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An abortion is a procedure to end a pregnancy. It’s also sometimes known as a termination of pregnancy. The pregnancy is ended either by taking medicines or having a surgical procedure.

Most abortions in England, Wales and Scotland are carried out before 24 weeks of pregnancy. They can be carried out after 24 weeks in very limited circumstances – for example, if the mother’s life is at risk or the child would be born with a severe disability.

In France, medical abortion can take place until the end of the 5th week of pregnancy and surgical abortion is allowed until the end of the 12th week of pregnancy.

Overview of abortion

U.S. Abortion statistics

Physiology of Pregnancy and Site of Action of Drugs Used to Terminate Pregnancy.

After progesterone binds to its receptor, the complex forms a dimer and binds to a segment of the promoter region of different target genes. This genomic effect leads to changes in the structure of epithelial-cell membranes and in the synthesis of implantation proteins. Progesterone decreases uterine contraction, probably by a genomic effect. In contrast, during labor, oxytocin and prostaglandins induce uterine contraction. They bind to their respective receptors, resulting in increased phospholipase C activity and increased intracellular concentrations of inositol triphosphate (IP 3) and calcium. The released calcium interacts with myosin light-chain kinase on the contractile filaments to cause uterine contraction. In addition, progesterone may have a nongenomic action by binding to the oxytocin receptor and inhibiting the action of oxytocin or by other mechanisms, including the nitrous oxide system. During a normal pregnancy (right-hand panel), the blastocyst attaches to the receptive endometrium, or decidua, on day 6 or 7 after ovulation. The trophoblast then traverses adjacent cells and invades the endometrial stroma.

The agents used to terminate pregnancy (left-hand panel) are methotrexate, which inhibits trophoblast division; prostaglandins, which increase muscle contraction; and epostane, which decreases progesterone synthesis. Mifepristone, a progesterone antagonist, blocks the binding of progesterone to its receptor, amplifies the action of prostaglandins on the myometrium, and induces cervical softening. ER denotes endoplasmic reticulum, and mRNA messenger RNA. The broken arrows indicate inhibitory or blocking actions.