There is no cure, only treatment, so some parents choose to end the pregnancy.

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They also said states could regulate abortion procedures in the interest of a woman's health or in protecting a potential human life starting at the end of the pregnancy's first trimester.

CNN: Before and after Roe v. Wade

Near to the end of pregnancy, it shortens in preparation for labour and delivery.

BBC: Clue to premature birth mystery

It says women should receive a vaccine for tetanus, diphtheria and pertussis, together known as Tdap, toward the end of pregnancy, or between 27 and 36 weeks' gestation.

WSJ: Panel Pushes Vaccine for Pregnant Women

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.

CNN: North Dakota governor signs law banning most abortions

The Roe opinion, written by Justice Harry Blackmun, asserted that the right to privacy extended to a women's decision on whether to end a pregnancy.

WSJ: Roe v Wade: After 40 years, deep divide is legacy