The couple confirmed the news via Instagram, saying: "Delighted to announce we are expecting twins. Our hearts are full of love - we can’t wait to meet you."
Georgina shares daughter Alana, three, with Ronaldo, who is also father to Cristiano Jnr, 11, and twins Eva and Mateo, four.
Friday's (AEDT) Instagram post had generated more than 16.7million likes just three hours after going live.
Ronaldo has scored six goals in nine appearances in all competitions since joining United for the second time, arriving from Juventus at the end of the recent transfer window.
However, United's overall form has suffered in recent weeks, the Red Devils winning just three and losing five of their past nine games.
Last Monday's (AEDT) humiliating 5-0 home defeat to Liverpool in the Premier League means Ole Gunnar Solskjaer heads into the next match against Tottenham knowing another loss could spell the end of his time in charge.