新的血液检测能在怀孕七周时就能鉴别胎儿的性别

一个简单的血液化验就能在怀孕七周的时候判别胎儿的性别。专家指出这个技术可以帮助家长在有性别相关疾病考量时作出正确决定。但这个技术也有与伦理学冲突的地方，这就是说人们可以选择胎儿的性别。

为此，一些公司拒绝把这一化验卖给中国和印度，因为这两个国家都有重男轻女的现象，如果发现是女婴，就会人工流产。。。

A simple blood test that can determine a baby's sex as early as seven weeks into pregnancy is highly accurate if used correctly, a finding that experts say is likely to lead to more widespread use by parents concerned about gender-linked diseases, those who are merely curious and people considering the more ethically controversial step of selecting the sex of their children.

The appeal of the test, which analyzes fetal DNA found in the mother's blood, is that it can establish sex weeks earlier than other options, like ultrasound, and is noninvasive, unlike amniocentesis and other procedures that carry small risks of miscarriage. The finding came in a study published online Tuesday in The Journal of the American Medical Association.

The tests have been available to consumers in drugstore chains and online for a few years, but their use has been limited, partly because their accuracy was unclear. One company, which guaranteed 99.9% accuracy as early as five weeks into pregnancy, filed for bankruptcy after a lawsuit by women whose tests showed the opposite sex of the baby they ended up having.

European doctors now routinely use the tests to help expectant parents whose offspring are at risk for rare gender-linked disorders determine whether they need invasive and costly genetic testing.

For example, Duchenne muscular dystrophy affects boys, but if the fetus is not the at -risk sex, such tests are unnecessary. But doctors in the US generally have not prescribed the tests because they are unregulated.

That and other aspects of the pregnancy landscape could change as a result of the new study. The study analyzed reams of research on fetal DNA tests - 57 studies involving about 6,500 pregnancies - and found that tests could determine sex with accuracy of 95% at 7 weeks to 99% at 20 weeks.

The study has wide-reaching implications. One potential worry is that women might abort fetuses of an undesired sex. Several companies do not sell tests in China or India, where boys are prized over girls and fetuses found to be female have been aborted.

REF:  Stephanie A. Devaney, PhD; Glenn E. Palomaki, PhD; Joan A. Scott, MS, CGC; Diana W. Bianchi, MD Noninvasive Fetal Sex Determination Using Cell-Free Fetal DNA：A Systematic Review and Meta-analysis. JAMA. 2011;306(6):627-636.