Final answer:
An infant generally increases in length by about 50% over the birth length during the first year, with more rapid growth occurring in the first six months.
Step-by-step explanation:
An infant typically increases in length by approximately 50% over what it was at birth during the first year of life. During this period, which is called infancy, the body undergoes significant growth both in weight and in length. A well-nourished infant doubles in length and triples in weight by their first birthday.
Growth in length is most rapid in the first six months, with an average of 2.5 cm per month, decreasing slightly to about 1.2 cm per month in the second half of the year. Infancy is characterized by this rapid growth, which is faster than any other time in human development, including puberty. An infant increases in length by doubling its birth length by the end of the first year. During the first six months, infants grow about 2.5 cm (1.0 in.) per month, and during the second six months, they grow about 1.2 cm (0.5 in.) per month.