On average, fetuses gain about pounds during the last trimester of pregnancy, which brings the average birth weight to about 7.5 pounds.

4.5

Explanation:

During the last trimester of pregnancy, the fetus gains the maximum weight compared to the entire time fo development. If the pregnancy occurs for a full term, there is an increase of up to 6 inches in the baby's total size and a gain of about 4.5 pounds and there is an increase in he baby's weight of about half a pound every week.As a result of this around 16% of the body fat is gained during this period.