Methods for inhibiting the production of specific vasoconstrictive prostanoids, such as thromboxane and prostaglandin F.sub.2.alpha., through the addition of insulin like growth factor, particularly IGF-I or IGF-II, to human placental cells are disclosed. IGF-I is demonstrated to avoid affecting material and placental production of prostaglandin E, human chorionic gonadotropin, PGFM, and 6-keto-PGF1-alpha by placental cells. Improved methods for vasoregulation of vasoconstrictive diseases of pregnancy are also disclosed. Methods for treating hypertension with IGF-I are also described. Improved methods for inhibiting pre-term labor are also provided. Methods for inducing labor with agents that specifically inhibit insulin like growth factor are also disclosed. Such inhibitors of IGF-I include antibodies, antagonists of IGF-I, and metabolizing enzymes of IGF-I.