[ti:US Officials: Twin Births Drop to Lowest Level in 10 Years] [by:www.51voa.com] [00:00.00]更多听力请访问51VOA.COM [00:00.04]United States health officials say the number of twin births nationwide has dropped to their lowest level in 10 years. [00:11.48]The U.S. Centers for Disease Control and Prevention, CDC, reported the decrease. [00:20.60]Twin births nationwide began to increase about 40 years ago, CDC records show. [00:29.00]From 1980 until 2014, the total number rose 79 percent. [00:37.12]But from 2014 to 2018, the twin birth rates fell 4 percent. [00:44.52]Last year, there were 32.6 twins for every 1,000 total births, the CDC reported. [00:54.96]While the latest drop was not huge, officials said they consider it a good sign. [01:02.40]Pregnancy with more than one child raises the risks of complications and death for both the mother and the baby. [01:12.72]Dmitry Kissin is a doctor who works with the CDC's Division of Reproductive Health. [01:20.76]He told The Associated Press that many people do not realize there can be serious risks with twin births. [01:30.04]"In the media," he said, "there are often stories about very cute twins and [01:36.03]talking about how great to have two babies at the same time." [01:40.32]Such stories ignore the health risks, Kissin added. [01:47.12]In 2018, about 124,000 babies born in the United States were twins. That represents about one in every 31 births. [02:01.40]Health experts say there is no single explanation for the falling twin birth rates. [02:09.12]However, Joyce Martin, the lead writer of the report, suggested one likely reason. [02:16.72]She noted that the falling rates were only among white women and in women 30 years of age or older. [02:26.28]Women from these groups are the biggest users of in vitro fertility treatments. [02:34.12]In vitro fertilization is when doctors combine male and female cells to create an embryo, [02:42.07]which is later implanted in a woman's uterus. [02:46.84]This technique results in about 15 percent of all births involving more than one baby. [02:54.16]In the past, it was common for fertility experts to implant two [03:00.31]or more embryos to improve the chances of a successful birth. [03:05.97]This greatly increased the woman's chances of having more than one baby. [03:12.96]In recent years, however, the method has changed. [03:16.60]Fertility specialists now grow embryos longer in the lab and carry out more tests for genetic problems. [03:25.84]They then choose the best single embryo to implant. [03:31.72]The CDC's Dmitry Kissin says that today, about two-thirds of in vitro fertility treatments involve just one embryo. [03:43.56]Aaron Styer is an infertility treatment specialist in Chestnut Hill, Massachusetts. [03:51.28]He told The AP the success rate for one embryo [03:55.30]rose from about 20 percent in the 1980s to around 50 percent today. [04:03.60]Styer said that health insurance companies and medical organizations [04:08.70]have increasingly been pushing doctors to implant just a single embryo. [04:15.68]More and more patients are also accepting the method [04:19.32]to improve their chances of a successful pregnancy, he added. [04:25.88]I'm Bryan Lynn. [04:27.65]更多听力请访问51VOA.COM