy can cause changes in the placenta, affecting the delivery of nutrients and oxygen to the fetus.
While these factors can help clinicians predict viability, there is no definitive test to determine whether a fetus can survive outside the uterus.
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Availability of advanced medical care
The availability of advanced medical care is a critical factor in determining fetal viability, which refers to a fetus's ability to survive outside the uterus. While gestational age and birth weight are often considered key indicators of viability, medical care plays a significant role in improving the chances of survival for premature infants.
The quality of medical care can vary between hospitals and countries, impacting fetal viability. Hospitals with advanced neonatal intensive care units (NICUs) can provide life-saving treatments immediately after birth, increasing the likelihood of survival for premature infants. The availability of specialized physicians and nurses in neonatology and obstetrics, as well as the presence of Level I pediatric trauma care facilities, can significantly influence an infant's chances of survival.
In high-income countries, the majority of extremely preterm newborns (less than 28 weeks gestational age) survive due to access to advanced medical care. On the other hand, in low-income countries, the lack of such medical resources results in a mortality rate of over 90% for these newborns. This disparity highlights the crucial role that advanced medical care plays in improving fetal viability.
The initiation of resuscitation and active treatment at very early gestational ages can vary between hospitals, leading to differences in survival rates. A study revealed that hospitals with access to advanced medical care, such as tertiary care institutions, tend to have more consistent practices and improved outcomes for infants born at 22, 23, 24, and 25 weeks.
Additionally, specific treatments and interventions during pregnancy can increase a baby's chances of survival. For example, the use of corticosteroids, antibiotics, or magnesium during pregnancy, especially before delivery, can positively impact fetal viability. These medical interventions demonstrate how the availability of advanced medical care extends beyond the newborn stage and can begin in utero to improve outcomes.
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Frequently asked questions
Fetal viability is the ability of a human fetus to survive outside the uterus.
Fetal viability depends on many factors, including birth weight, gestational age, the availability of advanced medical care, sex, genetics, and the mother's health.
Clinicians use ultrasound results, pregnancy hormone levels, and other clinical factors to assess fetal viability. However, there is no definitive test to determine whether a fetus is viable.
The age of viability varies and is generally considered to be between 23 and 26 weeks of gestation. However, this can differ due to various factors and may range from 22 to 26 weeks in different countries.
The outlook for preterm infants depends on their gestational age and other factors. Infants born before 23 weeks of gestation typically have a low chance of survival, while those born at 24 weeks have a higher chance of viability, although morbidity is still common.
