Bristol Palin says becoming pregnant as a teen gave her purpose.

The 27-year-old former "Bristol Palin: Life's a Tripp" star said in an Instagram post Wednesday that her children, 9-year-old son Tripp, 2-year-old daughter Sailor Grace and 1-year-old daughter Atlee Bay, have been the "biggest blessing" in her life.

"10 years ago this week - my life took the biggest possible turn.. I was 17 and a junior in high school," Palin recalled of learning she was pregnant with Tripp.

"It took hearing your heartbeat for a positive pregnancy test to really mean anything to me.. and took holding you in my arms to realize my life was going to be changed forever," she said.

"I am so thankful for God's plan over our life, and His grace that has covered us entirely.. my kids truly are my biggest blessing #purpose," the star added.

Palin is parent to Tripp with Levi Johnston and to Sailor and Atlee with her estranged husband, Dakota Meyer. She shared a photo Tuesday with her three children while celebrating Atlee's first birthday.

"#1," she captioned the picture.

Palin and Meyer celebrated Easter as a family in April following news Meyer filed for divorce in January after less than two years of marriage.

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Meyer cited "discord or conflict of personalities" as the reason for the split.

Palin is the eldest daughter of former Alaska governor Sarah Palin. She will serve as maid of honor in her sister Willow Palin's upcoming wedding to Ricky Bailey.