Uteroplacental insufficiency in the rat reduces maternal progesterone and impairs mammary function and pup milk intake, compromising postnatal growth. We determined whether progesterone administration to rat dams progesterone-deficient following uteroplacental insufficiency improves lactation and pup growth. Uteroplacental insufficiency (Restriction) or sham surgery (Control) was performed on day 18 of pregnancy in WKY rats. Pregnant dams were injected with progesterone or vehicle, and Control mothers with vehicle for three days and killed on day 20 of pregnancy or day 6 of lactation. Progesterone treatment in the Restricted group restored maternal progesterone with no effect on mammary Pgr mRNA expression. Uteroplacental insufficiency triggered early lactogenesis, with increased mammary Csn2, Lalba and Wap mRNA. Progesterone treatment following uteroplacental insufficiency increased mammary alveolar number and area. Pups from progesterone treated mothers had increased body weight when compared to Controls. Overall, maternal progesterone treatment following uteroplacental insufficiency improved postnatal growth by rescuing the mammary impairment.