What Is the Age of Fetal Viability?

If you’re faced with the possibility of giving birth very early, you’re likely filled with questions and concerns about fetal viability.

While it’s not possible to know all the answers about what will happen when your baby arrives, her gestational age and other key factors can help tell you some more about what the future might hold.

What is fetal viability?

In biological terms, viability is the ability to survive successfully. A fetus is considered viable if it has reached a stage of development where it is able to live outside of its mother’s womb.

Gestational age is a major determining factor in whether a baby will be viable, since the longer a fetus spends in the womb, the more fully developed it is when it enters the world. That said, there are other important considerations that can determine whether a baby born very early will ultimately survive. These include:

• Fetal weight. 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. 
• Fetal sex and plurality. Some research shows that girls are more likely to survive when born at earlier ages compared to boys, while preemie singletons often fare better than compared to early-born multiples. 
• The care a woman receives before birth. In some cases, treatments like corticosteroids, antibiotics or magnesium during pregnancy (often just before delivery) can help increase a baby’s chance for survival after birth. 
• The care a baby receives immediately after birth. Babies who are born in hospitals with an advanced neonatal intensive care unit (NICU) can more likely get the life-saving treatments they need right away. 

What is the point of fetal viability?

Fetal viability depends on many different factors, making it hard to pinpoint an age at which a baby born very, very early can definitely survive. 

Read This Next

What Type of Preemie Do You Have and When Can He Go Home From the Hospital?

The 20-Week Anatomy Scan

Stopping Birth Control

What Type of Preemie Do You Have and When Can He Go Home From the Hospital?

The 20-Week Anatomy Scan

Stopping Birth Control

Babies born before the third trimester (before 27 weeks of pregnancy) are considered periviable — or near the limit of viability. Because they’re still very underdeveloped, periviable babies require life-saving interventions immediately after delivery and receive advanced care in a high-level NICU setting in order to survive. Even with the best possible care, they may experience short- and long-term problems. 

While all births that occur before the third trimester pose extremely high risks, the odds for survival increase significantly at around 24 weeks. What’s more, medical advances mean that the survival rates for very premature babies — including those born before 24 weeks — are higher than ever. 

Here's what past research and the American College of Obstetricians and Gynecologists (ACOG) has found about viability based on gestational age:

• 26 weeks. As a fetus reaches its last week of the second trimester, the odds for viability are between 86 and 89 percent. 
• 25 weeks. Fetuses at 25 weeks have around a 67 to 76 percent chance of viability.
• 24 weeks. Doctors typically consider the 24-week mark to be the point of potential viability, though at that age, survival is still far from guaranteed. Fetal viability at 24 weeks ranges from 42 to 59 percent, according to ACOG. But some studies have found the chances for survival to run as high as 68 percent.  
• 23 weeks. Babies born at 23 weeks typically have a 23 to 27 percent chance for survival. 
• 22 weeks or earlier. The chances of viability before 23 weeks is low — about 5 to 6 percent.

How can I tell if my pregnancy is viable?

It’s not possible to know with total certainty how a fetus born very prematurely will fare. But your provider can estimate your baby’s chances for success based on things like her gestational age, her estimated weight, as well as other factors that can contribute to premature birth. 

They’ll also consider the level of care that you can receive throughout the remainder of your pregnancy and the care that your baby can receive after birth. 

Taking all of these variables into account, your provider can likely get a sense of the outlook. You can discuss those odds together and what care for your baby might entail after birth and use that information to make a decision about how best to move forward.  

Periviable birth vs premature birth

Periviable births are births that occur very, very prematurely — before the third trimester. A periviable fetus may have developed enough to survive beyond the womb, but not without advanced medical intervention and care. These types of births are very rare, occurring in just 0.5 percent of pregnancies.

Premature birth, on the other hand, is an umbrella term for any birth that occurs after 20 weeks and before 37 weeks of pregnancy. In 2019, 1 in 10 babies born in the U.S. were premature.

All premature babies are at higher risk for health and developmental problems and may require a stay in the NICU. However, babies born after 32 weeks are at significantly lower risk compared to those born sooner, according to the Centers for Disease Control and Prevention (CDC). 

Questions about fetal viability don’t always have clear answers. While older, more developed babies have a better chance at a more successful outcome, the success of periviable births also depend on the care that you and your baby receive before and after birth. And thanks to medical advances, the odds for even the teeniest preemies are getting better all the time.