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Updated November 25, 2014.

What is a Late Preterm Infant?

Late preterm infants -- babies born between 34 and 37 weeks gestation -- look like smaller versions of full term babies. For a long time, late preterm babies were treated like full term babies. However, research has increasingly shown that these babies are not the same as full term infants, and that they have a unique set of needs and challenges. Babies born close to term are, in fact, preemies.


Even after 37 weeks gestation, full term infants may have some of the same problems as late preterm babies. The risk of health problems due to prematurity starts to decline around 37 weeks, but doesn't level off completely until 39 weeks gestation.

Immediate Health Concerns

In the hours after birth, babies face several challenges as they adjust to life outside the uterus. Breathing air, staying warm, and getting used to the world are all hard work! Although many late preterm babies adjust just fine, some have trouble. Even late preterm babies born to healthy moms with no complications may face:

• Respiratory problems: Respiratory problems occur in 4.2% of late preterm births, but only 0.1% of full term births. Respiratory problems may be mild or severe, and may include respiratory distress syndrome, transient tachypnea of the newborn, pulmonary hypertension, and the need for respiratory support.
• Hypoglycemia: While only 0.4% of term babies suffer from low blood sugar in the hours after birth, 6.8% of late preterm babies are hypoglycemic after delivery. Babies who are born early have not stored as much sugar as full term babies, and become hypoglyemic easily when they are cold or stressed.

• Poor thermoregulation: Preterm babies don't have as much stored fat as term babies have, and they get cold easily. Cold babies burn more calories to try to stay warm, making hypoglyemia worse and slowing weight gain.

Concerns in the First Weeks

Even after late preterm babies make the initial adjustment to life outside the womb, they still face challenges. These challenges lead to a high rate of hospital readmission in late preterm babies who are discharged within 48 hours of birth. Parents and pediatricians caring for late preterm babies need to be careful to make sure that these fragile babies stay healthy after they go home.

• Jaundice: Although only 2.5% of full term babies have jaundice serious enough to need phototherapy, 18% of late preterm babies have jaundice bad enough that it must be treated.
• Feeding challenges: Late preterm babies get tired easily and may not be strong enough feeders to drink enough breastmilk or formula to gain weight. This can cause dehydration or failure to thrive. Breastfeeding failure is another risk: moms whose babies do not breastfeed effectively may not produce enough milk to feed their babies.
• Sepsis: Because their immune systems are not fully developed, late preterm infants have a greater risk of infection than term babies. They are more likely to have bloodwork drawn to test for infection and are more likely to require antibiotic therapy.

Further Concerns

Many of the problems that late preterm babies face are known to impact brain development. Unfortunately, most studies of long-term neurodevelopmental outcomes in premature babies have focused on babies born before 34 weeks. We do know that late preterm babies are at risk for developmental delay, and more research is being done to see how late preterm babies do in school as they grow older. Nonetheless, with good care, the majority of these infants are likely to do just fine.

<sub>Darcy, A. MSN, RN. "Complications of the Late Preterm Infant." The Journal of Perinatal & Neonatal Nursing January/March 2009. 23;78-86.

Melamed, N. MD, Klinger, G. MD, Tenebaurm-Gavish, K. MD, Herscovici, T. MD, Linder, N., Hod, M. MD, Yogev, Y. MD. "Short-Term Neonatal Outcome in Low-Risk, Spontaneous, Singleton, Late Preterm Deliveries." Obstetrics & Gynecology August 2009. 114; 253-260.</sub>