Much of an infant's brain growth occurs during the last half of pregnancy, and the risks of premature birth vary depending on how soon a baby is born. Researchers at McMaster University say the last two months in the womb are critical to correct development of the brain. According to Brigham and Women's Hospital, an affiliate of Harvard Medical School, "The brain of premature babies may not always develop as well as those who are carried to full term."
Premature Birth Defined
Preterm labor is that which begins prior to the completion of 37 weeks of pregnancy, and its causes are not fully understood. More than 70 percent of premature babies are born between 34 and 36 weeks gestation, and most are the result of spontaneous preterm labor or rupture of the amniotic sac that holds the baby. According to the National Vital Statistics Reports of January 2008, the rate of premature birth has increased by 36 percent since the early 1980s.
Infant Brain Growth
According to the December 2005-January 2006 issue of MIT's Technology Review, neurons in the head of the fetus originate as a mass near the center of what will become the brain. These, and the glial cells which assist communication among neurons, experience rapid growth while seeking connections with other cells. Billions of connections are made during the last weeks of pregnancy, during which time the brain is "massively overdeveloped, with far too many wires and connections." This is when the brain begins paring back as if it were testing the value of each connection, retaining some and trimming others, to produce a "sleek, efficient machine."
The MIT Review says premature birth likely disrupts the migration of nerve cells, the growth of glial cells and the brain's testing and trimming of them. "Premature kids have most of the neurons they will carry with them into adult life," the Review continues, "but it's possible they're not in the right places or properly connected or tested." According to Columbia University psychiatrist Bradley Peterson, researchers are "intensively testing" these possibilities.
Outside the Womb
Dr. Sandra Witelson, who led a McMaster University study of babies born after only 26 weeks of gestation, said ultrasound readings indicated that normal early development of the infant brain "may be compromised when it takes place outside of the womb." In the womb, the infant is bathed in fluid; few sounds are audible and eyelids are closed. "Very little patterned sensory stimulation reaches the brain," Witelson said. Upon birth, however, the premature infant is suddenly immersed in sights, sounds and touches. According to Witelson, research suggests that "stimulation of the brain while it is still under construction may not be beneficial."
The Clinic View
According to the Mayo Clinic, among the brain complications a premature infant may encounter are intra-cranial hemorrhage, cerebral palsy and other neurological problems, developmental delays and learning disabilities. Some difficulties may not arise until later in childhood or even adulthood. Sub-par performance in school is often of prime concern. The Mayo Clinic emphasizes, however, that not all premature babies encounter medical or developmental problems. "By 28 to 30 weeks, the risk of serious complications is much lower. And for babies born between 32 and 36 weeks, most medical problems related to premature birth are short term."