IVF smokescreen

日期:2019-03-07 07:15:02 作者:谯掼暨 阅读:

By Alison Motluk SMOKING appears to improve a woman’s chances of producing healthy-looking embryos suitable for IVF, according to a fertility researcher in Canada. But the effect is deceptive—in fact, smoking disguises defects and increases the chances of a miscarriage later on. Maria Zenzes of the University of Toronto wanted to see how a mother’s smoking affected her fertilisation rate and the quality of her embryos. She had shown earlier that damage from carcinogens in cigarette smoke can be passed from a smoking father to his embryo through damaged sperm. Zenzes looked at 1682 embryos from 271 women who were undergoing IVF. At the two-cell and eight-cell stage, she categorised the embryos as “good” or “poor” quality. The good-quality embryos showed few of the hallmarks of programmed cell death, such as fragmentation of the nucleus. In IVF, technicians decide which embryos to transfer by looking for signs of cell death and choosing those that look the most healthy. Zenzes assessed how much the women smoked by measuring levels of cotinine, a breakdown product of nicotine, in the fluid surrounding their eggs. After controlling for maternal age, which can also affect fertilisation rate and embryo quality, she found to her surprise that smoking seemed to be a help rather than a hindrance. The more a woman smoked, the higher her fertility rate and the greater the proportion of sound embryos that she produced. “The number of embryos of good-looking quality is significantly higher in smokers,” she says. “That’s somehow counterintuitive.” Women who smoke are known to suffer more miscarriages, according to Edward Reed, co-author of the study. Cigarette smoke contains a carcinogen called benzopyrene, which is known to inhibit programmed cell death in tumours of the lung. So smoking may keep alive defective cells that would normally be weeded out. “Even if the embryos look better, they may have genetic abnormalities that are hidden,” Zenzes says. This may make it difficult to identify which embryos are the best bet for transfer, she says, and lead to more miscarriages down the line. More on these topics: