What Is Fetal Viability?

A premature baby in an incubator

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Many women, especially those who have experienced a past pregnancy loss, anxiously await fetal viability and breathe a sigh of relief after their pregnancy reaches the point at which the baby can survive if born early. However, pinpointing that date is complicated and many factors affect premature infant survival and the possibility of impairments or disabilities after birth.

According to the Centers for Disease Control and Prevention (CDC), in 2014, the preterm birth rate, around 10%, with a higher incidence among younger (teens) and older (35 and above) mothers. Very preterm births, which are defined as before 32 weeks, account for approximately 1.6% of all live births in the United States.

Age of Viability

How far how along a pregnancy is also plays a major role in determining viability. The exact age of viability continues to be somewhat of an ethical dilemma, particularly about when and how much intervention should be done as the earlier a baby is born the more likely they are to suffer major morbidity (complications or impairment). Viability is also a bit of a moving target that varies based on the quality of healthcare a baby has access to and in what part of the world they are born.

Doctors often define viability as a 50% chance of survival at birth.

24 Weeks

Most doctors define the age of viability as being about 24 weeks of gestation. In many hospitals, 24 weeks is the cutoff point for when doctors will use intensive medical intervention to attempt to save the life of a baby born prematurely. However, some hospitals may be able to try to save a baby born even earlier (see more on this below).

A baby born at 24 weeks would generally require extreme medical intervention, potentially including mechanical ventilation and other invasive treatments followed by a lengthy stay in a neonatal intensive care unit (NICU), possibly also requiring tubal assistance with eating and breathing. Additionally, the earlier a baby is born, the higher the risk of death and morbidity.

22 to 23 Weeks

In the hands of experienced specialists, babies born slightly earlier may have a chance at survival as well. Babies born at 23 weeks may survive in a state-of-the-art NICU, but the odds of survival, particularly without significant complications and/or lasting disabilities, are much lower. A 2015 study showed that babies born at 22 weeks may also have a small chance at survival, but death or serious health issues have an even higher probability of occurring.

Note that according to the American College of Obstetricians and Gynecologists, babies born before 23 weeks have a survival rate of just 5% to 6%. Of those that do survive, 98% to 100% have substantial complications and/or disability.

The odds of survival increase as the pregnancy progresses, and even an extra few days or week in the womb can make a big difference. In general, premature babies born closer to 37 weeks will be better off than those born before 28 weeks.

Survival Statistics

Based on information from the Quint Boenker Preemie Survival Foundation and the March of Dimes, below is the likelihood of survival for a baby born prematurely. It's important to note that these percentages are statistics and do not predict the survival of an individual baby.

Likelihood of Survival

  • 23 weeks: 17%
  • 24 weeks: 39%
  • 25 weeks: 50%
  • 26 weeks: 80%
  • 27 weeks: 90%
  • 28 to 31 weeks: 90 to 95%
  • 32 to 33 weeks: 95%
  • 34+ weeks: Almost as likely as a full-term baby

What is Considered a Premature Birth?

To provide a better idea of how early deliveries are categorized, doctors break down the gestational week ranges as follows:

  • Before 25 weeks: Extremely preterm
  • 26-32 weeks: Very preterm
  • 32-34 weeks: Moderately preterm
  • 34-36 weeks: Late preterm

Note that the vast majority of premature births take place during the late preterm period.

A periviable birth is a birth that takes place near the limit of viability—usually defined as between 22 and 26 weeks gestation. Before 22 weeks is usually considered previable, which means there is virtually no chance of survival.

Factors Affecting Fetal Viability

Multiple factors can play into whether or not a baby will survive a premature birth, including the following:

  • Birth weight: Larger babies have better survival rates. Low birth weight is independently linked to reduced odds of survival and a higher risk of disabilities and health problems.
  • Complications: If the early birth resulted from induction or c-section due to a medical condition, such as placental abruption or oxygen deprivation before the delivery, that condition can affect the baby's health and survival.
  • Number of babies: Singleton preterm births are more likely to be viable.
  • Oxygen deprivation: Birth complications that restrict fetal breathing can affect survival rates
  • Sex: Girls have higher survival rates than boys.
  • Steroid treatments prior to birth: Steroids prior to birth speed lung development, improving the odds of survival. Steroids can help the baby be able to breathe outside the womb.

Long-Term Effects

In addition to the risk of death, babies born very prematurely face high odds of having some level of long-term effects. In fact, 20% to 50% of preterm infants born before 28 weeks will have lasting complications. The severity of these effects depends on many factors, including the need for and types of treatment received in the immediate neonatal period.

Typically, the more intense the life-saving treatments, the greater the risk factors for these extremely small and fragile babies that are being kept alive. However, it is difficult to tell precisely which babies will have problems and how severe these problems will be later in life. Some common long-term effects of being born very prematurely include the following:

  • Cerebral palsy: This common neurological movement disorder is due to abnormal brain development (or injury).
  • Chronic health issues: These include the added risk of epilepsy, heart disease, feeding issues, infection, asthma, and sudden infant death syndrome (SIDS).
  • Cognitive impairment: Being born early may impact a child's intellectual development.
  • Developmental delays: Premature infants typically reach milestones later and have slower growth.
  • Hearing or vision problems: Vision and hearing deficits are common in preemies.
  • Learning disabilities: These children often have learning disabilities or other developmental impairments, but the severity of the disabilities or impairment vary heavily.
  • Mental health conditions: Preterm birth is linked to higher rates of socio-emotional issues like anxiety, behavior problems, and depression.

For every 26-week baby, about 20% of them will have no long-term problems. That leaves about 80% with some form of developmental or physical problem in their lives.

The baby’s brain undergoes much growth and development in the last weeks of pregnancy. According to the Quint Boenker Preemie Survival Foundation, 24% of babies born at the 26-week mark will have a moderate disability, such as visual/hearing impairment or cerebral palsy with the ability to walk, and 22% may have more severe disabilities like blindness, profound deafness, or cerebral palsy without the ability to walk.

Babies who are born early face the risk of learning disabilities and other problems, but the specific odds of these problems vary heavily depending on factors such as birth weight and whether or not there was oxygen deprivation before birth.

If you expect to deliver an extremely premature baby, start a conversation with the doctors who will be caring for your baby about what type of resuscitation you would want for your baby at which gestational ages.

What to Ask Your Doctor

There is a wide range of possibilities that are very specific to the situation at hand. Questions to consider asking include:

  • Was the baby oxygen-deprived prior to birth? What are the expected consequences of that? What tests were run to check the severity? 
  • What problems should I watch for after discharge? In the first year? When my child starts school?
  • What is the gestational age at which my baby was (or will be) born?
  • What type of follow-up will my baby need? Is there an early intervention program?
  • What types of interventions have been used or will be used in my baby’s care? What are the risks and benefits of each of these treatments? What are the alternatives?

A Word From Verywell

There are so many variables to consider when delivering a preterm baby for both parents and medical professionals. It is not merely a discussion of whether the baby survives the birth, but what the long-term outcomes for your baby are.

If your baby was born prematurely or you expect your baby to be born prematurely, talk at length with your baby's doctor so you can be as prepared as possible and get the support you may need. Parental support groups are invaluable to both yourself and others.

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Article Sources
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