The Plan B emergency contraceptive pill works by preventing ovulation or by blocking a potentially fertilized egg from becoming implanted in a woman's uterus, according to the drug's label.

WSJ: Corrections & Amplifications

The drug works by using high doses of the female hormone progestin, which also is contained in birth-control pills, to prevent ovulation or block a potentially fertilized egg from becoming implanted in a woman's uterus, according to the drug's label.

WSJ: Judge Eases Restrictions on Plan B Emergency Contraceptive

The cause of pre-eclampsia is unknown, but it is clear that the placenta fails to invade into the wall of the mother's uterus.

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In the cloning experiment, cells from an infertile father would be injected into an egg, which is then implanted in the mother's uterus for the pregnancy.

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The drug works by using high doses of the female hormone progestin, which also is contained in birth-control pills, to block a potentially fertilized egg from becoming implanted in a woman's uterus.

WSJ: Judge Eases Restrictions on Plan B Emergency Contraceptive

The mother's abdomen and uterus are opened so as not to harm the placenta, which nourishes the fetus.

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If thawed semen is used, it has to be injected directly into the uterus through the ewe's belly wall, which requires a local anaesthetic and also large quantities of defrosted semen.

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She said the result was in clear contrast to the Women's Health Institute trial of combined progestogen and oestrogen therapy in women with a uterus.

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"As the uterus grows and pushes the diaphragm up, there is less room for the lungs, " affecting a woman's ability to breathe, she said.

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