The fetus can now be called a miniature adult. At farrowing, about half are born tail first and half are born head first. Embryos which die before day 35-40 are usually reabsorbed by the dam. However, progressive calcification of the skeleton begins to occur from day 36 onward and deaths occurring after this point will result in mummification. By day 109 the fetus weighs about 1 to 2 pounds.
Hair shafts begin to emerge but remain trapped under a skin layer until close to birth.
Throughout gestation, the uterus gradually enlarges from about 2 to 3 pounds at mating to up to 60 pounds, including fetal contents, during the last week. The average gestation length or time from conception until farrowing is 114 days. During gestation, the piglet grows from the union of a microscopic sperm and ovum into a fully formed individual weighing from 3 to 3 pounds.