新托福阅读材料：孕妇戒烟未必能停止对婴儿的不良影响

会计考友

吸烟是危害人们健康的一大元凶，而对于一些女性烟民来说，吸烟会给她们的后代产生许多不良甚至致命影响。有些人认为妇女怀孕后戒烟就能停止对腹中婴儿的伤害，但是最新一项研究结果可能要让这些人失望了。  
　　Cigarette smoke plays an undisputed role in the development of lung and other cancers. Carcinogens in the smoke damage DNA, which often results in mutations in genes that promote the development of cancer. It's also well known that second-hand smoke can have effects indistinguishable from active smoking. While maternal tobacco smoking has been associated with low birth-weight, premature delivery and brain and lung defects, only a few studies have found evidence of genetic mutations in newborns resulting from exposure to tobacco smoke while in the womb.

- s6 w% G& {" c　　A new study by Stephen Grant, professor of environmental and occupational health at the University of Pittsburgh, confirms that both active smoking and passive exposure to second-hand smoke in pregnant women lead to genetic damage in the newborn. Importantly, the research shows that there was a similar frequency of mutations among smoking mothers, those exposed to second-hand smoke, and moms-to-be that quit smoking after they learned of their pregnancy. The authors conclude that quitting smoking during pregnancy without actively avoiding exposure to second-hand smoke may not protect the developing fetus. The results were published online June 30 in the Open Pediatric Medicine Journal.
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　　"These findings back up our previous conclusion that passive, or secondary, smoke causes permanent genetic damage in newborns that is very similar to the damage caused by active smoking," Grant said in a prepared statement.

　　Grant looked for mutations in the gene known as GPA in red blood cells collected from the cord blood of babies born to mothers exposed to smoke. The results are in agreement with previous studies that analyzed white blood cells from newborn cord blood for mutations in HPRT, a different gene commonly used as a biomarker for exposure to carcinogens. Those studies also documented a correlation between maternal exposure to both primary and second-hand smoke and increases in the frequency of HPRT mutations.

9 B+ ~! V4 U* ?0 k; U　　"By using a different assay, we were able to pick up a completely distinct yet equally important type of genetic mutation that is likely to persist throughout a child's lifetime," Grant said. He concluded that the assays for mutations in either gene should be considered complementary tests, reflecting mutations that occur through different mechanisms.

　　"Pregnant women should not only stop smoking, but be aware of their exposure to tobacco smoke from other family members, work and social situations," Grant said.