From HP2030:

Infants born before 37 weeks of gestation have a higher risk of infections, developmental problems, breathing problems, and even death. Preterm births are more common in some racial/ethnic groups. Strategies to reduce preterm births include promoting adequate birth spacing, helping women quit smoking, and providing high-quality medical care for women during pregnancy.

Low birthweight infants (weighing less than 2,500 grams at birth) are at increased risk of infant mortality and a host of short- and long-term complications. There are two categories of low birthweight infants: moderately low birthweight infants (between 1,500 and 2,499 grams at birth) and very low birthweight infants (less than 1,500 grams at birth). Very low birthweight infants account for the majority of differences seen in health outcomes between low birthweight and normal weight infants. 

Possible health conditions affecting infants born with low birthweight include heart problems, breathing problems, bleeding in the brain, intestinal disorders and retinopathy. Health conditions that may affect children and adults born with low birthweight later in life include Type 2 diabetes, heart disease, high blood pressure, obesity, cerebral palsy, and learning and behavioral problems.

The average hospital cost for a low birthweight infant is estimated to be $27,200 and $76,700 for a very low birthweight infant, compared with $3,200 for a normal weight newborn. Very low birthweight infant care accounts for 30% of all newborn health care costs, with an annual cost of approximately $13.4 billion in neonatal intensive care unit hospitalizations. Low birthweight and very low birthweight infants who survive to adulthood often experience serious physical and mental morbidities, significantly increasing the costs of hospitalization throughout their lifespan.

Prematurity occurs when a baby is born before the 37th week of the pregnancy. A normal pregnancy lasts for 40 weeks. Premature babies are more likely to have serious health problems, because their internal organs, such as their lungs or brains, have not fully developed. So, they may have problems breathing or have bleeding in their brains, which is like a stroke. Premature babies are often very small and have low birth weight.