Marissa Ayala opens up about being born to save her sister’s life

It was a controversial move. Californians Abe and Mary Ayala, desperate to save their leukemia-stricken 16-year-old daughter, Anissa, chose to have another baby in the hopes of raising a compatible bone-marrow donor.

"Baby farming" was the debate of the day. When baby Marissa was born, the sisters made the cover of TIME.

Twenty one years later, the baby born to save her sister's life is speaking out.

"People are entitled to their own opinions, but I am so glad that I am in this family," Marissa, now 21, told Meredith Vieira on TODAY. "I could not have asked for a better family, so I've never questioned it."

Marissa was conceived after her parents and older brother failed to be bone-marrow matches for ailing Anissa. A donor was found, but backed out.

Attempting to conceive a donor was not guaranteed to succeed. Abe had to have a vasectomy reversed. Mary was 42, and conception odds weren't in her favour. On top of all that, a new baby would only have a 23 per cent chance of being a match.

It was worth the risk. When Mary was seven months pregnant, she learned that baby Marissa was a match.

When Mary was 14 months old, she saved her sister's life. Anissa is now completely free of cancer.

The sisters are close, despite their significant age gap. Cancer bonded them, with both acknowledging the other as their reason for existence:

"Without her and her sickness, I would not be here," Marissa said. "And without me being a perfect match for my sister, she would not be here as well."

Anissa says that even if Marissa had failed to be a match, she would have been thankful her parents expanded their family at a difficult time.

"They were so focused on me, what was going to happen, and it was just time to take the focus off me. And when I found out it was a little girl, I was thrilled."