Is Areolae Reduction Good 3 Years Before Getting Pregnant?

Ultimately, this depends on how much it bothers you. If this is a source of distress, the surgery is relatively low risk but you should be prepared to revise the surgery once you have completed nursing.

Yes it is fine to have areola reduction three years prior to pregnancy. However it is important that you understand that future pregnancy and breastfeeding can impact your results. Often times the surgery can be revised if necessary after you are finished having children.

If you're significantly unhappy with the size of the areolae, you could have them reduced now. However, the possibility that pregnancy will re-stretch the areolae and that additional surgery will be required afterwards cannot be discounted. This is a personal choice but my inclination would be to wait if you are certain that you will have a a child in the next three years and to proceed if having children is conjectural and not a certainty in your life.

If you're just looking for areolar reduction (making the dark circle around the nipples smaller), there's no reason not to go ahead and have it done if it really bothers you. You'll have 3 more years to enjoy your new breasts before pregnancy changes them. You cannot predict exactly how pregnancy will change a breast, so you may or may not need to touch up that areolar reduction after pregnancy.

Probably not.
An areolar reduction can be done by itself or as part of either a Breast Lift (Mastopexy) or a Breast Reduction (read link below to understand similarities and differences). With Pregnancy the breast will grow and stretch the entire skin envelope, including the areola. Any tightening of the areola and or of the skin envelope will be affected - the areola will be stretched as will be the skin envelope.
Dr. P. Aldea

In my opinion, this would not be a good idea.  Isolated areola reduction without a lift or reduction of the entire breast is exceptionally rare anyway.  I think whatever you might gain would potentially lost be the stretching of the breasts during pregnancy or breast feeding.