What Is Fetal Viability?

A premature baby in an incubator

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Doctors often consider fetal viability the point at which a baby can be resuscitated at delivery and can survive without significant morbidity. Many times this age of viability is about 24 weeks gestation.

Many pregnant women, especially those who have previously experienced a pregnancy loss, anxiously await this milestone—and breathe a sigh of relief once they reach it. But pinpointing when fetal viability occurs is complicated, and many factors affect premature infant survival and outcomes.

Age of Viability

How far how along a pregnancy is plays a major role in determining viability. The exact age of viability continues to pose somewhat of an ethical dilemma, particularly about when and how much intervention should be done as the earlier a baby is born, the higher the risk of death and morbidity.

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.

24 Weeks

In many hospitals, 24 weeks is the point at which doctors will take steps in an attempt to save the life of a baby born prematurely. This generally means extreme medical intervention, potentially including mechanical ventilation and other invasive treatments followed by a lengthy stay in a neonatal intensive care unit (NICU). The baby may also require tubal assistance with eating and breathing.

Some hospitals may consider doing this when a baby born even earlier despite the greater potential for complications, disability, and death.

22 to 23 Weeks

In the hands of experienced specialists in state-of-the-art NICUs, babies born slightly earlier than 24 weeks may have a chance at survival. But unfortunately, that chance is slim, and outcomes for those who do survive are not optimal.

For babies born at 23 weeks or earlier who do survive, the odds of significant complications and/or lasting disabilities are much higher than for those that stay in the womb a few weeks longer.

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.

Also, 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.

Survival Statistics

The odds of survival increase as the pregnancy progresses, and even an extra 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.

For instance, one study found that the overall rates for survival and for survival without impairment ranged from 5.1% and 3.4% respectively among babies born at 22 weeks gestation. For 26 weeks of gestation, the percentages were significantly higher with a survival rate of 81.4% and survival without impairment rate of 75.6%.

It's also important to note that these rates are heavily dependent on a multitude of factors, including why the baby is born early and where the baby is cared for.

What Is Considered a Premature Birth?

According to the Centers for Disease Control and Prevention (CDC), the preterm birth rate is around 10%, with a higher incidence among younger (teen), Black (14.4% vs. 9.3% for white women and 10% for Hispanic women), and older (age 35 and above) mothers.

Very preterm births account for approximately 1.6% of all live births in the United States.

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

  • Extremely preterm: Gestational age at or below 28 weeks
  • Very preterm: Gestational age at or below 32 weeks
  • Moderately preterm: Gestational age between 32 weeks and 33 weeks and 6 days
  • Late preterm: Gestational age between 34 weeks and 36 weeks and 6 days

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

What Is a Perviable Birth?

A periviable birth is a birth that takes place near the limit of viability—usually defined as between 23 and 26 weeks gestation. Birth before 23 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:

  • 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 than multiples.
  • Oxygen deprivation: Birth complications that restrict fetal breathing, such as if the cord is wrapped around the neck, can affect survival rates.
  • Sex: On the whole, girls have higher survival rates than boys.
  • Steroid treatment prior to birth: Steroids taken by a mother 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

A baby’s brain undergoes much growth and development in the last weeks of pregnancy. As such, babies who are born very prematurely and survive face high odds of having some level of long-term effects.

The severity of these effects depends on many factors, including the need for and types of treatment received. Typically, the more intense the life-saving treatments, the greater the risk factors for these extremely small and fragile babies.

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:

  • 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 can vary greatly.
  • Mental health conditions: Preterm birth is linked to higher rates of social/emotional issues like anxiety, behavior problems, and depression.

Some facts to consider:

  • Between 20% and 50% of preterm infants born before 28 weeks will have lasting complications.
  • About 80% babies born at 26-weeks gestation will have long-term developmental or physical problems.

What to Ask Your Doctor

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 child at which gestational ages.

This is undoubtably a difficult situation to face. However, considering these issues before they are happening can give you a chance to ask all the pertinent questions and think through these tough decisions before they need to be made.

Among some questions parents who are facing a pre-term birth or who unexpectedly have one should ask:

  • What is the gestational age at which my baby was (or will be) born?
  • 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 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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