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Premature Birth and Viability

At What Point in Pregnancy Can a Baby Survive Premature Birth?

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Updated July 14, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Many women, especially those who are anxious after a past pregnancy loss, breathe a sigh of relief after the pregnancy reaches the point at which the baby would be able to survive if born early. What point, though, is that really? The answer is somewhat complicated.

Premature Birth Survival

Strictly speaking, 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. A baby born at 24 weeks would generally require a lot of intervention, potentially including mechanical ventilation and other invasive treatments followed by a lengthy stay in a neonatal intensive care unit (NICU).

In the hands of experienced specialists, though, babies born slightly earlier may have a chance at survival. Babies born at 23 weeks may survive with these specialists in a state-of-the-art NICU, but the odds of survival are much lower. The earliest baby to have ever survived premature birth was born at 21 weeks and 6 days, and this was reported in the news as having been a "miracle."

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

Factors that Affect Premature Babies' Survival

But the matter is not always as simple as being past a particular point in the pregnancy at the time of the birth. Multiple factors can play in to whether or not a baby will survive premature birth, for example, the baby's birth weight. Low birth weight is independently linked to reduced odds of survival and a higher risk of disabilities and health problems.

In addition, if the early birth resulted from induction or C-section due to a medical condition, such as placental abruption, the effects of that condition can affect the baby's health and survival also — such as if there was oxygen deprivation before the delivery.

Another factor can be if doctors had time before the birth to treat the baby with steroids to speed up lung development. The patient/mother gets the steroids, which then pass through the placenta to the fetus. A very premature baby treated with steroids before birth is more likely to survive than a baby born premature unexpectedly, because the steroids can make a difference in whether or not the baby is able to breathe outside the womb.

Girls may also be more likely to survive very early premature birth, as are babies born in singleton vs. multiple pregnancies.

Odds of a Premature Baby's Survival by Length of Pregnancy

Length of Pregnancy Likelihood of Survival
23 weeks 17%
24 weeks 39%
25 weeks 50%
26 weeks 80%
27 weeks 90%
28-31 weeks 90-95%
32-33 weeks 95%
34+ weeks Almost as likely as a full-term baby
Sources: March of Dimes, Quint Boenker Preemie Survival Foundation
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