Prenatal Screening for Down’s ,Preeclampsia,FGR& Preterm labor
What is Down’s Syndrome?
Down Syndrome (DS) is generally referred as a chromosomal disorder in which the individual who is affected has one extra chromosome in addition to what is the normally allocated number of chromosomes. Each individual has total number of 46 chromosomes, each arranged in a pair of 23. People having Down Syndrome, the 21th pair of chromosome has three copies instead of two, so the total pair of chromosomes is 47 instead of normal 46.The sperm of man has 23 chromosomes pair and like wisely, of woman’s egg. When conception occurs and the sperm fertilises the egg, a new human being with a full supplement of chromosomes is formed. Many a times due to flaws of fertilization what results is known as Chromosomal Abnormalities. Down’s syndrome is one of the family of these. At conception, ideally one 21 chromosome from the father and one from the mother comes together, but instead a third chromosome crawls in and is then replicated in each cell of the baby’s body. Down’s Syndrome, is also known as Trisomy 21, that is most familiar chromosomal abnormality, that occurs approximately once in every 600 births.
Why should we test for Down’s syndrome?
Down’s syndrome – common chromosomal abnormality, can have major impacts on your family socially, financially and emotionally. It is the most usual cause of delay in children for global development, that is not inherited.
Down’s syndrome occurs in every 1 in 800 pregnancies in India. Any woman can have a baby with Down’s syndrome. The possibilities differ with the age of mother. As the maternal age increases, the chances for Down’s syndrome also increase. At the age of 21, the chances are approximately 1:1200, which is increased to 1:250 at the age of 35 and 1:80 at 40.
Approximately 70% of babies affected with Down syndrome are born to young mothers and thus screening must be offered to all women.
Most of the women risks giving a birth affected with Down syndrome. To detect the threat in this pregnancy of the baby being born with Down’s syndrome, a screening test is offered to all women during early pregnancy.
It is necessary to know that screening test does not give a perfect answer as to whether or not the baby does have Down syndrome. If your screening test shows the high risk about your baby’s Down syndrome, you are offered a diagnostic test.
NT scan and Combined screening
- This type of screening includes an ultrasound assessment of the fetus that involves the nuchal translucency, and the new markers such as nasal bone, tricuspid regurgitation and ductus venosus PI.
- The maternal blood is also checked for PAPP-A, free beta- HCG and an integrated risk assessment is given.
- The First Trimester Screening (FTS) test has necessary intimation for you and your family. Before starting this test it is very essential to discuss this testing procedure.
Cell free fetal DNA test/NIPT –Non Invasive Test
The Quadruple marker test or simply the Quad test is a prenatal test that measures levels of four hormones in a pregnant woman’s blood:
- Alpha-fetoprotein (AFP), a protein made by the developing baby
- Human chorionic gonadotropin (HCG), a hormone made by the placenta
- Estriol, a hormone made by the placenta and the baby’s liver
- Inhibin A, another hormone made by the placenta
Generally, the Quad screening is performed within 15th and 20th week of pregnancy (second trimester).
Solutions for the screening test address your risk of carrying a baby having certain chromosomal conditions, like Down’s syndrome. The alpha-fetoprotein part of the test can help detect neural tube defects, such as spina bifida.
If your risk level is low, the quad screening indicates healthy pregnancy. But if the risk level is moderate or high, you might choose to follow the quad screen with another more definitive test.
Ultrasound for second trimester risk assesment/Genetic sonogram
Genetic Sonogram or the risk reassessment scan is usually performed when the risk of Down’s syndrome has increased on an earlier biochemical screening test.
In this technique, ultrasound is done for specific ultrasound features or soft markers suggestive of T21 like nuchal fold, nasal bone, mild ventriculomegaly, aberrant right subclavian artery.
Specific features are examined that increases or decreases the risk of Down’s syndrome.
At the end a new possibility for Down’s syndrome is given. The genetic sonogram is only 56% effective at marking Down syndrome at a false positive ratio of 3%.
How and when is the test performed?
It has two tests – a blood test and an ultrasound
We suggest women to have blood test at week 10 of pregnancy. Nevertheless, the blood test is performed till 13 weeks and 6 days of pregnancy. It examines three chemicals called free beta-human chorionic gonadotropin (hCG) , pregnancy associated plasma protein-A (PAPP-A), and placental growth factor (PLGF) found in the blood of all pregnant women.
We advise to get an ultrasound done at 12th week of pregnancy. Nevertheless, the ultrasound can be done from 11 weeks to 13 weeks and 6 days of pregnancy. It is highly functional ultrasound and takes about 30-40 minutes.
The sonogram performed will indicate how far along your pregnancy is. More than that, a measurement of the fluid beneath the skin along the back of the baby’s neck, known as nuchal translucency (NT), will be taken. It also determines if your baby’s nasal bone is present or absent. It also checks the blood flow across the valve of the right heart chamber and gaze for the regurgitation (tricuspid regurgitation) and blood across the ductus venosus, the physiological valve regulating blood to the heart.
Joining your age related risk with the NT measurement, nasal bone data, and blood flow gets you with one risk figure for Down syndrome and one risk figure for trisomy 13 or trisomy 18.
More than this, the scan provides other information like:
- Accurate dating of the pregnancy
- Fetal heart rate
- Number of fetuses present and, for twins, if they are identical or not
- Detects obvious fetal abnormalities
Pre-eclampsia arises in around 1 in 50 pregnancies. It is pregnancy induced high blood pressure and is one of the most usual life alarming situations occurring in pregnancy.
Regrettably, high blood pressure can be threatening to both mother and baby. The only treatment is delivery at present and the schedule of this has to be balanced against the state of the pregnancy and therefore the maturity of the baby.
Screening at the time of first trimester can spot women at high-risk for pre-eclampsia. This could likely improve the pregnancy outcome as the better maternal and fetal monitoring would follow the earlier detection of the clinical signs of the disease and wherever the necessary medication can be given.
Moreover, to your 11-13 week of scan, you can choose to have a screening test for this likely serious situation. There may be an extensive proof that early pre-eclampsia is situated with an increased risk to mother and baby’s health.
What do we look for in the Pre-eclampsia screening?
The Pre-eclampsia screening process is quite simple and includes an ultrasound scan to calculate the placental blood flow at 11-13 weeks gestation with integration in maternal history, known as arterial blood pressure, serum PAPP-A maternal blood marker and placental growth factor (PLGF).
Pre-eclampsia Screen – Test accuracy:
It is measured that the combination of method of screening can estimate 90% of early pre-eclampsia cases involving delivery before 34 weeks.
Pre-eclampsia Screen Results: What if screen is positive?
If your screen is positive for pre-eclampsia, it is necessary to remember that the possibility that you will have the condition is still low, but it is suggested that you are most closely tracked in your pregnancy. We inform the healthcare professional taking care after you that the mid trimester scan is done nearly to 20 weeks as possible to check not only baby’s structural development but, most importantly, baby’s growth. We then see you back at our screening clinic at 23 – 24 week repeatedly to check the growth of baby, uterine artery Doppler, your blood pressure and urine. At this stage, if everything is fine, your doctor will continue to monitor you blood pressure and urine throughout the pregnancy on routine basis.
Pre-term labor screening
Premature also known as preterm labour is usually when you have labour pain before 37 weeks of pregnancy that opens and shortens your cervix. This leads to the baby born too early.
Approximately, 1 in 10 babies are born premature.
How can you predict the risk of preterm baby?
By transvaginal ultrasound, cervical screening is performed for all women at 18-24 weeks. The cervix length is calculated in a mid saggital plane. The normal length is usually > 25 mm. We routinely perform a transvaginal ultrasound for all pregnant ladies at different points during pregnancy to evaluate threat of preterm labour (11-13 weeks, 18-24 weeks).