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Oh, babies: Sarah Jessica Parker says her 6-month-old twin girls "are about as un-identical as twins can be."

On Tuesday's Late Show With David Letterman, she showed off a new photo of Marion and Tabitha, who were born in June with the help of a surrogate mother.

"They are physically, intellectually spiritually, geographically, politically, ideologically and religiously as different as two small 6-month olds could be," Parker, 44, said.

She added that her 7-year-old son James Wilkie is taking well to his role as big brother. "He's been very hospitable and he's amused by them occasionally," said Parker, who is wed to actor Matthew Broderick.

Parker couldn't help but gush about her twins Monday at the NYC premiere of her new comedy, Have You Heard About the Morgans?

Asked to name the best thing about having twins, she told, "That’s an impossible question to answer. You cannot put it into a little sound bite into a tiny tape recorder. It's amazing. It's the most perfectly overwhelming experience."

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Soon after the twins were born, Parker began filming Sex and the City 2.

"It’s a strain," she told Us of balancing work and motherhood. "But I'm not going to complain. We do the best we can like every other family. You juggle, you organize, you fail, you have triumphs. Most working mothers work much harder than I do and have far less help."

Despite the occasional obstacles, she said she wouldn't change a thing. Motherhood "is a total blessing," she told Us, "and we're thrilled."