Women who smoke regularly are four times more likely to have ectopic pregnancy than those who don't smoke, say scientists. Researchers of the Edinburgh University have found a chemical in cigarette smoke that causes a reaction, which may lead to ectopic pregnancies.

The researchers said Cotinine triggered a reaction, which increased a protein in the Fallopian tubes. The protein, called PROKR1, raised the risk of an egg implanting outside the womb.

PROKR1 allows pregnancies to implant correctly inside the womb, but its presence in the Fallopian tubes is believed to increase the risks of this happening outside the womb.

The study found that women who smoked and developed an ectopic pregnancy had twice as much PROKR1 in their Fallopian tubes as women who did not smoke and had previously had a healthy pregnancy.

Researchers believe that too much of the protein prevents the muscles in the walls of the Fallopian tubes from contracting, which in turn hinders the transfer of the egg to the womb.

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