These are invasive diagnostic tests designed to confirm chromosomal disorder, such as Down syndrome and genetic diseases. Chromosomes carry genes that pass certain characteristics from parents to their children. When there are too many or too few chromosomes, or there is a defect in a chromosome, birth defects usually occur. These tests are usually offered to women who have an increased chance of having a baby with a disorder eg women over 35 years old, women who have had a previous Down Syndrome child or other chromosomal disorders, or women who know that they or their baby’s father have an unusual chromosomal arrangement. It is not usually offered on a routine basis.
- Amniocentesis is a procedure in which a small amount of the amniotic fluid surrounding the baby in the womb is removed by passing a fine needle through the mother’s abdomen.
- The safest time to have amniocentesis is after 16th week but before 20th week of pregnancy.
- About 0.3-0.2% of women who have amniocentesis from 15th week of pregnancy under ultrasound guidance miscarry as a result of the procedure.
- It takes a few days to about 3-4 weeks for the results to be available. If a disorder is diagnosed, you will be given information and ample opportunities to discuss this with us.
- Chorionic villus sampling (CVS) is a prenatal test that detects chromosomal abnormalities (eg. Down syndrome) and a host of other genetic disorders (eg. cystic fibrosis, sickle cell disease and thalassemia). Cells are taken from tiny finger-like projections on the placenta called chorionic villi and are sent to a lab for genetic analysis.
- The main advantage of CVS over amniocentesis is that it can be performed earlier — generally between 11 and 12 weeks of pregnancy so you can find out about your baby’s condition sooner.
- The miscarriage rate associated with CVS is between 0.5 to 1% and the risk of fetal limb abnormalities is minimised when performed after 11 weeks.
- Unlike amniocentesis, CVS cannot test for neural tube defects as no amniotic fluid is removed.
- Results are usually available in a few days to about 7 to 10 days.
- The vast majority of babies are normal. However all women, regardless of age, have a small chance of delivering a baby with physical problems. The routine detailed ultrasound scan is used to diagnose and exclude these abnormalities in your baby by examining your baby’s anatomy, assessing normal growth, checking the placental position and cervical status. Performed between 20 to 24 weeks, this pregnancy scan detects up to 90% of significant abnormalities.
- A 3D scan provides a life-like image of your baby and a 4D scan is a real-time moving image of the baby. These scans should take about 30 minutes although it may take longer depending on your baby’s position and movement. These scans are not meant to replace the routine 2nd trimester screening scans.
- This form of ultrasound has changed the way in which we can all view your developing baby. Our patients find both 3D and 4D scanning very reassuring that their baby is developing normally.
These tests to monitor fetal health include fetal movement counts, ultrasound and cardiotocography (CTG).
- Fetal movement counting is a test that you can do at home to track your baby’s movements to help check on your baby’s health. You will need to alert us if there is a change from the normal pattern or number of movements.
- The growth scan, which is done from 24 to 41 weeks, assesses the baby’s growth and evaluates the placental location, amniotic fluid volume as well as fetal movements. The use of colour Doppler ultrasound is used to assess the blood flow in the umbilical cord and other blood vessels in the baby. The results from this test can help determine if the fetus is under stress and if the blood is circulating properly.
- The CTG measures your baby’s heart rate and wellbeing.