Viability Week: When Can Your Baby Survive Outside the Womb?

Fetal viability is an anxiety-inducing but important milestone that can shape your decisions during your pregnancy.

Read on to learn what fetal viability actually means, which week your baby is likely to survive if she’s born early, and what implications this has for the both of you.

Usually, fetal viability means the point in your pregnancy when your baby has developed enough to survive outside your womb.

Somewhat confusingly, the American College of Obstetricians and Gynecologists (ACOG) notes that “viability” actually has two meanings. 1

• In early pregnancy, it refers to whether your pregnancy is expected to continue developing normally (if it’s expected to lead to a miscarriage, it isn’t viable).
• Later, it refers to whether your baby could survive outside of the womb if she were delivered prematurely.

Again, viability week relates to the second milestone: when preemies are likely to survive (with appropriate medical care).

While there isn’t a fixed point in your pregnancy where your baby’s chances of survival outside the womb increase, many experts in the US define viability week as week 24 of your pregnancy. 2 Some organizations place the threshold slightly later, but it’s always around then.

Babies are still considered “periviable” (borderline viable) at this point, and there’s no guarantee of survival.

Periviable vs. premature birth

If your baby is born before week 37 of your pregnancy, she’s considered premature. 3

A periviable birth, on the other hand, is a specific type of premature birth that happens between 20 weeks and 25 weeks of pregnancy.

Because earlier births result in more complications, periviable birth is riskier (as alluded to, the word “periviable” means “near viability,” i.e., on the very edge of viability).

If your baby is periviable, she may be able to survive, but (unfortunately) that’s far from guaranteed, and she will require a high level of intensive care. 4 5

Your baby’s viability outside the womb isn’t rigidly determined by her gestational age. It depends on several factors:

• Your baby’s health: Your baby’s weight has a big impact on her viability. Babies who weigh under 5.5 lb (2,500 g) are considered to have a low birth weight, which puts them at higher risk. Babies under 1.1 pounds (500 g) are in the highest risk category and are much less likely to survive. 6
• Your baby’s sex: There’s some research that suggests baby girls may have a slightly higher survival rate at earlier gestational ages than males. 7 8
• Your hospital’s capabilities: You’re likely to get better care if your hospital has access to a high-level neonatal intensive care unit (NICU) that provides the life-saving treatments that periviable and premature babies need. 1

What to know about carrying multiples

If you’re carrying multiples, that doesn’t directly affect how viable your babies are, but it does affect your odds of giving birth prematurely (when they’re less viable)

Broadly speaking, the more babies you carry, the more likely you are to deliver early. Twins have a risk of 60%, which climbs higher with triplets, quadruplets, etc. 9

Your baby’s gestational age is one of the primary metrics your doctor will use to gauge her development and health throughout your pregnancy.

If your doctor knows her gestational age, they can make an educated guess about when your baby’s organs will be fully developed or when she might be ready for birth. 10

Around 50% of babies born during this period may develop disabilities. (These can be serious, but aren’t always; they include mild ones like visual impairment, resulting in them needing glasses.) 11

When you’re 26 weeks pregnant, your baby’s chance of survival increases to 80%. Just about 10% of babies born at this stage still have disabilities, such as cerebral palsy and learning difficulties, along with hearing and visual impairments. 12

Generally, your baby’s chance of survival will improve the longer she spends in the womb, up until “term” (when you’re due to give birth if everything goes right).

Check out the table below to get an idea of how likely your baby is to survive if she’s born earlier: 1

If you’re facing the possibility of a preterm or periviable birth, try not to panic. Your doctor is there to help. They’ll assess your baby’s viability and provide you with the most accurate information possible about what to expect going forward.

Your doctor can explain all the potential risks and benefits of different interventions and help you make informed decisions about what to do.

How will your doctor track your baby’s viability?

In your early pregnancy, your doctor will assess your baby’s viability with a combination of:

• Ultrasound screenings
• Fetal heart rate monitoring

Medical interventions if your baby is at risk of premature birth

Doctors can provide a range of medical interventions to improve outcomes for both you and your baby if there are warning signs she might be born early: 13 14

• Tocolytic therapy: Your doctor may delay labor, which gives them time to administer antenatal steroids (to help your baby’s lungs develop) and magnesium sulfate (to protect her brain).
• Prophylactic or emergency cerclage: Your doctor may also perform a surgical procedure to stitch your cervix closed, which can help prevent premature birth. 15
• Antibiotics: These medications prevent infections, including group B strep, and delay premature rupture of membranes (PROM), where your water breaks too early, before you’re ready for labor.
• Cesarean delivery: Your doctor may perform a C-section if they’re concerned about your baby’s well-being or other complications.

What happens if you’re at risk of preterm labor?

If you’re at risk of preterm labor, try to find a hospital with a reputable NICU unit that can provide specialized, intensive care.

Your doctor will consider your baby’s chances of survival and her long-term health, which they’ll communicate to you, sometimes as part of family counseling.

If your baby’s health is poor, you may be given the option to pursue more intensive interventions, to forgo resuscitation, or to focus on palliative care that minimizes any suffering.

However, intensive care practices and technology, such as incubators and ventilators, can improve the chances of survival for premature babies. With careful monitoring and care, your doctor may be able to lower your baby’s risk of long-term issues, like brain damage or vision problems.

Taking care of your mental health if you have a low-viability pregnancy

Managing your mental health when faced with the possibility of a low-viability pregnancy can be challenging.

Fortunately, you don’t have to go it alone. Many hospitals offer counseling services specifically for expectant parents facing high-risk pregnancies. Ask your doctor to point you toward resources like this.

You can also look for support groups online if you don’t feel like you can handle another trip to the doctor.

Thankfully, advances in modern medicine have made it much easier for many babies born earlier than expected to continue to develop and thrive.

If you’re feeling anxious as you approach viability week, don’t be afraid to reach out for help. Your doctor is always there to offer you advice or even just a little reassurance.