November 17 (HealthDay News) -- In research that might have implications for human reproduction, U.S. and Chinese scientists have found that cigarette smoke damages mouse eggs and embryos.

The study was designed to examine whether cigarette smoke causes oxidative stress, cell death and dysfunction, and the shortening of telomeres (DNA at the ends of chromosomes that protect them from degradation). Two groups of female mice were exposed to cigarette smoke or cigarette smoke condensate for four weeks and compared to a control group of mice.

The mice exposed to cigarette smoke or the condensate were more likely than the unexposed mice to show increased fragmentation and delayed fertilization, resulting in impaired embryo development, the study found.

The fragmented eggs also showed oxidative stress, and embryos from mice exposed to cigarette smoke or condensate for four weeks before fertilization were more likely to contain dead cells and altered expression of the protein Oct4, which plays an important role in the formation of viable blastocysts (a stage of embryonic development).

The association between cigarette smoke or condensate and embryo development was dependent on the length of exposure, the team noted. But even embryos exposed to smoke for as little as four days showed reduced telomere length in cells and decreased blastocyst development, suggesting that embryos may be more sensitive to smoke-induced oxidative stress than eggs, the researchers said.

The study was published in the November issue of the journal Fertility and Sterility.

"Here is even more evidence demonstrating the dreadful effects smoking has on reproductive tissues and function. While there are some data implying that the effects may not be permanent, every woman planning to become pregnant would be wise to quit smoking or, better yet, never start," Dr. William Gibbons, president-elect of the American Society for Reproductive Medicine, said in a society news release.

SOURCE: American Society for Reproductive Medicine, news release, Nov. 17, 2008