Bristol Palin, who launched an abstinence campaign after giving birth as an unwed teenage mother, announced she is pregnant with her second child out-of-wedlock.
The disclosure came a month after her wedding with Medal of Honour winner Dakota Meyer was called off.
Ms Palin, the daughter of 2008 Republican vice presidential candidate and former Alaska Governor Sarah Palin, directed Twitter followers and Facebook friends to her blog, where she announced the pregnancy.
"I know this has been, and will be, a huge disappointment to my family, to my close friends, and to many of you," the 24-year-old wrote, before asking for privacy for her and her son Tripp.
"I do not want any lectures and I do not want any sympathy," she said.
Ms Palin was 18 when her mother was selected by Senator John McCain to be his running mate in the 2008 presidential election. Shortly after the selection, it was announced that Bristol was pregnant.
Sarah Palin said Bristol and the baby's father, later revealed to be Levi Johnston, would marry, but the couple eventually ended the relationship.
Bristol Palin later became a paid spokeswoman advocating abstinence and warning against teenage pregnancies. She twice performed on Dancing With The Stars and had a short-lived cable television show, Life's A Tripp.