Smoking Leads to Deadly Pregnancies

Ectopic pregnancy risk rises with smoking

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) It's no surprise that smoking is harmful to a pregnant woman's fetus. But smoking can also increase the risk of a woman experiencing a dangerous kind of pregnancy in the first place.

A recent unpublished study presented at a fertility conference has found the mechanism that at least partly explains how smoking can raise the risk of a woman having an ectopic pregnancy.

"Quit smoking - it can cost a life."

In a study led by gynecologist Andrew Horne at the Medical Research Council Centre for Reproductive Health in Edinburgh, Scotland, laboratory experiments involving the cells from fallopian tubes revealed how nicotine components can cause problems that may lead to an ectopic pregnancy.

Ectopic pregnancy occurs when the sperm fertilizes the egg while it is still in one of the two fallopian tubes, the passage eggs use to travel from the ovaries to the uterus.

It occurs in up to 2 percent of all pregnancies and can be fatal if not detected early and treated with surgery or an injection of a drug called methotrexate.

In the experiments, Dr. Horne put two different amounts of cotinine, a product that's created when nicotine breaks down, in with some cells from a fallopian tube.

One dose was 40 ng/ml and another was 400 ng/ml

They found that the cotinine interacted with a gene called BAD in a way which is linked to killing cells. Basically, the production of BAD was decreasing in the fallopian cells - just as BAD production decreases in a uterus when it is preparing to allow an embryo to implant.

The researchers then recruited ten smoking women and ten non-smoking women who were not pregnant and tested their fallopian tubes during the luteal phase, which is the time after their body ovulates (releases an egg) until the end of their cycle.

They found a similar effect on the BAD genes in the smokers as they had seen in their laboratory experiment. They also found some irregularities on the surface of the fallopian cells in the smokers.

The fact that the gene BAD tends to be "turned off" in the fallopian tubes of smokers - just as it is in a uterus before implantation of an embryo - means that the fallopian tube's environment may be mimicking the environment of an egg-ready uterus.

An egg might feel as though it is in the uterus instead of the fallopian tube if the BAD gene is not turned "on" as much as it should be in the tubes.

"It appears that smoking reduces the production of genes such as BAD which are involved in the control of cell death and promote an environment in the fallopian tube which is attractive to the developing embryo," Dr. Horne said.

They concluded that their results suggested that smoking might change how quickly the cells die and are created in the fallopian tubes, which may lead to changes in the cells' structure and function.

"We believe that these changes may contribute to the development of ectopic pregnancy," they wrote.

In addition to explaining why smoking may be detrimental to women by raising the risk of ectopic pregnancy, the researchers hope that their findings may help these types of dangerous pregnancies to be identified sooner as well.

The study was presented July 3 at the 28th annual meeting of the European Society of Human Reproduction and Embryology in Istanbul.

Because the study has not yet been published in a peer-reviewed journal, its results should be regarded as preliminary and still require review by researchers in the field. No information was available regarding funding or disclosures.

Reviewed by: 
Review Date: 
July 5, 2012
Last Updated:
December 10, 2012