Breast Implant and Weight
It really depends on your height here. As other surgeons have mentioned here, if your height is in the 5 feet range then you are very low weight for your height, and you have other issues that need to be addressed.
But the weight per se is not the determining factor.
Breast augmentation with very low body weight
Seventy pounds is obviously a very low weight for an adult; unless your height is well-below 5 feet tall, I'm very concerned about your nutritional status. I'd be very concerned about the results of breast augmentation at your current weight. First, given that you are probably quite malnourished, the possibility of significant complications is much greater. Second, from a strictly aesthetic perspective, your lack of tissue support makes you prone to complications such as implant malposition or migration, and possibly even capsular contracture.
Before you seek consultation with a plastic surgeon, your best bet is to see your medical doctor. He or she can assess your nutritional status and help optimize it prior to even considering surgery.
Best of luck.
Breast augmentation for a 70 pound person?
If you are an adult and if you are of normal height, you are severly malnurished and may well have an eating disorder. These circumdstances would not go along with a safe breast augmentation. Please see a doctor for a thorough evaluation.
Your weignt is not that important in this consideration, especially withouth your height, chest size in inches, etc. Implant selection is based on many factors and especially the diameter of the implant, your chest wall, and your desires, but other things as well.
Breast augmentation at 70 pounds.
You did not give your height. So this is incomplete information. If you 4 feet 5", 70 pounds may be a reasonable weight. However, if you are 5'4', you are potentially malnourished and may suffer from an increased rate of complications.
You need a medical and nutritional evaluation
Breast augmentation does not have a limit (upper or lower) on weight. However, an adult body weight of 70 pounds could indicate that there are some nutritional issues that could affect your healing. You would be best served by having your primary physician evaluate you from a medical standpoint and nutritional standpoint. Best of luck.
Breast implants in a small-framed person
There is no weight requirement for breast augmentation. Provided you are older than 18, you are eligible for the procedure. The implants come in a variety of shapes and sizes, and the implant for your frame would certainly be one of the smallest sizes.
Please consult with a board certified plastic surgeon regarding your particular anatomy and the best implant size for your petite frame.