A new 13-tonne sculpture of a disabled artist eight months into her pregnancy will be unveiled today in Trafalgar Square.

Alison Lapper Pregnant, by artist Marc Quinn, will remain on the square's fourth plinth for 18 months.

Born with no arms and very short legs, Lapper grew up in a children's home when her family rejected her.

She survived an abusive relationship and became an independent artist known for her work exploring the beauty of her own naked body.

Quinn, who also uses his own body in his art, carved the nearly 12ft-tall portrait of Lapper from white Carrera marble in Pietrasanta, northern Italy.

The piece is a "modern tribute to femininity, disability and motherhood", Quinn said.

"It is so rare to see disability in everyday life - let alone naked, pregnant and proud.

"The sculpture makes the ultimate statement about disability: that it can be as beautiful and valid a form of being as any other."

London mayor Ken Livingstone will unveil the sculpture during a public ceremony in the square today.

"Alison Lapper Pregnant is a modern heroine - strong, formidable and full of hope," the mayor said.

"It is a work about courage, beauty and defiance, which both captures and represents all that is best about our great city."

The piece is one of two sculptures chosen to be displayed on the fourth plinth in the next three years.

In April 2007 the giant nude will be replaced by Thomas Schutte's Hotel for the Birds.

Sandy Nairne, chair of the group that chose the work from a shortlist of six, called it "one of the most important public art commissions in recent years".

She added: "Although crafted in the ancient quarries in Italy, Alison Lapper Pregnant is a sculpture for our own time which will be compelling for millions of people."