A full term pregnancy is descibed as being a full 37 weeks. Between 34 and 37 full weeks is considered late pre-term. During those final weeks, the infant's internal organs, including the brain, lungs, intestines and liver are still growing.

The average weight of a full term newborn is between seven and eight pounds. Babies weighing between 3 pounds, 4 ounces and 5 pounds, 8 ounces are considered to be low birth weight. Any baby born weighing less than the 3 pounds, 4 ounces is considered to have a very low birthweight. The number of low birth weight babies in the United States has grown to 8.3 percent, mostly due to the increase in multiple births. Only 1.4 percent of newborn babies fit into the very low birthweight category. Only a small fraction of that small fraction go on to survive and thrive. Most have to deal with complications such as respiratory distress syndrome, bleeding in the brain, heart problems and/or necrotizing enterocolitis, which affects the intestines. Many problems are due to the internal organs not having time to fully develop in the womb.