Smoking Increases the Risk of Ectopic Pregnancy

A new study suggests that cigarette smoke reduces the production of a Fallopian tube gene, which could help explain the link between smoking and ectopic pregnancy.

Researchers at the Medical Research Council (MRC, Edinburgh, United Kingdom) exposed cells from the Fallopian tube to a breakdown product of nicotine called cotinine. They then showed that cotinine had a negative effect on genes known to be associated with cell death (or apoptosis), and in particular with the BCL2-associated agonist of cell death (BAD) gene, which normally undergoes expression reduction in the cells of the uterus just before the embryo implants.

In a further study the researchers showed that BAD expression was reduced in the Fallopian tube of women who were smokers due exposure to cotinine, resulting in an environment similar to that of the uterus as it prepares for normal implantation of the embryo and early pregnancy, thus encouraging and allowing ectopic pregnancy to occur. The study was presented at the European Society of Human Reproduction and Embryology (ESHRE) annual meeting, held during July 2012 in Istanbul (Turkey).

“The research is exciting because it provides new scientific evidence to help understand why women who smoke are more likely to have ectopic pregnancies,” said study presenter and coauthor Andrew Horne, MD, of the MRC Center for Reproductive Health. “The information gained from this study can also be applied to other conditions caused by smoking, and could help us prevent or treat them better in the long term.”

Ectopic pregnancy occurs in up to 2% of all pregnancies, and is the most common cause of maternal death in early pregnancy. It transpires when the embryo implants outside the uterus and in the fallopian tube. Currently there is no way to prevent an ectopic pregnancy, and the condition must be treated by abdominal surgery or, when the ectopic is small and stable, by injection of methotrexate (MTX) to abort.

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Medical Research Council (MRC)