PARIS – Maybe they should call it the “Mama Lisa.” Researchers studying 3-D images of the “Mona Lisa” say she was probably either pregnant or had just given birth when she sat for Leonardo da Vinci’s 16th-century masterpiece. The clue was something she wore.

Scans turned up evidence of a fine, gauzy veil around Mona Lisa’s shoulders – a garment women of the Italian Renaissance wore when they were expecting, a leading French museum researcher, Michel Menu, told The Associated Press in an interview Wednesday.

As the painting aged, the veil darkened. The thick, dark varnish on the work made it hard even to know what color her dress is – it has been described as everything from black to brown to green. A piece of fabric draped over Mona Lisa’s shoulder was sometimes interpreted as a shawl or a scarf.

But images obtained from infrared reflectography tell a different story. The veil – called a guarnello – is transparent, and it looks similar to a gauzy garment in Sandro Botticelli’s “Portrait of a Lady,” depicting a pregnant woman with her hand over her stomach.

Tradition holds that the “Mona Lisa” is a painting of Lisa Gherardini, wife of Florentine merchant Francesco del Giocondo, and that Leonardo started painting it in 1503. In France, the painting, on display at the Louvre Museum, is referred to as La Joconde – the French version of her married name. The name Mona Lisa is the equivalent of “Madam Lisa.”

The veil “would confirm art historians’ hypothesis that Giocondo asked for a painting of his wife to celebrate the birth of his second son,” said Menu, chief of the research department at the French Museums’ Center for Research and Restoration, which has its offices in the Louvre.

The scans also make clear that Mona Lisa does not have her hair down, as it appears. Most of her tresses are pinned back into a chignon and covered with a veil, Menu said. The analyses of hairstyle and clothes were made by Bruno Mottin, curator of the research department at the center.

Various high-grade scans were taken over three sessions in October 2004, on days when the Louvre was closed, sometimes overnight.

The scans have been collected in a book, “Mona Lisa: Inside the Painting,” published this month by Harry N. Abrams, Inc. Menu and Mottin wrote the book with another leading French researcher, Jean-Pierre Mohen.

Teams from the National Research Council of Canada analyzed the painting with three-dimensional digitization through laser scanner technology. The scans revealed depth resolution so detailed it was possible to see differences in the height around the paint surface cracks and in the thickness of the varnish.

“We know how the painting is painted with very thin layers,” Mottin told reporters in Ottawa, Canada. “That’s one of the things we couldn’t see by the naked eye, and that Canadian technology brought us.”

John Taylor of Canada’s National Research Council said there were no signs of brush strokes. “That includes the very fine details of the embroidery on the dress, the hair,” he said. “This is the ‘je ne sais quoi’ of Leonardo. The genius. We don’t know how he applied it.”

The data show warping in the poplar panel Leonardo used as his canvas, but the painting is in relatively good shape.

“We didn’t see any sign of paint lifting,” Taylor said. “So for a 500-year-old painting it’s very good news. And if they continue to keep it the way they have in an environment-controlled chamber, it could remain like that for a very long time.”

Canadian scientist Marc Rioux said the data would be studied for many years to come, providing more insights into Leonardo’s painting.

“We’ve barely scratched the surface of the data available. Scientists now have access to a virtual copy. I would say this is the most important achievement of the project,” said Rioux of Canada’s National Research Council. “There will be a lot more information about that painting just because there are many more scientists looking at the data.”

“What is amazing and paradoxical about that painting is that people think it’s been analyzed but it’s exactly the opposite,” Rioux added. “This is the most inaccessible painting in the world. Why? Because it’s 99.9 percent of the time in the Louvre for the public to view. The last time it was up for examination was 1952.”

Mona Lisa’s smile has for centuries inspired speculation. In the 1950s, Nat King Cole asked in a song lyric if she was smiling to “tempt a lover” or “to hide a broken heart?”

No scientific research will ever figure out exactly what Leonardo was trying to convey, or why exactly she was smiling.

New discoveries “don’t take away the mystery,” Menu said. “On the contrary, they merely add another layer to the meaning, which only makes things more interesting.”