Pregnancy typically lasts 40 weeks, but premature babies, or “preemies,” are born before the 37th week.

The Centers for Disease Control and Prevention reported that in 2016, 1 in 10 babies in the United States were born too early. Though common, there are many complications associated with preterm births, including breathing/respiratory problems, anemia, heart defects, neurological conditions and feeding issues.

“The earlier a preterm infant is born, the greater the risks are,” said Patricia Ramsay, MD, Ph.D. Because of those risks, neonatal intensive care units (NICUs) are dedicated to caring for fragile, premature babies, as well as treating other sick and low birth weight infants.

Fetal development in the later weeks of pregnancy

The 28th week of pregnancy is the beginning of the third trimester and is an important period of growth.

During this time, the baby is in the final stages of organ development, acquiring body fat and muscle, and his or her central nervous system is maturing. The last few weeks of pregnancy are especially important for brain and respiratory system development, as well as gaining a healthy amount of weight.

Near week 30, babies gain about half a pound a week until birth.

Week 36 to week 40 may seem brief but can make a big difference in the baby’s physical development. Because the complications vary depending on how preterm the infant is, stages of prematurity vary.

  • Very preterm: born at less than 32 weeks
  • Moderately preterm: born between 32 and 34 weeks
  • Late preterm: born between 34 and 36 weeks

Most premature babies are born in the late preterm stage, which has a high survival rate. Even so, there are risks associated with any stage of prematurity.

“There is no preterm birth that can ensure a healthy baby,” Ramsay said. “Even late preterm infants are at risk for possible complications.”

Not all premature babies need to go to the NICU following birth, but many do.

“All small preterm infants younger than 35 weeks are admitted to the NICU for observation and treatment,” Ramsay said. “Some late preterm infants may not be admitted, however they’re the largest population of infants requiring re-hospitalization and extra attention from their pediatrician to avoid life-threatening complications.”

Causes of preterm birth

There often is no identifiable cause for a preterm birth, but there are many possible contributors.

Known risk factors include:

  • Pregnancy with twins, triplets or other multiples
  • Having a previous premature birth
  • Uterine or cervical abnormalities
  • Bleeding during pregnancy
  • High blood pressure during pregnancy
  • Age (teen mothers/mothers over 35 years old)
  • Use of tobacco, alcohol or other substances during pregnancy

Because there are so many potential causes of preterm birth, there’s no sure way to prevent it from occurring. “However, the No. 1 action a mother can take to prevent preterm birth is to get prenatal care,” Ramsay said.

What goes on in the NICU?

Caring for premature infants can be challenging and often requires the specialty-trained staff, advanced equipment and specific medications found in NICUs.

There are many reasons a baby might be sent to the NICU, including being born prematurely, having birth defects or having congenital infections. “The NICU treats newborns with any problem that interrupts the natural transition from intrauterine to extrauterine life,” Ramsay said.

The term “neonatal” typically refers to the first 28 days of an infant’s life, though the length of stay in an NICU can vary depending on the conditions being treated. Ramsay notes that some late preterm babies may only need to stay in the NICU for 5 to 14 days, but babies with a very low birth weight might stay for 90 days or more.

Unlike other infant care units, an NICU is able to provide 24/7 monitoring of vital signs and provide life support when necessary. They’re also equipped with devices that can support adequate breathing, blood pressure, blood sugar levels and more.

Preterm infants in the NICU often require different treatment methods to help overcome challenges that arise because of their small size. “The physiological limits of the immature body’s development —such as size, lack of brain maturation, lack of lung and gut development, fragile skin and the infant’s inability to tolerate touch and/or stimulation — are all issues the NICU is able to address,” Ramsay said.

NICU staff members work with parents to help them understand the special type of care their newborn requires. The more that parents participate, the better the outcome for the infant, Ramsay said.