A pregnancy at 37 weeks is not considered full term. It falls into the “early term” category, which covers 37 weeks 0 days through 38 weeks 6 days. Full term officially begins at 39 weeks 0 days and runs through 40 weeks 6 days. This distinction, established by the American College of Obstetricians and Gynecologists (ACOG), matters because those final two weeks of pregnancy make a measurable difference in a baby’s readiness for life outside the womb.
How Pregnancy Terms Are Classified
Before 2013, any birth between 37 and 42 weeks was lumped together as “term.” That changed when ACOG and other medical organizations recognized that outcomes vary significantly across those five weeks. The updated categories are:
- Early term: 37 weeks 0 days through 38 weeks 6 days
- Full term: 39 weeks 0 days through 40 weeks 6 days
- Late term: 41 weeks 0 days through 41 weeks 6 days
- Postterm: 42 weeks 0 days and beyond
Anything before 37 weeks is preterm. So while 37 weeks is no longer preterm, it sits at the very beginning of the early term window, not at the threshold of full term.
Why Those Last Two Weeks Matter
A baby at 37 weeks looks a lot like a baby at 39 weeks, but important development is still happening beneath the surface. The brain, lungs, and liver all undergo significant maturation in weeks 37 and 38. The brain, for instance, grows roughly a third of its weight during the final weeks of pregnancy. Lung cells are still ramping up production of surfactant, the substance that keeps air sacs from collapsing with each breath.
These differences show up clearly in birth weight. The median weight for a boy born at 37 weeks is about 3,080 grams (6 pounds 13 ounces), compared to 3,613 grams (7 pounds 15 ounces) at 40 weeks. For girls, the gap is similar: 2,968 grams at 37 weeks versus 3,470 grams at 40 weeks. That extra pound-plus reflects not just fat stores for temperature regulation but also organ growth that supports feeding, breathing, and blood sugar stability.
Breathing Risks at 37 Weeks
Respiratory problems are the most common complication for babies born in the early term window. At 37 weeks, the absolute risk of respiratory distress is around 4% for babies born after labor induction and as high as 12.4% for those delivered by planned cesarean section. These rates drop substantially by 39 weeks. The higher risk with cesarean delivery happens partly because the physical compression of labor helps squeeze fluid from the baby’s lungs, a step that gets skipped during a surgical birth.
Most breathing difficulties at 37 weeks are mild and temporary, often called transient tachypnea, where the baby breathes faster than normal for a day or two as fluid clears from the lungs. But some babies need supplemental oxygen or a stay in the NICU, which is why hospitals monitor early term newborns more closely in the first hours after birth.
Other Short-Term Risks
Beyond breathing, babies born at 37 weeks face higher rates of a few other complications compared to those born at 39 or 40 weeks. Jaundice is more common because the liver is slightly less mature and less efficient at processing bilirubin, the yellow pigment that builds up after birth. Early term babies are also more likely to have trouble maintaining their body temperature and blood sugar levels, and breastfeeding can take longer to establish because sucking reflexes are still developing.
These issues are generally manageable. Most 37-week babies do well with a bit of extra monitoring and support. But taken together, they explain why early term babies have higher rates of NICU admission than babies born even just two weeks later.
Long-Term Development Looks Reassuring
If your baby was born at 37 weeks (or you’re facing that possibility), the long-term picture is encouraging. A large sibling study published in The BMJ found that children born between 34 and 39 weeks showed no meaningful differences in cognitive ability by adolescence compared to those born at 40 weeks. Math scores, written language grades, and IQ were all statistically similar. Significant cognitive effects only appeared in children born before 34 weeks. For babies born at 37 or 38 weeks, IQ differences amounted to less than one point, which is well within the range of normal variation.
Why Doctors Wait Until 39 Weeks
Because of the short-term risks associated with early term birth, ACOG recommends against elective delivery before 39 weeks. This means that if your pregnancy is progressing normally, your provider will generally not schedule an induction or cesarean section before you reach 39 weeks 0 days. The reasoning is straightforward: when there is no medical reason to deliver early, those extra days in the womb reduce the chance of breathing problems, NICU stays, and feeding difficulties.
This guideline applies only to elective deliveries. If a medical condition like preeclampsia, gestational diabetes with complications, or problems with the placenta makes continuing the pregnancy riskier than delivering, your provider will recommend earlier delivery regardless of gestational age. In those cases, the timing balances the risks of an early term birth against the risks of staying pregnant longer. Lung maturity testing does not change the decision when there is a clear medical indication to deliver.
What 37 Weeks Means for You
If you’re at 37 weeks and everything is going smoothly, you’re in the home stretch but not quite at the finish line. Your baby is viable and would very likely do well if born today, but each additional day allows the lungs, brain, and liver to mature further. If your provider suggests waiting, those final weeks are the reason.
If you’ve already delivered at 37 weeks or are being told an early delivery is medically necessary, the odds are firmly in your favor. The vast majority of early term babies go home healthy, feed well within a few days, and show no lasting effects from arriving a couple of weeks ahead of schedule. The “early term” label reflects a small, real increase in short-term complications, not a prediction of problems.