FIRST TRIMESTER SCAN:
INFORMATION ABOUT THE FETAL EXAMINATION AT 12-13 WEEKS
A few basic facts:
- Almost every newborn baby is born healthy and without any malformations or genetic disorders!
- Every woman carries a small risk of giving birth to a physically and/or mentally impaired baby.
- In some cases the impairment is due to a genetic disorder (usually Trisomy 21 = Down syndrome).
- The risk of the most common genetic disorders can be estimated at the ultrasound scan at 12-13 weeks. This evaluation takes into consideration the mother’s age, the ultrasound findings (nuchal translucency, nasal bone formation etc.) and some blood test results. At this scan we can also exclude a range of serious malformations.
- The result of the examination at 12-13 weeks provides, among other things, a risk estimate for Down syndrome. This is currently the most reliable non-invasive procedure performed during pregnancy.
- This examination is performed at our clinic only by specially trained physicians (certified by FMF London, DEGUM II) using high-end equipment (GE Voluson E8).
- A range of physical defects, but certainly not all, can be detected at this early examination. For all our patients we recommend an additional, more precise ultrasound scan after 20 weeks’ gestation.
- Standard health insurance and even some forms of private health insurance do not cover this examination, you will be paying for it directly.
- To definitely exclude or confirm a genetic disorder (chromosomal anomaly) in the baby, an invasive procedure must be performed (chorion villus biopsy or amniocentesis). However, these procedures bear a miscarriage risk of 0.5-1%.
RISK ASSESSMENT FOR DOWN SYNDROME DEPENDING ON THE MOTHER’S AGE
The chart shows the risk for Down syndrome increasing in direct relation to the mother’s age. The likelihood of a genetic disorder is actually higher at the beginning of pregnancy than at the due date, because many affected children die during pregnancy without any external intervention or influence.
Likelihood of a live birth with Down syndrome and the likelihood of Down syndrome at 12 weeks of pregnancy in relation to the mother’s age:
Age (years) |
Risk of Down Syndrome |
|
|
At term (live birth) |
At 12 weeks (completed) |
20 |
1 in 1526 (0.6 in 1000) |
1 in 1068 (0.94 in 1000) |
25 |
1 in 1351 (0.7 in 1000) |
1 in 946 (1.05 in 1000) |
30 |
1 in 894 (1.1 in 1000) |
1 in 626 (1.59 in 1000) |
32 |
1 in 658 (1.5 in 1000) |
1 in 461 (2.17 in 1000) |
34 |
1 in 445 (2.2 in 1000) |
1 in 312 (3.20 in 1000) |
36 |
1 in 280 (3.6 in 1000) |
1 in 196 (5.10 in 1000) |
38 |
1 in 167 (6.0 in 1000) |
1 in 117 (8.55 in 1000) |
40 |
1 in 96 (10.4 in 1000) |
1 in 68 (14.7 in 1000) |
42 |
1 in 55 (18.2 in 1000) |
1 in 38 (26.3 in 1000) |
44 |
1 in 30 (33.3 in 1000) |
1 in 21 (47.6 in 1000) |
HIGH RESOLUTION ULTRASOUND SCAN AT 12-13 WEEKS
This investigation can only be performed during the time from the completed 11th (11+0) week of pregnancy until shortly before the 13th week is completed (13+6). The ideal time for the scan is between the completed 12th and 13th week of pregnancy (12+0 until 13+0). The blood test can be done in advance, after 10 completed weeks. This way, the informative value of the blood test is enhanced and all results can be discussed on the day of the ultrasound scan. The scan is performed with the transducer on your lower abdomen, very occasionally we use a transducer inside the vagina (please make sure your bladder is empty!). At this scan we check the baby’s heartbeat and confirm exactly how far along you are.
Following this, the entire fetus is visualised on ultrasound in order to find or exclude developmental problems as far as possible at this early stage of pregnancy. We determine the size of the baby’s nuchal translucency and see whether the nasal bone and certain blood flows (e.g. within the baby’s heart) can be visualised by ultrasound. As a compound result it is possible to calculate the risk for Down syndrome and other trisomies (Trisomy 18 – Edwards Syndrome,Trisomy 13 – Patau Syndrome) taking into account your age, the levels of certain blood parameters and the results of the ultrasound scan.
RISK CALCULATION FOR TRISOMIES
Every baby between 11 and 13 weeks of pregnancy has a nuchal translucency, which is a dark area (fluid) at the back of the developing neck. We know this because of a study of the Fetal Medicine Foundation in London we have participated in since mid-1997, which included more than 100’000 pregnant women. The more fluid is detected in the back of the baby’s neck – the wider the nuchal translucency –, the higher the likelihood of a genetic disorder, especially Down syndrome. We make use of the Fetal Medicine Foundation computer programme, which was made available to study participants, to assess your personal risk taking into account the fetal nuchal translucency, your age and blood test results.
YOUR DECISION
Depending on the result of the risk assessment, you can continue without further investigations or wish for a definitive answer to the question of whether or not your child is affected by a genetic disorder. We are trained to perform procedures like chorion villus biopsy or amniocentesis, which allow your baby’s chromosomes to be obtained and examined. The advantage of these invasive procedures is that you receive a definitive answer. The disadvantage is that they carry a miscarriage risk of 0.5-1%!
FUTHER MEANS OF INVESTIGATION
The combination of ultrasound scan and maternal blood tests at 11-13 weeks, taking maternal age into account, currently provides the most accurate risk assessment for genetic disorders during the entire course of pregnancy.
The ultrasound scan at 12-13 weeks can exclude or detect a range of serious malformations. However, many problems can only be identified later in pregnancy. We therefore recommend an additonal detailed
ultrasound scan at 20-22 weeks.
If you are finding it difficult to make a decision or need additional information, we can offer you expert genetic counseling at our clinic before further investigations are performed.
SUMMARY OF DIAGNOSTIC MEANS FOR RISK ASSESSMENT OF A GENETIC DISORDER IN YOUR BABY:
- First trimester screening (Nuchal translucency)/maternal serum screening at 12-13 weeks
- Detailed ultrasound (“anomaly”) scan at 20-23 completed weeks
The early scan at 12-13 weeks is the most reliable for risk assessment of a trisomy (Down syndrome)!
Please bear in mind that these investigations provide
a risk estimation for genetic disorders.
If you require
a definite answer to the question of whether a genetic disorder is present or not, an invasive investigation can be performed:
Both procedures carry a miscarriage risk of 0.3 to 1%!
Information about pregnancy outcome is a very important part of our work. You will receive a questionnaire after the examination. We would very much appreciate it if you could fill out the questionnaire after your delivery and send it back to us.