Premature Birth and Survival Statistics

Birth weight and steroids affect a preemie's odds of survival

Photodisc/Photodisc/Getty Images

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.

At what point, though, is that really true? The answer is somewhat complicated, although it's good to know that survival rates have risen greatly since the 1980s.

    Age of Viability

    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 six 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 better off than those born before 28 weeks.

    Factors Affecting Survival

    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 into whether or not a baby will survive premature birth, including 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 is whether the doctors had time before the birth to treat the baby with steroids to speed up lung development. The 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 unexpectedly premature because the steroids can make a difference in whether or not the baby is able to breathe outside the womb.

    It's also worthy to note that girls are more likely to survive very early premature birth, as are babies born in singleton vs. multiple pregnancies.

    Survival Statistics

    Based on information from the Quint Boenker Preemie Survival Foundation and the March of Dimes, here is the likelihood of a 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. 

    Length of PregnancyLikelihood of Survival
    23 weeks17 percent
    24 weeks39 percent
    25 weeks50 percent
    26 weeks80 percent
    27 weeks90 percent
    28-31 weeks90 to 95 percent
    32-33 weeks95 percent
    34+ weeksAlmost as likely as a full-term baby
    Sources: March of Dimes, Quint Boenker Preemie Survival Foundation

    Risk of Disabilities

    In addition to the risk of death, babies born very prematurely can face high odds of having some level of learning disabilities or other developmental impairment, but the severity of the disabilities or impairment can vary heavily. This can depend on many factors, including the need for and types of treatment received in the immediate neonatal period. The more intense treatment, sometimes the more intense the risk factors for these extremely small and fragile babies.

    In essence, the very procedures that are life-saving also have the ability to limit their babies' abilities as they grow up.

    The problem is, it is nearly impossible to tell which babies will have problems and how severe these problems will be later in life.

    For every 26-week baby, about 20 percent of them will have no long-term problems. That leaves about 80 percent with some form of developmental or physical problem in their lives. Though it is important to note again that these can vary in severity.

    About 34 percent of babies born at the 26-week mark will have a mild disability. A mild disability is defined as something like near-sightedness or minor cognitive impairment. So even within this category, you can see that there is still a wide range of potential problems.

    Twenty-four percent of babies born at the 26-week mark will have a moderate disability. A moderate disability includes problems such as visual/hearing impairment or cerebral palsy with the ability to walk. Cerebral palsy in and of itself can drastically vary from person to person. Early intervention can also help with preventing or lessening some of the symptoms.

    The remaining 22 percent will have severe disabilities. This can include blindness or profound deafness. It can also include cerebral palsy with no ability to walk. This is typically what people think of when they consider developmental disabilities following a preterm birth.

    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.

    This is true, even for babies who you would not necessarily categorize as preterm, including those born in the early-term. The baby’s brain undergoes much growth and development in the last weeks of pregnancy.

    If you expect to deliver an extremely premature baby, talk early 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.

    A Word From Verywell

    As you can see, there is much more to discuss when it comes to preterm birth. It is not merely a discussion of whether the baby survives the birth, but what the long-term outcomes for this baby are.

    If your baby was born prematurely or you expect your baby to be born prematurely, be sure to talk at length with your baby's doctor so are prepared as possible.

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

    • What is the gestational age at which my baby was (or will be) born?
    • Was the baby's oxygen deprivation prior to birth? What are the expected consequences of that? What tests were run to check the severity? 
    • 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?
    • 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?

    Sources:

    March of Dimes. (October 2013). "Fact Sheet: Preterm Birth."

    Tyson JE et al. Intensive Care for Extreme Prematurity – Moving Beyond Gestational Age. N Engl J Med. 2008 Apr 17;358(16):1672-81.

    Quint Boenker Preemie Survival Foundation. (n.d.). "Premature Birth Statistics." 

    Zisk JL, Genen LH, Kirkby S, Webb D, Greenspan J, Dysart K. Do Premature Female Infants Really Do Better Than Their Male Counterparts? Am J Perinatol. 2011 Mar;28(3):241-6.

    Continue Reading