血液中の男性性染色体の小片を見つけ出す検査である。これが見つかれば胎児は男だとわかる。いくつかのヨーロッパの病院ではすでにcell-free fetal DNAと呼ばれて実施している。
Mother's blood test reveals baby's sex
By Frederik Joelving
NEW YORK | Tue Aug 9, 2011 5:37pm EDT
(Reuters Health) - Blood drawn from expectant mothers could offer parents an earlier sneak peek at their baby's sex than methods currently used in the U.S., researchers said Tuesday.
The test may be particularly valuable for families that harbor sex-linked genetic disorders like hemophilia, they add.
Because such disorders mostly strike boys, knowing that the baby is a girl could spare the mother diagnostic procedures, such as amniocentesis, that carry a small risk of miscarriage.
"It could reduce the number of invasive procedures that are being performed for specific genetic conditions," said Dr. Diana Bianchi of Tufts University School of Medicine, who worked on the new study.
But other researchers voiced concerns, saying it could be misused to terminate a pregnancy if the baby isn't of the desired sex.
"What you have to consider is the ethics of this," said Dr. Mary Rosser, an obstetrician and gynecologist at the Montefiore Medical Center in New York.
"If parents are using it to determine gender and then terminate the pregnancy based on that, that could be a problem," she told Reuters Health. "Remember, gender is not a disease."
The test looks for small pieces of the male sex chromosome in the mother's blood, which would mean she is carrying a baby boy. Some European hospitals already rely on the method, called cell-free fetal DNA, although it's not available from doctors in the U.S.
"What they are finding in England is that many women are not going on to have the invasive tests," Bianchi told Reuters Health.
In those procedures, doctors either extract a small amount of the fluid that surrounds the fetus (amniocentesis) or they take a sample of the placenta (chorionic villus sampling). Between one in 100 and one in 600 mothers miscarry as a result, according to Bianchi.
In a fresh look at the medical evidence for the blood test, she and her colleagues analyzed 57 earlier studies that included more than 6,500 pregnancies.
They found parents could trust the test 98.8 percent of the time when it said they'd have a boy, and 94.8 percent of the time when it indicated a girl.
That leaves some room for error, which could be important if parents are making medical decisions based on the results -- such as whether or not to get an invasive procedure to look for genetic disorders.
However, the current non-invasive alternative -- an ultrasound done at the end of the first trimester -- isn't always good at spotting a baby's sex, Bianchi's team reported in the Journal of the American Medical Association.
And the blood test is reliable as early as seven weeks into the pregnancy, whereas ultrasound is not.
Bianchi said one study had estimated the blood test costs about 255 pounds in the UK (about $413), all included. While it's available over the Internet, she said her team had only looked at hospital-based test performance.
"I don't know why it is not being incorporated in the US," she said.
Rosser, however, chalked that up to the ethical issues it raises.
"It is a great test that can be part of our armamentarium of noninvasive testing that we use," she said. "But it should only be used by families that are at risk for sex-linked diseases."
Bianchi said she owns stock in Verinata Health, a company that is developing cell-free fetal DNA tests for Down syndrome, although that company had no role in the new study.
The American College of Medical Genetics did not respond to requests for comment on the DNA tests.
SOURCE: bit.ly/4HWZ7 Journal of the American Medical Association, August 10, 2011.
(This story has been corrected in paragraph 3 to show said disorders mostly strike boys, not only strike boys)
Noninvasive Fetal Sex Determination Using Cell-Free Fetal DNA
A Systematic Review and Meta-analysis
Stephanie A. Devaney, PhD;
Glenn E. Palomaki, PhD;
Joan A. Scott, MS, CGC;
Diana W. Bianchi, MD
[+] Author Affiliations
Author Affiliations: Genetics and Public Policy Center, Johns Hopkins University, Washington, DC (Dr Devaney and Ms Scott); Department of Health and Human Services, National Institutes of Health, Bethesda, Maryland (Dr Devaney); Women & Infants Hospital, Alpert Medical School of Brown University, Providence, Rhode Island (Dr Palomaki); National Coalition for Health Professional Education in Genetics, Lutherville, Maryland (Ms Scott); and Mother Infant Research Institute at Tufts Medical Center and Division of Genetics, Floating Hospital for Children, Boston, Massachusetts (Dr Bianchi).
Context Noninvasive prenatal determination of fetal sex using cell-free fetal DNA provides an alternative to invasive techniques for some heritable disorders. In some countries this testing has transitioned to clinical care, despite the absence of a formal assessment of performance.
Objective To document overall test performance of noninvasive fetal sex determination using cell-free fetal DNA and to identify variables that affect performance.
Data Sources Systematic review and meta-analysis with search of PubMed (January 1, 1997-April 17, 2011) to identify English-language human studies reporting primary data. References from review articles were also searched.
Study Selection and Data Extraction Abstracts were read independently to identify studies reporting primary data suitable for analysis. Covariates included publication year, sample type, DNA amplification methodology, Y chromosome sequence, and gestational age. Data were independently extracted by 2 reviewers.
Results From 57 selected studies, 80 data sets (representing 3524 male-bearing pregnancies and 3017 female-bearing pregnancies) were analyzed. Overall performance of the test to detect Y chromosome sequences had the following characteristics: sensitivity, 95.4% (95% confidence interval [CI], 94.7%-96.1%) and specificity, 98.6% (95% CI, 98.1%-99.0%); diagnostic odds ratio (OR), 885; positive predictive value, 98.8%; negative predictive value, 94.8%; area under curve (AUC), 0.993 (95% CI, 0.989-0.995), with significant interstudy heterogeneity. DNA methodology and gestational age had the largest effects on test performance. Methodology test characteristics were AUC, 0.988 (95% CI, 0.979-0.993) for polymerase chain reaction (PCR) and AUC, 0.996 (95% CI, 0.993-0.998) for real-time quantitative PCR (RTQ-PCR) (P = .02). Gestational age test characteristics were AUC, 0.989 (95% CI, 0.965-0.998) (<7 weeks); AUC, 0.994 (95% CI, 0.987-0.997) (7-12 weeks); AUC, 0.992 (95% CI, 0.983-0.996) (13-20 weeks); and AUC, 0.998 (95% CI, 0.990-0.999) (>20 weeks) (P = .02 for comparison of diagnostic ORs across age ranges). RTQ-PCR (sensitivity, 96.0%; specificity, 99.0%) outperformed conventional PCR (sensitivity, 94.0%; specificity, 97.3%). Testing after 20 weeks (sensitivity, 99.0%; specificity, 99.6%) outperformed testing prior to 7 weeks (sensitivity, 74.5%; specificity, 99.1%), testing at 7 through 12 weeks (sensitivity, 94.8%; specificity, 98.9%), and 13 through 20 weeks (sensitivity, 95.5%; specificity, 99.1%).
Conclusions Despite interstudy variability, performance was high using maternal blood. Sensitivity and specificity for detection of Y chromosome sequences was greatest using RTQ-PCR after 20 weeks' gestation. Tests using urine and tests performed before 7 weeks' gestation were unreliable.
CHROMOSOMES, HUMAN, Y,
GENETIC DISEASES, Y-LINKED,
REVERSE TRANSCRIPTASE POLYMERASE CHAIN REACTION,
SEX DETERMINATION (GENETICS).
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