Some states have no time limit, while others allow abortion up to the end of the second trimester, about 27 or 28 weeks into the pregnancy.

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To get human retinal cells at the same stage of development, however, would involve taking stem cells from a foetus during the second trimester of pregnancy.

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It usually ends by the second trimester.

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The procedure -- called "partial birth abortion" by its critics -- is typically performed in the middle-to-late second trimester.

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Gosnell also was accused in the death of Karnamaya Mongar, 41, who died of an anesthetic overdose during a second-trimester abortion at his West Philadelphia clinic.

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Gosnell originally faced eight counts of murder in the deaths of seven babies and Mongar, 41, who died of an anesthetic overdose during a second-trimester abortion.

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