The News of the World says Giggs' sister-in-law - with whom the Manchester United star had an eight-year affair - has revealed that she aborted his baby weeks before marrying his brother Rhodri.
Natasha Giggs was given £500 by the cheating footballer towards the cost of the abortion.
She said: "Ryan told me straight off, 'You know there's only one option - a termination. We can't ruin everybody's life'.
"I was due to fly out to Las Vegas to marry Rhodri within weeks and I knew I couldn't possibly marry him while I was pregnant with his brother's baby."
The 28-year-old told the News Of The World: "Going through with the termination was horrendous. Even though I was with Rhodri and loved him, I had feelings for Ryan."
The new revelations followed allegations that Ryan Giggs offered his brother £250,000 in hush money to avoid further details about his love life.
A friend of Rhodri's is reported to have claimed: "The last thing Ryan wants is more sex secrets coming out.
"He's been through hell. He's not exactly rolling in cash, so £250,000 would be very useful."