Medical Information

DETECTING DISORDERS DURING PREGNANCY

Many development problems and genetic disease can now be diagnosed while the fetus is in the uterus.Ultrasound imaging,which generates image using sound frequencies above the normal hearing range,is commonly used to analyze the fetus’ size and condition.In amniocentesis and chorionic villus sampling,a needle is used to obtain fetal cells from fluid or tissue surrounding the embryo;these cells then provide the basis for genetic analysis.

In the newest reproductive technology,a pregnant mother’s blood is used to analyze the genome of her fetus.A pregnant’s mother blood contains DNA from the growing embryo.How does it get there?The mother’s blood reaches the embryo through the placenta.When cells produced by the embryo grow old,die and break open within the placenta,the released DNA enters the mother’s circulation.Although the blood also contains pieces of DNA from the mother,about 10-15% of the DNA circulating in the blood is from the fetus.Both the polymerase chain reaction(PCR) and high throughput sequencing can convert the bits of fetal DNA into useful information.

Unfortunately,almost all detectable disorders remain untreatable in the uterus and many cannot be corrected even after birth.Genetic testing may leave parents faced with difficult decisions about whether to terminate a pregnancy or to raise a child who may have profound defects and a short life expectancy.These are complex issue that demand careful,informed thought and competent genetic counseling.

Parents will be receiving even more genetic information and confronting further questions in the near future.Indeed,in 2012 we learned of the first infant whose entire genome was known before birth.Nevertheless,completing a genome sequence does not ensure complete information.Consider,for example,Klinefelter Syndrome,in which males have an extra X chromosome.This disorder is quite common,affecting 1 in 1000 men,and can cause reduce testosterone,a feminized appearance, and infertility.However,while some men with an extra X chromosome have a debilitating disorder,others have symptoms so mild that they are unaware of the condition.For other disorders,such as diabetes,heart disease,or cancer,a genome sequence may only indicate the degree of risk.How parents will use this and other information in having and raising children is a question with no clear answers.