WHAT is amniocenthesis? It is a earlier procedure procedure that takes out a small sample of the amniotic fluid for testing. This is the fluid that surrounds the fetus in pregnancy. Amniotic fluid is a clear, pale yellow fluid that which protects the fetus from injury and against infection.Amniocentesis is primarily a medical procedure used in the prenatal diagnosis of genetic conditions. It has other uses – for instance, in the assessment of infection and fetal lung maturity.How is it done?The pregnant women will be laid down and her abdomen will be cleaned by an antiseptic agent.Under the guidance of a real-time ultrasound procedure, a long but fine amniocenthesis needle will be inserted through the abdomen to extract a sample of amniotic fluid.The procedure can be carried out with or without local anaesthetic as it may cause similar pain.Some amniotic fluid will be taken out for testing – usually 1cc per week of gestation will be taken out.The test is usually carried out from 15 weeks of pregnancy as an earlier procedure has higher complications, such as limb deformations and a higher incidence of miscarriages.What are the risk for amniocenthesis?There is a small chance that an amniocentesis could cause a miscarriage (less than 1%, or approximately one in 1,000 to one in 43,000). Injury to you or your baby, infection, bleeding at puncture site and preterm labour are other possible problems that can happen but are extremely rare. However, your chances of having complication are higher if you are carrying twins.What tests can be done?One of the most common tests is karyotyping that takes a look at the 23 chromosomes to detect abnormalities such as trisomies – which include Down Syndrome, Edward Syndrome and Patau Syndrome. Sex chromosome abnormalites such as Turner’s Syndrome and triploidies can also be diagnosed.The microarray analysis test is used to find out if your child has a medical condition caused by a missing or extra piece of chromosome material. It is especially important in finding missing segments of a chromosome commonly known as microdeletions.A microarray can be a useful test to try and find the cause of unexplained issues with learning, physical development or behaviour. It may also be used to help find a diagnosis for people with unexplained birth defects or medical problems, such as seizures.Microarray is the first-line investigation for patients with developmental delay, intellectual disability, autism, epilepsy or congenital abnormalities.Whole Exome Sequencing is a comprehensive genetic test that identifies the genetic cause of your child’s signs and symptoms.It identifies up to 85% of all known genetic abnormalities. It is currently the most extensive test that can be done on amniotic fluid for the unborn foetus.What is an exome?The human genome, the term for an individual’s complete set of DNA, is made up of three billion “letters” (called base pairs). These are, in turn, crammed into 23 pairs of thread-like structures called chromosomes, which are inside every cell in the body.A particular sequence of letters (or DNA) forms a gene and it provides instructions for cellular processes in the body. However, not all DNA does this.Researchers have established only 1% to 2% of all genes provide instructions, or code, for proteins, which are the building blocks of cells. This “coding” portion of the genome is called an exome.Though it is possible to sequence or map out a person’s entire genome, it is costly and requires a great deal of computer storage to house such large amounts of data.Because researchers estimate 85% of all disease-causing genetic variants can be found in the exome, whole-exome sequencing is more commonly done.This article is contributed by consultant obstetrician & gynaecologist, maternal fetal medicine Datuk Dr H. Krishna Kumar.