Late preterm refers to babies born between 34 weeks 0 days and 36 weeks 6 days of gestation. These infants arrive three to six weeks before their due date, and while they often look similar to full-term newborns, they face a distinct set of health challenges because of the development they missed in the final stretch of pregnancy. The American College of Obstetricians and Gynecologists previously called these births “near term,” but the name was changed to “late preterm” to better reflect the medical risks involved.
Late preterm births are not rare. Provisional CDC data for 2024 puts the U.S. late preterm birth rate at 7.69%, meaning roughly 1 in 13 babies arrives in this window. That makes late preterm the largest category of preterm birth by a wide margin.
How Late Preterm Fits Into Preterm Categories
Any birth before 37 weeks 0 days of gestation counts as preterm. Within that umbrella, the standard breakdown is:
- Very preterm: before 32 weeks 0 days
- Moderately preterm: 32 weeks 0 days through 33 weeks 6 days
- Late preterm: 34 weeks 0 days through 36 weeks 6 days
A baby born at 37 weeks 0 days is considered “early term,” not preterm. The distinction matters because each additional week in the womb significantly reduces the likelihood of complications. A baby born at 36 weeks and 5 days may seem nearly full term, but their lungs, brain, and liver are still meaningfully less mature than those of a baby born even two weeks later.
Why the Last Few Weeks Matter So Much
The final six weeks of pregnancy are a period of rapid organ maturation. Fetal brain volume increases by roughly 2.3 milliliters per day during the third trimester, which means a baby born at 34 weeks misses out on weeks of critical brain growth. The lungs are still producing surfactant, the substance that keeps air sacs from collapsing. The liver is ramping up its ability to process bilirubin (the pigment that causes jaundice). Fat stores, particularly the specialized brown fat that helps a newborn regulate body temperature, are still being laid down.
Missing this window doesn’t necessarily cause permanent harm, but it does mean late preterm babies arrive less equipped to handle life outside the womb. Their systems work, just not as efficiently, and that gap creates a predictable pattern of short-term complications.
Breathing Problems
Respiratory issues are the most common reason late preterm infants need extra medical support. At 34 weeks, about 10.5% of newborns develop respiratory distress syndrome, compared to just 0.3% of babies born at 38 weeks. Transient tachypnea, a condition where fluid in the lungs clears slowly and causes fast, labored breathing for hours to days, affects 6.4% of babies born at 34 weeks versus 0.4% at 38 weeks.
Most of these breathing issues resolve on their own or with relatively brief treatment, but they can extend the hospital stay and require monitoring in a special care nursery.
Jaundice, Feeding, and Temperature
Jaundice is more common and more likely to become severe in late preterm infants. Their livers are less efficient at clearing bilirubin from the blood, and their tendency to feed poorly compounds the problem, since frequent feeding helps flush bilirubin through the digestive system. Hospitals typically check bilirubin levels at 24 hours and again before discharge.
Feeding difficulties are one of the less visible but most persistent challenges. Late preterm babies often have weaker sucking reflexes and tire easily during feedings, whether breast or bottle. They may fall asleep mid-feed, take in too little milk, and lose more weight than expected. Guidelines recommend that a breastfeeding specialist assess the baby at least twice before the family goes home, because what looks like adequate feeding in the hospital can deteriorate once parents are on their own.
Temperature instability is the third piece of the puzzle. Late preterm infants have less brown fat for generating heat and less white fat for insulation, paired with a higher surface-area-to-mass ratio that causes them to lose heat faster. They may need skin-to-skin contact, extra blankets, or time in a warmer to stay in a safe temperature range.
What Happens in the Hospital
Late preterm babies generally stay in the hospital longer than full-term newborns. Multidisciplinary guidelines recommend delaying discharge until the baby is at least 48 hours old. Before going home, the infant needs to demonstrate stability across several markers for at least 24 hours: successful feeding without excessive weight loss, stable vital signs for at least 12 hours in an open crib, adequate wet and dirty diapers, and no signs of infection.
A hearing screen is performed before discharge, along with the standard newborn screening blood test, which should be done at least 24 hours after feeding begins. Many hospitals also perform a car seat tolerance test, where a nurse monitors the baby in the family’s car seat for 90 minutes to make sure the semi-reclined position doesn’t cause drops in oxygen levels or heart rate. Some late preterm infants fail this test and need alternative positioning for travel.
A follow-up visit with a pediatrician is typically scheduled for 24 to 48 hours after discharge, primarily to recheck bilirubin levels and assess feeding. This early check-in is important because late preterm babies are at higher risk of being readmitted to the hospital, most often for jaundice or dehydration from poor feeding.
Long-Term Development
Most late preterm children develop normally, but as a group they do show subtle differences that can surface during the school years. Research has identified a slightly higher rate of delays in reading, attention, memory, and motor skills compared to children born at full term. Some studies also report more difficulty with emotional and behavioral regulation, which can affect self-esteem and performance in school.
These differences are statistical trends across large populations, not guaranteed outcomes for any individual child. Nutrition in the early months appears to play a role. One study found that late preterm children who received primarily human milk in their early weeks showed cognitive scores comparable to full-term peers by school age, while those who received mostly formula scored lower on measures of perceptual organization. The effect was modest, but it suggests that the type of early nutrition may help close the developmental gap.
Safe Sleep Considerations
Late preterm infants carry a higher risk of sudden infant death syndrome (SIDS) than full-term babies. Shorter gestational age is a strong, independent risk factor for SIDS even after accounting for birth weight and other variables. This means standard safe sleep practices, placing the baby on their back on a firm, flat surface with no loose bedding, are especially important for this group. The risk decreases as the baby grows and matures, but it remains elevated compared to term infants through the first year.