Get the height value of a parent form

I have a mdi form and a child form. i want to adjust the height and width of the child form based on that of the parent form

I am putting code:

me.height = me.parentform.height

I do this during the form load procedure of the child form.

Unfortunately me.parentform.height = nothing at this time.

how can i get  the hieght of the parent form?

Anthony