As you probably know, pregnancy will cause your breasts to become larger, due to hormonal changes and your body's preparation to lactate, or produce milk.
Breast augmentation should not affect your body's ability to produce milk, but your long-term aesthetic results may be affected.
Regardless of breast implant or the incision that the implant is placed, breast augmentation should not affect your body's ability to lactate or produce milk.
So, a saline or silicone implant should not a difference in your body's ability to lactate.
The same goes for above or below muscle placement of your implant, and whether your implant was placed with a breast fold, areolar, or under arm incision.
Your long-term aesthetic result from a breast augmentation may be compromised with pregnancy.
Time and gravity will cause your breasts to sag or drop.
If you gain and lose a lot weight, then your breasts may also sag prematurely.
Certain medical conditions, especially smoking and tanning excessively, may also cause your skin to thin out and cause early breast sag as well.
Pregnancy will cause your breasts to enlarge and then potentially sag, and multiple pregnancies will probably induce more of this as well.
It is impossible to predict how much your breasts may sag, or even if they will sag at all, but it is possible that it may happen.
Prevention is controversial, because a statistically significant study regarding prevention of breast sag has not been completed.
There are some recommendations, including wearing an excellent support bra during your pregnancy as well as afterwards, which may help.
Wearing a bra more often, essentially 24 hours, may help as well.
If your breast sag is significant, then you may need a breast lift.
Although it can be done at any time, generally most women prefer to have a breast lift after they are done breastfeeding and having children.
A breast lift is an out-patient procedure, and can be safely done with your current breast implants, or with a change in breast implant size or filler material.