Most babies born at 37 weeks do well, but the delivery comes with measurably higher risks compared with waiting until 39 or 40 weeks. What was once lumped together as a single “term” window has been broken into finer categories precisely because research showed that outcomes at 37 weeks are not the same as outcomes at 39 weeks. The differences are real, and for some babies they matter a great deal, even though the vast majority go home healthy.
Why 37 Weeks Is No Longer Called “Full Term”
For decades, any delivery between 37 and 42 weeks was labeled “term,” and doctors tended to treat every week in that window as roughly equal. That changed in 2012 when a joint work group convened by leading obstetric organizations recommended splitting the window into four labels: early term (37 weeks through 38 weeks and 6 days), full term (39 weeks through 40 weeks and 6 days), late term (41 weeks through 41 weeks and 6 days), and post-term (42 weeks and beyond).1PubMed. Definition of term pregnancy The reclassification was driven by accumulating evidence that neonatal problems, particularly breathing difficulties, varied meaningfully across those weeks. A baby born at 37 weeks and 0 days is now considered early term, not full term.
Breathing Trouble Is the Main Short-Term Concern
The lungs are among the last organs to finish maturing. During the final weeks of pregnancy, the cells lining the air sacs ramp up their ability to absorb fluid through sodium channels, a process critical to the switch from living in liquid to breathing air.2PubMed. Physiology of fetal lung fluid clearance and the effect of labor When that process is incomplete, fluid lingers in the lungs and the newborn struggles to get enough oxygen. The clinical result can range from transient tachypnea, a mild and self-limiting fast-breathing episode, to full respiratory distress syndrome requiring supplemental oxygen or even ventilator support.
A study of more than 10,000 singleton newborns delivered at or after 37 weeks found that respiratory distress syndrome affected about 2.5% of early-term infants compared with about 1.5% of full-term infants.3PubMed Central. Risk factors for respiratory distress syndrome among high-risk early-term and full-term deliveries Those percentages sound small, and they are. But they mean the risk is roughly 60 to 70 percent higher in the early-term group, which adds up quickly across the millions of babies born every year. Labor itself plays a protective role: the hormonal cascade of natural labor helps trigger lung fluid clearance, so babies delivered by scheduled cesarean section before labor starts tend to have higher rates of breathing problems at any given gestational age.
Higher Chance of a NICU Stay
Breathing issues are one of the main reasons early-term babies end up in the neonatal intensive care unit. A large study comparing NICU admission rates by gestational week found a striking gap between 37 and 39 weeks. Among low-risk deliveries with no recorded complication, NICU admissions were about 7.2% at 37 weeks versus 3.3% at 39 weeks. The biggest absolute drop occurred between 37 and 38 weeks, and by 38 weeks the admission rate was no longer significantly different from 39 weeks for most categories of delivery.4PubMed Central. Neonatal Outcomes in Early Term Birth In other words, even a single extra week of gestation can make a noticeable difference in whether a newborn needs intensive care.
Hospitals that have introduced policies discouraging elective deliveries before 39 weeks have seen modest but real reductions in short NICU stays.5PubMed Central. NICU Admissions After a Policy to Eliminate Elective Early Term Deliveries Before 39 Weeks’ Gestation A NICU admission doesn’t just affect the baby. It separates parents from their newborn, disrupts early bonding and breastfeeding, and generates significant stress and cost. Many of these admissions are short, but they are often avoidable if delivery can safely wait.
Jaundice and Blood Sugar Dips
Beyond the lungs, a 37-week baby’s liver and metabolic systems are slightly less mature than those of a baby born two weeks later. The liver is responsible for processing bilirubin, the yellowish byproduct of red blood cell breakdown. When the liver can’t keep up, bilirubin accumulates and causes jaundice. Research has found that the incidence of hyperbilirubinemia is higher among babies born at 37 to 38 weeks compared with those born at 39 weeks.6JNKI (Jurnal Ners dan Kebidanan Indonesia) (Indonesian Journal of Nursing and Midwifery). A prospective observational study to evaluate the association of various maternal risk factors with increasing incidence of term neonatal jaundice Most neonatal jaundice is mild and resolves with phototherapy or simply with time, but severe untreated jaundice can cause lasting brain damage, so hospitals monitor bilirubin levels closely in early-term babies.
Low blood sugar in the hours after birth is another common concern. It is one of the most frequent conditions newborn care providers encounter, and while many cases are part of the normal transition to life outside the womb, some babies experience persistent or severe drops that require medical intervention.7PubMed Central. The screening and management of newborns at risk for low blood glucose Early-term infants are considered a higher-risk group for these episodes, which is one reason many hospitals have specific screening protocols for babies born before 39 weeks.
Effects on Brain Development and School Performance
The brain grows rapidly in the final weeks of pregnancy. Between 35 and 40 weeks, the fetal brain roughly doubles in volume, with critical white-matter connections forming and cortical folding accelerating. The observation that cesarean deliveries and early-term inductions have risen to account for a large fraction of all births has made this continued brain maturation an important medical and policy concern.8PubMed Central. Developmental scores at 1 year with increasing gestational age, 37-41 weeks
The effects show up years later, not just at birth. A well-known study of third-grade reading and math scores found that children born at 37 and 38 weeks scored significantly lower than those born at 39, 40, or 41 weeks, even after accounting for birth weight, socioeconomic status, and a range of other factors.9PubMed Central. Academic achievement varies with gestational age among children born at term A larger and more recent analysis put numbers on the gap: math scores for children born at 37 weeks were roughly 0.6 national percentile ranking points lower than for children born at 40 weeks, and 38-week births trailed by about 0.4 points. By contrast, scores at 39 weeks were virtually identical to those at 40 weeks.10JAMA Network Open. Association Between Gestational Age and Academic Achievement of Children Born at Term
These are small differences. Most parents would not notice them in everyday life, and no individual child’s school trajectory is determined by whether they were born at 37 weeks versus 40. But at a population level, when millions of early-term births accumulate year after year, even a fraction-of-a-percentile shift in average test scores has real educational implications. One study also found that induction of labor at 37 weeks was associated with modestly lower school performance scores at age 12 compared with pregnancies allowed to continue.11PubMed Central. Offspring school performance at age 12 after induction of labor vs non-intervention at term: A linked cohort study
A Small Increase in ADHD Risk
Beyond test scores, researchers have looked at whether early-term birth nudges the odds of neurodevelopmental conditions like ADHD. A national cohort study found that ADHD prevalence was about 5.2% among early-term children compared with 4.5% among those born full term. After adjusting for other factors, early-term birth was associated with about a 10 to 12 percent higher relative risk of an ADHD diagnosis, and the association held even after controlling for shared family factors using sibling comparisons.12PubMed Central. Preterm or Early Term Birth and Risk of Attention-Deficit/Hyperactivity Disorder: A National Cohort and Co-Sibling Study A separate pregnancy cohort study confirmed the pattern, finding that the risk for ADHD increased with lower gestational age regardless of birth weight.13PubMed. The Relationship Between Early Term Birth and the Risk of Later Childhood Mental Disorders Within a Pregnancy Cohort
A Finnish population-based study also found elevated risks for intellectual disability, autism spectrum disorder, and ADHD among early-term births, though the absolute increases were small.14PubMed Central. Neurodevelopmental risks of late-preterm and early-term births: a population-based study from Finland It is worth keeping perspective here. The overwhelming majority of early-term children never receive any of these diagnoses. The elevated risk is a statistical signal across hundreds of thousands of births, not a prediction for any individual baby. Still, for clinicians deciding whether to schedule an early delivery without a clear medical reason, these small cumulative risks tip the scale toward waiting.
When Delivering at 37 Weeks Is the Right Call
All of the above paints 37 weeks in a cautionary light, but that picture flips when there is a genuine medical reason not to wait. Preeclampsia, poorly controlled diabetes, placental problems, growth restriction, and certain infections can make the womb a riskier place than the outside world. In those situations, the slight immaturity of a 37-week baby is far outweighed by the danger of staying put.
A large Cochrane review pooling data from 31 trials of labor induction at or beyond 37 weeks found that, compared with continuing the pregnancy, induction was associated with substantially fewer perinatal deaths and fewer stillbirths, with no increase in cesarean delivery rates and no significant differences in breastfeeding success at discharge.15PubMed Central. Induction of labour at or beyond 37 weeks’ gestation These findings apply broadly, but the benefit is most dramatic when delivery is medically indicated rather than elective. A 16-year population-based study did find that induction in first-time mothers was associated with higher rates of instrumental delivery and cesarean section compared with spontaneous labor, along with higher rates of neonatal respiratory issues and even increased hospital admissions for infections in the years that followed.16PubMed Central. Intrapartum interventions and outcomes for women and children following induction of labour at term in uncomplicated pregnancies: a 16-year population-based linked data study The takeaway is not that induction is harmful, but that it should be driven by a real medical need rather than convenience or scheduling preference, especially before 39 weeks.
The Push Against Elective Early-Term Delivery
The American College of Obstetricians and Gynecologists has recommended for years that elective deliveries not be scheduled before 39 weeks.17PubMed. Decreasing elective deliveries before 39 weeks of gestation in an integrated health care system Despite this, elective early-term deliveries have remained common in the United States.18PubMed. Elective delivery before 39 weeks: the risk of infant admission to the neonatal intensive care unit Some hospitals have taken matters into their own hands by implementing “hard stop” policies that require a documented medical indication before an early delivery can proceed. One large academic center that introduced such a policy saw the proportion of deliveries before 39 weeks fall from about 33% to 26%.19PubMed. Neonatal outcomes after implementation of guidelines limiting elective delivery before 39 weeks of gestation
Why does the practice persist? Part of the answer is practical: scheduling a delivery is convenient for families and providers, and a 37-week baby often looks perfectly fine. The problems are statistical, not visible on the delivery table. You cannot tell which 37-week baby will end up in the NICU or which will struggle in school years later. The harms are subtle and probabilistic, which makes them easy to dismiss in individual cases even though they are clearly documented at the population level.
Whether Steroids Help at This Stage
For very premature babies, giving the mother corticosteroids before delivery is one of the most effective interventions in all of neonatal medicine, dramatically reducing lung disease and death. The question of whether the same strategy works for babies born at the late-preterm or early-term boundary is less clear. A review of the evidence concluded that while antenatal corticosteroids do reduce respiratory problems in this group, the benefit is small and confined mostly to transient tachypnea, the mildest form of breathing difficulty. Weighed against the possible harms of steroid exposure, the authors did not recommend routine corticosteroid use in the late-preterm and early-term period until further evidence emerges.20PubMed. The place of antenatal corticosteroids in late preterm and early term births This is an area where practice varies among hospitals, and you should ask your provider directly about their approach if a 37-week delivery is planned.
How Accurate Is Your Due Date, Anyway?
One complicating factor that rarely gets discussed is how precise the gestational age estimate actually is. The calendar date on your chart depends on either the date of your last menstrual period, an early ultrasound measurement, or some combination of the two. These methods don’t always agree. A study comparing the two dating methods found that early ultrasound reclassified a substantial number of births initially called 37 to 39 weeks (by menstrual dating) as preterm, and a smaller number of preterm births as term. The net effect was that ultrasound-based dating increased the preterm birth count significantly, mostly by reclassifying births that menstrual dates had placed just inside the term window.21PubMed. How does early ultrasound scan estimation of gestational age lead to higher rates of preterm birth?
This matters because a baby recorded as 37 weeks and 2 days might actually be 36 weeks and 4 days, or 38 weeks flat, depending on how the dates were calculated. A margin of error of even a few days can shift a baby from one risk category to another. If your provider is discussing an early delivery, it is worth asking how confident the dating is and whether the estimate is based on a first-trimester ultrasound, which tends to be the most accurate.
SIDS and Infant Mortality Beyond the Neonatal Period
The conversation about 37-week deliveries usually focuses on what happens in the first days or weeks of life, but some research has looked further out. A study of sudden infant death syndrome found that among babies delivered non-electively, the risk of SIDS declined with each additional week of gestation, with the odds dropping by about 22% per week even after adjusting for maternal and infant factors.22Pediatrics. Risk of Sudden Infant Death Syndrome and Week of Gestation of Term Birth Among elective deliveries, the trend was not significant. The authors speculated that the non-elective group included pregnancies with underlying complications that also contributed to SIDS risk, making it hard to separate the effect of gestational age itself from the conditions that led to early delivery.
A broader population study of low-risk women found that stillbirth and infant mortality rates were higher among births at 37 and 38 weeks compared with those born at later gestational ages. Births at 40 and 41 weeks had roughly 20 to 25 percent lower infant mortality compared with babies born after that point.23PubMed Central. Time of delivery among low-risk women at 37-42 weeks of gestation and risks of stillbirth and infant mortality, and long-term neurological morbidity The relationship between gestational age and survival is not a simple “longer is always better” curve, though. After 41 weeks, the risk of stillbirth begins to climb again, which is one reason post-term pregnancies are typically induced. The sweet spot, where both short-term and long-term outcomes look best, sits squarely at 39 to 40 weeks for uncomplicated pregnancies.
Gut Bacteria and Early Immune Development
An emerging area of research involves the infant gut microbiome, the community of bacteria that colonizes the intestines soon after birth and plays a key role in training the immune system. Disruptions to the microbiome’s early establishment, including preterm birth and cesarean delivery, have been associated with increased risk of long-term immune and metabolic problems.24PubMed Central. Nurturing the Early Life Gut Microbiome and Immune Maturation for Long Term Health Whether the two-week gap between 37 weeks and 39 weeks meaningfully alters the microbiome trajectory is not yet well established. Most of the microbiome research has compared very preterm babies with term babies, so the relevance to early-term birth specifically remains an open question. But it fits the broader pattern: the last weeks of pregnancy prime multiple systems, and cutting that period short, even slightly, may have downstream effects that science is still mapping.