A twin saved her sister's life while still in the womb, by sending out distress signals prompting doctors to deliver them early-which turned out to be critical for the other twin's survival.

Preemie Poppy McBride's heart rate began to waver on the monitor at 31 weeks and five days into the pregnancy, which doctors say forced them to deliver her and her twin, Winnie.

Despite being the smaller of the twins-at 1lb 11oz-Poppy was perfectly healthy, and nothing was wrong with her heart.

Doctors had never been concerned about her sister, Winnie-who weighed more than three times that of Poppy. But, at 3lbs 8oz, she emerged with underdeveloped lungs and was whisked into the intensive care unit.

The mother, Leah McBride, says she was told by doctors that Poppy saved her sister's life and if they had waited any longer to deliver the twins, Winnie would not have made it.

She still had to have surgery at 14 days old to relieve a build-up of fluid on her brain, but has since recovered fully.

"Our doctors told us, ‘I think your tiny twin saved her sister's life,'" said the stay-at-home mom from Lake Jackson, Texas. "Poppy's heart rate had been all over the place, so they had to deliver, but when she was born, she was completely fine."

"They think she was sending out distress signals because she knew her sister wouldn't survive if they weren't delivered then.

"Even now Poppy takes care of Winnie, though she is still much smaller," said the 28-year-old mom.

"Doctors said she was feisty, but she was smaller than a little elf on the shelf."

Now both twins have nothing wrong with them, and they're the best of friends and thriving.

"They are as smart as can be," Leah said. "Winnie is smarter than average. She can read books from memory at three."

"I tried to move their beds apart recently and they weren't having it. They are so close."

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