When Minutes Matter: Why Even a Single Early Steroid Shot Helps the Tiniest Babies

A large US study of 1,806 extremely premature babies shows that the hours between a mother's steroid injection and her baby's birth can improve the baby's chances

When a baby is about to be born far too early, doctors give the mother a steroid injection to help the baby's lungs and other organs get ready for life outside the womb. A large US study of 1,806 extremely premature babies found that even a single dose given just a few hours before birth was linked to better survival and less serious brain bleeding — and that every extra hour of exposure added a little more protection. The message for families and care teams is hopeful: even when there is very little time, that first injection appears to be worth giving.

Why this question matters

Babies born extremely early — here, between 22 and 27 weeks of pregnancy, when a full-term pregnancy is about 40 weeks — face some of the steepest odds in all of medicine. Their lungs, brains, intestines, and eyes are still unfinished. For more than fifty years, one of the most reliable tools doctors have had to improve their chances is a course of steroid injections given to the mother before birth. The idea traces back to a landmark 1972 trial by Liggins and Howie, who showed that giving mothers a steroid before a premature delivery reduced serious breathing problems and death in their babies [1]. Decades of later research confirmed and expanded that finding, showing that a complete course also lowers the risk of bleeding in the brain and a dangerous bowel condition called necrotising enterocolitis [2].

A "complete course" has a specific meaning: two injections of a steroid called betamethasone, given 24 hours apart [3]. That 24-hour gap is the heart of the problem this new study tackles. Premature labour is often fast and unpredictable, and sometimes a medical emergency for the mother or baby means the birth simply cannot wait. As a result, about one in four extremely premature babies is born after receiving only part of the course — often just a single dose, and sometimes only an hour or two before delivery [4]. Parents and doctors have long faced an anxious uncertainty in those moments: if there was only time for one shot, and the baby came soon after, did it do any good at all?

How the researchers looked for an answer

A team from the US National Institute of Child Health and Human Development's Neonatal Research Network — a group of leading academic hospitals that pool their data to study rare and difficult problems — set out to answer that question precisely [5]. They examined records from 15 hospitals for babies born between January 2016 and February 2021. To keep the comparison clean, they focused only on babies whose mothers had received a single dose of betamethasone within 24 hours of birth, and compared them with babies who had received no steroid at all. In total, 1,806 babies were included: 475 who received no steroid and 1,331 who received one dose.

The key measurement was simple: how many hours passed between the mother's injection and the baby's birth. Half of the single-dose babies were born within about four hours of the injection, and many within just an hour or two — so this was very much a study of short windows of time, measured in hours rather than days. The researchers then looked at whether more hours of exposure were linked to better outcomes, carefully accounting for other things that affect a premature baby's chances, such as how early the baby was born, the mother's health, and which hospital provided care. It is worth being clear about one point up front: this was an observational study, meaning the researchers watched what happened in real care rather than assigning treatments. That design can reveal strong patterns but cannot by itself prove that the timing alone caused the difference.

What they found

The pattern was consistent and encouraging. Overall survival to hospital discharge rose from about 65% among babies who received no steroid to about 74% among those who received a single dose [5]. More importantly, the benefit grew with time in a step-by-step way. Once more than about an hour and a half had passed between the injection and birth, survival was clearly better than with no steroid at all, and babies with the longest windows — more than about nine and a half hours — did best of all. Put another way, each additional hour of exposure was linked to roughly a 1% relative improvement in the chance of survival, which adds up meaningfully over several hours.

Some of the most striking results involved the brain. Serious bleeding in the brain — one of the most worrying complications for very premature babies — became substantially less common as the exposure window lengthened. Babies in the longest-exposure group had roughly a third lower risk of severe brain bleeding compared with babies who got no steroid. The combined risk of serious brain injury or death also fell steadily with each additional hour. For some other conditions, such as chronic lung disease and bowel injury on their own, the timing did not make a clear difference among babies who survived; the overall benefit was driven mainly by improved survival and by fewer of the most severe complications.

Why a single early dose can help so quickly

It may seem surprising that a single injection given only an hour or two before birth could matter. The biology helps explain it. Betamethasone passes quickly from the mother into the baby's bloodstream — it can be detected there within an hour — and it lingers, breaking down only slowly over roughly half a day [6]. So even one dose keeps working inside the baby across exactly the window this study examined. Experiments in animals have shown that the steroid begins to improve lung function within about 8 to 15 hours of exposure [7], and some of the steroid's effects on blood vessels may act even faster. In other words, the medicine does not need the full 24 hours to start doing good.

What this means for families and their babies

For parents facing the frightening possibility of a very early birth, the practical takeaway is reassuring: doctors should give that first steroid injection as soon as possible, and there is good reason to give it even when birth seems only hours away. This study turns a hopeful hunch into measured evidence and supports treating the first dose as an urgent, time-critical medicine. It fits with other research from the same network showing that steroid exposure improves survival even for the most premature babies, at 22 to 25 weeks [8], and with recent guidance supporting steroid use as early as 21 to 23 weeks in some pregnancies [9].

A few honest caveats matter. Because this was an observational study, part of the benefit of a longer window may reflect that those births were simply more controlled — there was time to move the mother to a specialised hospital, to prepare, and to deliver calmly — rather than the extra hours of medicine alone [10]. The researchers did their best to account for these factors, and the results held up, but no single study of this kind can be the final word. The babies were also cared for at large academic hospitals, where survival tends to be higher than average [11], so the exact numbers may differ elsewhere. And nothing in this research suggests delaying a birth that needs to happen; the lesson is to start the medicine sooner, not to wait longer.

What researchers are working on next

The clearest next step is making sure the first dose is given as fast as possible everywhere — building the steroid injection into emergency routines so no time is lost. Researchers also want to follow these children as they grow, to learn whether the early reduction in brain bleeding translates into better development in later childhood, and to study whether the two doses could safely be given closer together when time is short. For now, the finding offers families a genuinely encouraging piece of knowledge in a hard moment: when a baby is coming very early, even a single early steroid injection can help, and every hour counts [5].

References

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  2. Roberts D, Brown J, Medley N, Dalziel SR. Antenatal corticosteroids for accelerating fetal lung maturation for women at risk of preterm birth. Cochrane Database Syst Rev. 2017;3(3):CD004454. doi:10.1002/14651858.CD004454.pub3 ↩
  3. Committee on Obstetric Practice. ACOG committee opinion no. 475: antenatal corticosteroid therapy for fetal maturation. Obstet Gynecol. 2011;117(2 Pt 1):422-424. doi:10.1097/AOG.0b013e31820eee00 ↩
  4. Chawla S, Natarajan G, Shankaran S, et al. Association of neurodevelopmental outcomes and neonatal morbidities of extremely premature infants with differential exposure to antenatal steroids. JAMA Pediatr. 2016;170(12):1164-1172. doi:10.1001/jamapediatrics.2016.1936 ↩
  5. Chawla S, Wyckoff MH, Lakshminrusimha S, et al. Short Duration of Antenatal Corticosteroid Exposure and Outcomes in Extremely Preterm Infants. JAMA Netw Open. 2025;8(2):e2461312. doi:10.1001/jamanetworkopen.2024.61312 ↩
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  7. Ikegami M, Polk D, Jobe A. Minimum interval from fetal betamethasone treatment to postnatal lung responses in preterm lambs. Am J Obstet Gynecol. 1996;174(5):1408-1413. doi:10.1016/S0002-9378(96)70581-170581-1) ↩
  8. Carlo WA, McDonald SA, Fanaroff AA, et al. Association of antenatal corticosteroids with mortality and neurodevelopmental outcomes among infants born at 22 to 25 weeks' gestation. JAMA. 2011;306(21):2348-2358. doi:10.1001/jama.2011.1752 ↩
  9. Battarbee AN. Antenatal corticosteroids at 21-23 weeks of gestation. Obstet Gynecol. 2024;143(1):35-43. doi:10.1097/AOG.0000000000005352 ↩
  10. Melamed N, Shah J, Soraisham A, et al. Association between antenatal corticosteroid administration-to-birth interval and outcomes of preterm neonates. Obstet Gynecol. 2015;125(6):1377-1384. doi:10.1097/AOG.0000000000000840 ↩
  11. Rysavy MA, Li L, Bell EF, et al. Between-hospital variation in treatment and outcomes in extremely preterm infants. N Engl J Med. 2015;372(19):1801-1811. doi:10.1056/NEJMoa1410689 ↩