Lincoln Ryman and his brother Byron may be the same age, but they are definitely not the same size.

Twins Lincoln and Byron were born in Sydney on May 15 just minutes apart. However, Byron weighed in at 3.39 pounds (1.54 kilograms), while Lincoln was a tiny 1.17 pounds (530 grams).

During Nicole Ryman's pregnancy, the boys suffered a twin-to-twin transfusion. The new mom had to be induced at 29 weeks and was warned that smaller baby Lincoln may not survive.

However, since their birth, both boys have become little miracles - both gaining weight and preparing to be taken home.

While Lincoln, who was born minutes after Byron, will continue to be monitored in newborn intensive care at Sydney's Royal hospital, Byron will be home in time for Mother's Day on May 13.

Neonalist Dr Parag Mishra told AAP, "Lincoln initially had a lot of breathing problems and then he had a lot heart problems, so an operation was done while he was still about 500g(1.10lbs). Hopefully he'll soon start gaining weight much more quickly and get nearer and nearer his brother."

The new mother, Nicole, continued, "We've been on top of the world because we didn't think we were going to have them both. We've had a few scares along the way but they're pretty well going forward now and I know I'm going to be able to take them home. During the pregnancy the doctors would write (Lincoln) off. But he's a big boy now. They're both fighters."

Since birth, Byron has gained 2.2lbs (one kilogram) while Lincoln has become just .66lbs (300 grams) heavier.