Can Twins Survive at 24 Weeks? Viability and Outlook

Twins born at 24 weeks of gestation can survive, and many do, but their odds are meaningfully worse than those of a singleton born at the same age. A large European population-based study found that between 24 and 27 weeks, twins had roughly 50 percent higher adjusted odds of dying compared to singletons born at the same gestational age. Whether a given pair of 24-week twins pulls through depends on a tangle of factors that singleton pregnancies rarely face: how the babies share their placenta, whether one twin is much smaller than the other, and complications unique to multiples like twin-to-twin transfusion syndrome.

How Survival Compares to Singletons at the Same Gestational Age

At most gestational ages, twins and singletons born very preterm actually have similar mortality rates. The gap opens up specifically at the extreme edge of viability. A UK population-based study covering births under 30 weeks found that twins had about twice the infant mortality of singletons between 23 and 25 weeks (an odds ratio of roughly 2.0), but the two groups converged at later gestational ages.¹ A European cohort (the MOSAIC study) found the same pattern, with twins at 24–27 weeks carrying 50 percent higher adjusted odds of death, and that excess risk concentrating in same-sex pairs where the babies’ birthweights were far apart.²

Not every study agrees on the size of the gap. A regional perinatal cohort found that death or severe disability at two years was about 30 percent in twins versus 23 percent in singletons born at 30 weeks or earlier, but this difference was not statistically significant.³ The honest read of the evidence is that 24-week twins face a real but modest survival disadvantage compared to 24-week singletons, and much of that disadvantage traces to specific complications rather than twinning itself.

Why Placenta Type Changes the Equation

The single most important biological distinction among twins, from a survival standpoint, is chorionicity: whether the babies share a placenta or each have their own. Fraternal (dizygotic) twins nearly always have separate placentas (dichorionic). Identical twins can be dichorionic, share a placenta with separate sacs (monochorionic-diamniotic, or MCDA), or share both a placenta and a sac (monochorionic-monoamniotic, or MCMA). Each arrangement carries different risks.

A large study tracking twin pregnancies from the first trimester found that among twins alive at 24 weeks, those with separate placentas had a perinatal death rate of about 1 percent after that point. For MCDA twins the rate jumped to 2.5 percent, and for MCMA twins it reached roughly 9 percent.⁴ Most of the additional risk in monochorionic twins comes from complications that arise before 24 weeks: shared blood vessels in the placenta can cause unequal blood flow, and the overall mortality difference between monochorionic and dichorionic twins largely accumulates in earlier pregnancy rather than after 24 weeks.⁵ If monochorionic twins make it to 24 weeks alive, they still face elevated risk, but the steepest drop-off is already behind them.

Twin-to-Twin Transfusion Syndrome

The most feared complication unique to monochorionic twins is twin-to-twin transfusion syndrome, or TTTS, where abnormal blood vessel connections in the shared placenta allow blood to flow unevenly from one baby (the “donor”) to the other (the “recipient”). In advanced stages presenting before 26 weeks, the natural perinatal loss rate without treatment is grim, reported at 70 to 100 percent. Laser treatment of the connecting vessels improves things considerably, but even after treatment the perinatal mortality rate remains in the range of 30 to 50 percent, with a 5 to 20 percent chance of long-term neurological problems in survivors.⁶

For families facing TTTS at or near 24 weeks, the picture is especially fraught because the babies are right at the border of viability. If laser treatment stabilizes the pregnancy and buys even a few more weeks of gestation, outcomes improve dramatically. But if delivery becomes necessary immediately after the procedure, the babies face all the usual hazards of extreme prematurity on top of any damage from the transfusion imbalance itself.

When One Twin Is Much Smaller Than the Other

Growth discordance, where one twin is substantially smaller than its sibling, is another risk factor that looms large at 24 weeks. In monochorionic twins with selective fetal growth restriction diagnosed early (at 16 or 20 weeks), the survival rate was about 85 percent, compared with 98 percent when growth restriction was first identified later, at 30 weeks.⁷ Early-onset growth restriction is more dangerous because it often signals a fundamentally uneven placental share, and these pregnancies tend to require earlier delivery.

Growth discordance also affects specific complications after birth. The smaller twin in a discordant pair is more likely to develop necrotizing enterocolitis (NEC), a dangerous bowel inflammation. A study of identical twins confirmed that within discordant pairs, the lower-birthweight twin developed NEC more often, independent of genetics and shared maternal factors.⁸ Growth restriction also independently predicts a patent ductus arteriosus that needs treatment, adding yet another cardiovascular hurdle for the smaller baby.⁹

What Antenatal Steroids Do for Twins

When preterm delivery looks imminent, the most important medical intervention before birth is a course of corticosteroids given to the mother. These accelerate lung maturation and reduce the risk of respiratory distress, brain bleeds, and death in the first weeks of life.¹⁰ There has been some debate about whether steroids work as well in twins as in singletons, since most of the original clinical trials were done in singleton pregnancies and the pharmacokinetics could differ when two fetuses share the maternal blood supply.

The evidence so far is reassuring. A Korean national cohort study found that antenatal steroids significantly reduced mortality in babies born between 23 and 28 weeks, with the benefit holding in twins. The steroid-treated group had roughly 25 percent lower mortality and meaningfully reduced rates of severe brain bleeds.¹¹ Timing matters: the French EPIPAGE-2 cohort found that a single course given within seven days of delivery cut in-hospital mortality by about 70 percent and dramatically reduced severe brain injury. But when more than seven days elapsed between the steroid course and delivery, the mortality benefit faded.¹² This underscores the clinical challenge: predicting exactly when twins at 24 weeks will actually deliver is notoriously difficult.

Life in the NICU at 24 Weeks

Babies born at 24 weeks, whether twins or singletons, face a gauntlet of organ-system challenges in the neonatal intensive care unit. For twins, some of these hazards are amplified.

Lungs are the most immediate concern. At 24 weeks, the lungs are profoundly immature, and nearly all babies at this age require breathing support and surfactant, a substance that keeps the air sacs from collapsing. An interesting wrinkle for twins is that the smaller baby in a growth-discordant pair sometimes does slightly better with respiratory distress than the larger one. A study of identical twins found that the larger twin was about twice as likely to develop respiratory distress syndrome and needed surfactant more often.¹³ The explanation likely involves fetal stress responses that accelerate lung maturation in the growth-restricted baby, a small silver lining in an otherwise concerning situation.

The heart presents its own challenge. A blood vessel called the ductus arteriosus, which normally closes shortly after birth, often stays open in extremely premature babies and can disrupt blood flow to the lungs and other organs. About 70 percent of babies born at 23–24 weeks develop a hemodynamically significant patent ductus arteriosus, compared with roughly 59 percent of those born at 25–28 weeks.¹⁴ For twins, monochorionic placentation makes drug treatment for this condition less likely to succeed, meaning more of these babies end up needing surgical closure.⁹

The brain is vulnerable to bleeding because the blood vessels in the developing brain at 24 weeks are extremely fragile. One study found that severe intracranial bleeding (grades III and IV) occurred nearly four times more often in preterm twins than in singletons.¹⁵ White-matter injury occurred about twice as often. Other researchers have found less dramatic differences, with one study reporting no significant excess of brain bleeds in preterm twins.¹⁶ The discrepancy probably reflects differences in the mix of chorionicity and growth discordance in each study’s population.

Eyes are another area of concern. Retinopathy of prematurity (ROP), where abnormal blood vessels grow in the retina, is extremely common at 24 weeks. In very low birthweight twins, the odds of developing any ROP at 24 weeks were about 58 times higher than at 29 weeks.¹⁷ Modern screening and treatment, including laser therapy and injections, can prevent the worst outcomes, but the sheer frequency of ROP at this gestational age means nearly every 24-week twin will be monitored closely.

Does Birth Order Make a Difference?

Parents of twins often wonder whether the first or second baby to be delivered fares better. At very preterm gestational ages, the answer is mostly reassuring. A large retrospective study of very low birthweight twin pairs found that the second twin had a slightly higher rate of respiratory distress syndrome and surfactant use, but no significant difference in overall survival or survival without major complications.¹⁸ The exception was second twins delivered by cesarean section after the first twin was born vaginally, a scenario associated with worse survival.

At later gestational ages, birth order matters more. A large cohort study found that among twins born at or after 36 weeks by non-planned cesarean delivery, nine second twins died compared with zero first twins. But among preterm twins, the number of delivery-related deaths was identical for first and second babies.¹⁹ At 24 weeks, the risks from prematurity itself so thoroughly dominate that the second twin’s brief additional time in the birth canal does not meaningfully add to the hazard.

Vaginal Versus Cesarean Delivery at Extreme Prematurity

The ideal mode of delivery for extremely preterm twins is contested. For very low birthweight twins overall, one study found no significant difference in neonatal mortality between vaginal and cesarean delivery, though the vaginal group had a higher rate of brain bleeds.²⁰ Interestingly, respiratory distress was actually less common after vaginal birth, likely because the physical compression of labor helps squeeze fluid out of the lungs. For the second twin presenting in a non-head-first position, vaginal delivery at very early gestational ages appeared no riskier than cesarean, at least by five-minute Apgar scores.²¹

In practice, many obstetricians lean toward cesarean delivery at 24 weeks, especially for monochorionic twins or when the presenting twin is not head-first. The evidence does not overwhelmingly favor one approach, and individual circumstances such as fetal positioning, cervical dilation, and the presence of complications like TTTS or cord entanglement often dictate the decision more than any general guideline can.

Long-Term Developmental Outlook

Parents understandably want to know not just whether their 24-week twins will survive, but how they will develop over the years. The reassuring headline is that being a twin, by itself, does not appear to impose a major long-term neurodevelopmental penalty beyond what extreme prematurity alone causes. A cohort study comparing very preterm twins and singletons found no significant differences in general developmental scores at age two or age five.²² The one caveat: monochorionic twins showed lower scores in language and performance domains at five years after statistical adjustments, hinting that the complications of a shared placenta leave subtle marks even in children who escape major disability.

Gestational age at birth remains the strongest predictor of long-term outcomes. A study stratifying twins by delivery timing found that neonatal death was 14 percent in the most premature group and dropped to zero in twins born closer to term. Minor adverse outcomes like needing speech or occupational therapy affected the vast majority of the earliest-born twins, at 83 percent, compared to 38 percent of those born later.²³ For 24-week twins, this means that many survivors will need developmental support services through childhood, even if they avoid catastrophic complications.

The Financial Weight of a 24-Week NICU Stay

Extreme prematurity is extraordinarily expensive, and having two babies in the NICU simultaneously roughly doubles the financial burden. A Canadian study found that for infants who survived past the first three days, the median NICU cost at 24 weeks was about $155,000 per baby.²⁴ American data puts the figure even higher: a commercially insured population showed average healthcare expenditures of roughly $604,000 per 24-week infant in the first year.²⁵ For twins at 24 weeks, you can roughly double those numbers, though some shared family costs (parental leave, transportation) do not scale linearly. Notably, when researchers have compared twin and singleton NICU costs at the same gestational age, the per-baby costs are similar; twins are not individually more expensive, there are simply two of them.²⁶

Emotional Toll on Parents

The psychological burden on parents of 24-week twins is intense and underappreciated. Having two babies in critical condition simultaneously creates a relentless cycle of worry, decision-making, and time spent at the bedside. One study found that about a quarter of mothers of extremely low birthweight infants showed signs of post-traumatic stress disorder following the birth.²⁷ For twin parents, the stress may be compounded by discordant outcomes: one twin doing well while the other deteriorates, or the agonizing possibility that the babies will follow entirely different trajectories.

Social workers and psychologists embedded in NICUs increasingly recognize that parental mental health is not a secondary concern. Parental stress and depression affect bonding, breast milk production, and the ability to participate in developmental care like skin-to-skin contact, all of which feed back into the babies’ outcomes.

Ethical Decisions at the Threshold

Twenty-four weeks sits squarely in what neonatologists call the “gray zone” of viability, typically defined as roughly 22 to 25 weeks. In this window, hospitals and parents must decide whether to attempt full resuscitation. For singletons, outcome prediction tools can weigh factors like estimated weight, sex, and whether steroids were given. For twins, these decisions become tangled because the two babies may have different estimated weights, different presentations, and different levels of compromise. An ethical analysis noted that outcome prediction tools can generate meaningfully different survival estimates for each twin in a pair, raising the uncomfortable question of whether parents should be offered the option of resuscitating one baby but not the other.²⁸

In practice, selective resuscitation of twins is rare. Most neonatal teams and families opt to resuscitate both or neither, but the conversation itself illustrates how the existence of a co-twin transforms every decision at the edge of viability. A family deciding about comfort care for a singleton faces a devastating choice; a family with twins faces that choice potentially doubled, and complicated by the knowledge that one baby’s outcome may be very different from the other’s. Hospitals with more experience managing extreme prematurity tend to have more structured protocols for these conversations, and parents are often guided through the decision over hours or days rather than in a single meeting.

Necrotizing Enterocolitis at the Threshold

One complication that deserves special mention for 24-week twins is necrotizing enterocolitis. NEC is an inflammatory bowel disease of premature infants that can rapidly become life-threatening. Among babies born at the threshold of viability, more than half were treated for NEC in one case-control study, and about 30 percent needed surgery.²⁹ Surgical NEC in twin pregnancies has been reported in roughly 20 percent of affected babies.³⁰

What makes NEC particularly relevant for twins is the role of birthweight discordance. In identical twins, researchers have been able to isolate the effect of birthweight from genetics and maternal factors. The lighter twin within a discordant pair consistently develops NEC more often, and pairs where both babies had lower birthweights and earlier delivery had higher overall NEC rates.⁸ Breast milk feeding, which lowers NEC risk, can be logistically harder for parents of twins to sustain, adding a practical dimension to an already dangerous medical problem.