First Trimester Screening including NT scan.
This screening involves an ultrasound assessment of the fetus including the nuchal translucency, and the new markers such as nasal bone, tricuspid regurgitation and ductus venosus PI.
The maternal blood is also checked for PAPPA and free beta- HCG and an integrated risk assessment is given.
The First Trimester Screening (FTS) test has important implications for you and your family and explained here is how it is performed and what the results mean. Before undergoing this test it is very important that you have discussed this testing procedure.
What is the difference between a screening test and diagnostic test?
Tests which tell if your baby has a particular disease or condition with some certainty are called diagnostic tests. On the other hand, screening tests only show if your baby’s chance is high or low for a specific disease or condition. If the chance is increased, you can then choose to have a diagnostic testing.
What conditions are covered in first trimester screening?
The vast majority of babies are normal. However all women, whatever their age, have a small risk of delivering a baby with a physical or a mental abnormality. In some cases this may be due to chromosomal problems such as Down syndrome, Trisomy 13 or Trisomy 18. These conditions are mainly looked for in the first trimester screening.
Chromosomes contain the genetic information we require to grow and develop normally. Each cell contains 23 pairs of chromosomes. Down syndrome usually occurs by having 3 copies of chromosome 21.
It occurs in about 1 in every 700 pregnancies and is an important cause of congenital intellectual disability. It causes mental retardation and various medical problems involving the heart, digestive tract, and/or other organ systems.
Trisomy 18 (having an extra chromosome 18) and trisomy 13 (having an extra chromosome 13) are more severe disorders which cause profound mental retardation and severe birth defects in many organ systems. Few babies with trisomies 13 or 18 survive more than a few months.
What causes this replication is still unknown, no racial, geographical, social, economic or environmental factors have been identified. Anyone can have a baby with these chromosome abnormalities, however, the chance increases with the mother’s age, but a child with Down Syndrome can be born to a mother of any age.
Who should be screened?
Leading medical professional organizations recommend first trimester Down syndrome screening for all pregnant women, regardless of age.
How does first trimester screening assess your baby’s risk?
First trimester screening is not a diagnostic test, which means it cannot tell you whether your baby has Down syndrome, trisomy 13, or trisomy 18. Instead, the screening provides a probability that your baby might have Down syndrome, trisomy 13, or trisomy 18.
This probability or chance is based on the following criteria:
• Your age
• Nuchal Translucency (amount of fluid behind the neck of the fetus on ultrasound)
• Presence or absence of any physical abnormalities on ultrasound
• Level of two proteins (Fß-hCG and PAPP-A) in your blood.
The screening results can either alert you and your doctor that your baby is at an increased risk for one of these chromosome disorders or be reassuring that your baby is at a lower risk for these conditions.
Women at high risk are offered further tests. It is important to remember that most women will have normal babies, even if they are grouped as high risk. |
How and when is the test performed?
It involves two tests, a blood test and an ultrasound.
Blood Test – We recommend women have the blood test at week 10 of pregnancy. However, the blood test can be performed up until 13 weeks and 6 days of pregnancy. It analyzes two chemicals called free beta-human chorionic gonadotropin (hCG) and pregnancy associated plasma protein-A (PAPP-A), which are found in the blood of all pregnant women.
Ultrasound – The ultrasound can be performed from 11 weeks through to 13 weeks and 6 days of pregnancy. It is a highly specialized ultrasound. It takes about 30-40 minutes or even longer.
The scan will confirm how far along your pregnancy is. In addition, a measurement of the fluid underneath the skin along the back of the baby’s neck, called the nuchal translucency (NT), will be taken. The scan will also determine if your baby’s nasal bone is present or absent.
Combining your age-related risk with the NT measurement, nasal bone data, and blood work, provides you with one risk figure for Down syndrome and one risk figure for trisomy 13 or trisomy 18.
This special scan also provides other very useful information:
• Accurate dating of the pregnancy
• Fetal heart rate
• Number of fetuses present and, if twins, whether they are identical or not
• Detects obvious fetal abnormalities |
What are the risks and side effects to the mother or baby?
Except for the discomfort of drawing blood, there are no known risks or side effects associated with the First trimester screen.
How accurate is First Trimester Screening?
Because this is a screening test, a positive result (showing an increased risk) does not mean that your baby has a problem, only that further diagnostic tests are options for you to consider. Also, a negative or normal result (one that shows a decreased risk) does not mean that the baby will not have a chromosome abnormality.The first trimester screen’s detection rate is approximately 96% for pregnancies in which the baby has Down syndrome, and is somewhat higher for pregnancies with trisomy 13 or trisomy 18. There is a 5% false positive rate for the test. Parents should be aware of the possibility of receiving abnormal results and then finding, after further testing, that the baby is normal.
Finally, this screen is not designed to provide information about the possibility of other chromosome conditions, nor about many other genetic syndromes, genetic disorders, birth defects, or causes of mental retardation.
UNDERSTANDING YOUR RESULTS
What does a “screen negative” result mean?
A screen negative result means that the risks for Down syndrome, trisomy 13, and trisomy 18 are low enough that diagnostic testing (CVS or amniocentesis) is not indicated. The majority of pregnant women have a “screen negative” result. Although a “screen negative” result greatly reduces the risk for the screened chromosome abnormalities, it does not completely rule out the possibility that the fetus is affected.
It is important to remember that a screening test does not guarantee a normal baby.
If your First Trimester Screen is “screen negative”, your obstetrician will provide you with routine obstetrical care.
What does a “screen positive” result mean?
A screen positive result means that there is an increased risk for Down syndrome, trisomy 13, or trisomy 18 in the pregnancy. A screen positive result does not mean that the fetus is affected with the condition, only that a pregnancy has an increased risk for the condition. Most women with “screen positive” results have healthy babies.
When the result is “screen positive”, the following options are available:
- Diagnostic testing by chorionic villus sampling (CVS) performed between 10-13 weeks
- Diagnostic testing by amniocentesis performed after 15 weeks
- Second trimester maternal serum screening drawn after 15 weeks to obtain a combined first and second trimester screening result
- Detailed anatomy ultrasound performed at approximately 18-20 weeks
What are the diagnostic tests available?
Diagnostic tests will usually involve amniocentesis or chorionic villus sampling, which take a small amount of fluid or tissue from around the baby for chromosomal analysis.
Both tests have a small risk of miscarriage.
CVS and amniocentesis are diagnostic tests that can tell you with greater than 99% accuracy whether or not a baby has a chromosome abnormality.
Final results from the chromosomal analysis may take 2-3 weeks. Sometimes an interim result may be available in a few days. We will discuss the results with you and assist you in deciding about diagnostic tests, such as CVS or amniocentesis.
Antenatal Schedule
Name: D.O.B:
EDD:
Dating Scan (7-10 weeks): Yes/No
NT Scan (11-13+ 6): Yes/No
Double Test (11-13+6): Yes/No
Quadruple Test (16-20+6): Yes/No
Anomaly Scan (TIFFA) + Fetal Echo (18-19): Yes/No
Growth Scan:
28 weeks: Yes/No
32-34 weeks: Yes/No
Pregnancy Profile Blood: (to complete < 20 weeks)
Blood Group:
CBP:
HCV, Hep B, HIV, VDRL:
TT injection x 2 doses: (4 weeks apart) Yes/No
GTT: 22 weeks Yes/No
CBP:
|
Date |
10-18 weeks |
24 week |
30 weeks |
36 weeks |
Hb |
|
|
|
|
Antenatal Check ups:
Upto 28 weeks 4 weekly
From 28 weeks: Every 2 weeks
From 34 weeks: Every Week
Medication:
Folic Acid: Yes/No
Iron: Yes/No
Calcium: Yes/No
Progesterone: Yes/No
Aspirin: Yes/No
Vit D: Yes/No
Other Medication: Yes/No
Aneuploidy screening -1
- Appointments offered through dedicated Tel contact and basic information provided regarding screening
- On arrival detailed history obtained by the trained named nurse and information all entered onto Obstetric software database
- I study the patient details and review the patient prior to US and offer serum screening and US screening and combination of both
Aneuploidy screening – 2
- A detailed scan carried out following consent
- Scan findings entered on software
- Aneuploidy risk algorithm applied to obtain the risk for the maternal age and gestation
- Results discussed with the patient and counselling done and complete antenatal plan would be provided to the patient in the given report
