二手菸對孕婦的危害眾所周知，尤其在妊娠晚期最明顯，但國際最新研究顯示，儘管排除母體接觸二手菸害的可能性，婦女於懷孕前所吸入的二手菸物質，仍有可能影響懷孕後胚胎的神經發展。
英國杜克大學全球健康研究所進行動物實驗，模擬人體吸入二手菸的情境，發現大鼠尚未懷孕時攝入的二手菸化學物質，會在整個妊娠時期影響胚胎的腦部發育，破壞大腦與學習、記憶和情緒反應有關的區塊。
這是學界第一個孕前二手煙影響的研究，發表於《毒物科學》期刊。
英國杜克大學藥學與癌症生物學教授斯洛特金（Theodore Slotkin）說：「這項發現對於公共衛生有重大意義，因為它顯示不只懷孕期間要避開二手菸，懷孕前甚至所有育齡婦女都應該避免吸二手菸。」
斯洛特金和研究團隊萃取出二手菸中的物質溶於溶液，透過植入於實驗動物體內的幫浦，分別在交配前、懷孕早期和懷孕晚期給予母鼠。
接著在後代剛成年後，針對過去研究指出尼古丁和二手菸會影響的大腦區域進行觀測。結果發現，三種時期給予二手菸溶液都會造成腦部膽鹼系統和血清素系統功能受損。膽鹼系統主宰學習和記憶，血清素系統影響情緒行為。
若動物實驗結果能推論到人體，育齡女性尚未懷孕時吸入的二手菸，也可能會影響未來胚胎的腦部發展。
二手菸是如何在懷孕前就能影響胚胎目前尚不清楚。研究人員表示需要更多研究進一步探討，但可能是因為部分二手菸物質會停留在體內一段時間。
研究人員也認為，二手菸可能改變母鼠的新陳代謝或內分泌，或是造成卵子外遺傳特性改變，進而影響控制大腦功能的基因。
同一組科學團隊過去也曾發現，二手菸害很大一部分是來自其中的尼古丁。研究認為電子菸對於育齡婦女也有相當程度的危害。
Women of childbearing age who inhale second-hand tobacco smoke even before conception may put their future babies at risk of impaired brain development, if the results of an animal study by scientists at Duke Health are found to apply to humans.
Using rats in experiments carefully designed to mimic the second-hand smoke exposures that humans encounter, this study is the first to show that exposure to second-hand smoke before conception is potentially damaging.
The researchers found that the chemical components of tobacco smoke affect fetal brain development throughout pregnancy.
The smoke exposure damages regions of the brain involved in learning, memory and emotional responses.
“This finding has important implications for public health, because it reinforces the need to avoid secondhand smoke exposure not only during pregnancy, but also in the period prior to conception, or generally for women of childbearing age,” said Theodore Slotkin, Ph.D., professor in Duke’s Department Pharmacology & Cancer Biology.
Although the impact of second-hand smoke was greatest with exposures occurring in late gestation, damage to the fetuses’ neuro-development was found even when the mothers were exposed only before conception.
Slotkin and colleagues, publishing in the January issue of the journal “Toxicological Sciences,” simulated secondhand smoke exposure by capturing and extracting the chemical compounds of tobacco smoke and administering the solution through implanted pumps in the laboratory animals.
Groups of female rats received the tobacco smoke extract during one of three periods: before mating, early gestation or late gestation.
The researchers then studied the offspring starting in early adolescence and into adulthood, focusing on brain regions that are known to be adversely affected by nicotine and tobacco smoke.
The researchers found that exposure to tobacco smoke extract in all three of the study periods resulted in the offspring having impaired function of the cholinergic brain circuits that govern learning and memory, and of the serotonin circuits that affect mood and emotional behavior.
It is not known how the smoke exposure damages fetal brain development prior to pregnancy. The researchers said more study is needed, but potential causes include the lingering effects of some of the smoke components, which can remain in the body for several days after exposure.
They also suggested that the chemicals might change the mother rat’s metabolism or hormonal status, or they could be causing an epigenetic alteration in the egg, which affects the activity of genes that control brain function.
An earlier study from the same team found a substantial portion of the tobacco smoke effect resulted from the nicotine in the smoke. That finding suggests that e-cigarettes could also represent a significant hazard for women of childbearing age.
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