Hi, I am 27 years old and have had implants (325cc hp). I want to reduce them to 200cc. Should I wait after having children?

The results of the breast revision may be compromised if it is done before pregnancy. Many women undergo breast procedures to restore their breasts to the way they looked prior to pregnancy.  Therefore, if you experience weight gain, pregnancies, or any other drastic body altering changes, it is very possible the results may be compromised.  Hence, it may be best to delay your procedure(s) involving the areas affected by pregnancy, weight gain and nursing until after your final pregnancy if at all possible or predictable.

If your breasts change significantly with pregnancy, and especially if you breast feed, you may lose a lot of the nice appearance of your breasts.  I'd do surgery now only if you are having problems with your oversized breasts now.

Unless you have significant concerns about your breasts now, or think you will during pregnancy, I would advise you to wait on undergoing any further elective breast surgery until you have completed pregnancies. Doing so will help minimize  the number of operations you undergo.   You may find the attached link, dedicated to revisionary breast surgery (specifically downsizing) helpful to you as you learn more. Best wishes.