"My wife Amber is so hot, I can't keep my hands off her... Here is to 2014!!! #4," Mariano tweeted along with a sonogram.
The pair, who met on Survivor: All-Stars in 2003, got engaged during the season's live finale when they were the last two competitors still fighting for the million-dollar prize (Amber won). The two wed in 2005. Rob won Survivor: Redemption Island in 2011 and the couple also competed together twice on The Amazing Race.