Your Pregnancy Screening Guide
Currently there are many different fetal screening options in NHS and also private markert. This variety of suggestions is very confusing. In this page we have tried to review the current options of fetal testing and reassurance.
Options of First Trimester Screening in London
What is Early Baby Test ?
Early Baby Test (Early Fetal Test) is City Ultrasound signature screening test. This package works as one appointment clinic at 12 weeks where the mother firstly will have Early Baby Scan and in the second place blood sample for NIPT (Harmony Test).
Early Baby Test combines the advantages of:
- Early Anomaly Scan
- Nuchal Translucency (NT) scan
What is screening?
Fetal screening in pregnancy targets fetal abnormalities. In majority of the cases a pregnancy results in delivering a healthy baby, however it is known that about 3% of the babies will be born with some type of anomaly. In general terms screening is a way of identifying apparently healthy people who may have an increased risk of a particular condition (NHS). In the case of pregnancy there are possibilities to perform screening for common chromosomal anomalies (Down’s, Edwards’ or Patau’s syndromes) and structural anomalies (physical abnormalities).
What is the most common fetal anomaly?
As a group it is congenital heart defects (CHD). Heart defects are structural anomalies and they are not detectable by chromosomal screening tests. One of the difficulties in detection of heart defects is their variety. The structure of the heart is complex and there are about 200 different types of CHD, some of them are very rare. Other common defects include kidneys and neural system. Chromosomal conditions accounts to about 15% of all anomalies. In many cases a fetus with chromosomal anomaly will also have CHD as a part of the syndrome.
What is the tool to screen for structural (physical) anomaly in pregnancy?
Ultrasound is a gold standard for screening and diagnosis of baby’s structural anomalies in the womb. It is very capable in detection of abnormal development, however understandably cannot exclude completely all anomalies, because some of them are not visible on scan.
How common is Down’s syndrome?
The short answer is less than 10% of all fetal anomalies.
The incidence of Down’s syndrome (or trisomy 21) is about 1 in 600-800 pregnancies. The occurence increases with the age of mother. Undoubtfully that Down’s syndrome is the commonest fetal syndrome, however there is serious misconception regarding frequency of chromosomal anomalies. Contrary to common believe that Down’s syndrome accounts for majority of abnormal fetuses its real incidence is just below 10% of all fetal anomalies (data of EUROSTAT). For instance, incidence of congenital heart defects is much higher (35% from all anomalies). Down’s syndrome is also not the severest fetal anomaly and some structural brain anomalies and other defects have worse outcome. Other fetal conditions are even lethal and sadly there is no any treatment to prevent fetal or neonatal death.
Can screening test diagnose Down’s syndrome?
No. Any screening test will not tell you whether your baby does or does not have Down’s, Edwards’ or Patau’s syndromes – it will tell you if you have a higher or lower chance of having a baby with one of these conditions.
What is diagnostic test for Down’s syndrome?
There are two invasive diagnostic tests: chorionic villus sampling (CVS, placental biopsy) or amniocentesis. Both performed by fine needle which is passed through the mother’s tummy into the uterus and have risk of miscarriage about 0.5-1%. Those tests are performed for screen positive patients in fetal medicine units of the hospitals.
Can screening test be also diagnostic?
Yes, for structural anomalies screening test can be also diagnostic. It depends on qualification of the operator and type of anomaly. If operator can perform correct diagnosis of specific condition during screening ultrasound test the test become diagnostic. If the fetus has for example spina bifida the correct diagnosis can be established on screening scan. In practice the cases of diagnosed on screening anomalies are referred to fetal medicine units of the hospitals for confirmation and further management. It does not work for chromosomal conditions and there is no way of diagnosis without an invasive test.
NHS screening program.
NHS has one of the best free screening fetal programs in the world. It consists of screening for Down’s syndrome, Patau’s syndrome and Edwards’ syndrome at 11-13 weeks by Combined Screening Test and screening for physical abnormalities (18-21 weeks anomaly scan). In general, the program is very robust and is capable of detection majority serious fetal conditions. On the other hand, the program is still not updated to include rapidly progressing developments in ultrasound and human genetics and there are options for fetal scanning currently not available in NHS.
What is the major weak point of current fetal screening programs?
Although the majority of providers perform reliable screening for chromosomal defects in the 1st trimester, they delay their fetal structural anomalies screening for the 2nd trimester (20 weeks). The only consistently used 1st trimester structural marker for anomalies is Nuchal Translucency (NT), which is very unspecific. In many cases NT gives false positive results, where in absence of anomalies the nuchal fluid spontaneously resolves with favourable outcome, however produce highest levels of anxiety for the future parents and care providers. We are sure that an addition of Early Fetal Scan aiming to screen for fetal structural anomalies will resolve this imbalance.
Screening test for common chromosomal anomalies (Down’s, Edwards’ or Patau’s syndromes) used in NHS. It combines maternal age with nuchal translucency thickness measurements and with levels of two placental proteins. The detection rate for Downs syndrome is 90-95% and false-positive rate is about 5%. Combined test does not check for structural anomalies. In City Ultrasound we decided not to perform combined test because NIPT have better detection rate and lower false-positive rate for Down’s syndrome.
Nuchal translucency scan.
This is ultrasound scan performed at 11-13 weeks of pregnancy performed in order to measure the amount of fluid in the back of baby’s neck (nuchal translucency). Nuchal translucency (NT) thickness measurement is one of the main components of Combined Screening Test. Increased NT is also nonspecific marker for fetal heart defects, other anomalies and wellbeing. It is important to know that majority of the fetuses with structural anomalies have normal NT. For example, the biggest recent study showed that only 21.3% of babies with heart defects had NT more than 3.5 mm (cut-off used in NHS). It means that 4 babies with heart conditions from 5 (~80%) had NT within normal range. Because of this limitation we converted our NT scans to Early Fetal Scans, where we concentrate our attention for fetal anatomy evaluation rather than level of NT fluid.
Majority of providers also include basic check of fetal anomalies like presence of scull, presence of extremities and abdominal wall closure. We recommend you to check with the provider regarding their checklist for the fetal structures at NT scan.
Noninvasive prenatal testing (NIPT) is a method of determining the risk that the baby will be born with certain chromosomal abnormalities. It is relatively new test which was introduced in clinical practice in last few years. NIPT is based on analysis of small fragments of placental DNA that are circulating in a pregnant woman’s blood, so called cell-free DNA (cfDNA). The test is really good for screening for Down’s syndrome and has detection rate 99.8% and low false positive rate, however it is not diagnostic test and positive results must be confirmed by invasive testing, because they can be false-positive.
NIPT can be done very early (from 10 weeks) and many private clinics perform the test along with dating scan. Although we understand that the mother wishes to be reassured regarding fetal abnormalities as soon as possible, she needs to be aware that the NIPT tests can check only chromosomal defects (which represent only 15% of all anomalies). In our clinical practice we have seen parents which were early reassured by NIPT and unfortunately were consequently diagnosed with lethal or severe fetal physical anomaly on follow-up scans.
Nuchal Translucency scan after low risk NIPT results is somewhat confusing, because NT thickness measurements are primary targeted for chromosomal screening (as part of combined test) rather to meticulous evaluation of fetal anatomy. For this purpose, the test is less sensitive than NIPT. Finding increased NT thickness for the fetus with low risk results of NIPT means that the baby may have other serious condition associated with increased NT or the test is false negative. We are completely aware how those situations are worrying parents, which already have pay for the expensive test, which in this case do not help.
NIPT for other conditions (wide-panel NIPTs).
Some companies-producers of NIPT started marketing of wide panels NIPTs, which can include also sex chromosome abnormalities, microdeletions and triploidy. Those tests, although technologically advanced, are still far away from their approval for wide clinical use. The majority of specialists agree that it is preliminary to introduce those tests for every woman’s screening, especially because those anomalies are rare and the tests for them are less accurate.
Wide panel NIPTs cannot detect structural anomalies.
Which NIPT is better?
There are many different commercial companies performing NIPT in UK under different trade names. They all use different genetic technologies, different reporting systems and have different price lists. It is very difficult and confusing for parents and service providers to compare objectively different providers. To avoid confusion of the parents and after detailed review City Ultrasound decided to work with only one provider with which we have good experience of working together. This is Harnony Test by Ariosa Diagnostic which is a healthcare partner of Roche.
Early Baby Scan (Early Fetal Scan).
We are experts in early fetal anomaly screening and early detection of fetal anomalies. During years of research and experience we have developed an advanced top-to-toe comprehensive 1st trimester scan examining fetal structures. We have called this brand-new ultrasound examination Early Baby Scan (Early Fetal Scan) – because it is an earliest scan when it is possible to check the baby. At 10 weeks the baby has finished its embryologic development and become a little human. It is technically possible to perform the Early Baby Scan from 11 weeks, however we prefer to perform it at 12-13 weeks, when the views are better.
Early fetal scan can detect majority of lethal and severe fetal conditions and it specially targeted to spina bifida, early severe brain anomalies, severe heart defects and other serious abnormalities.
Do we check NT on Early Baby Scan?
We check fetal face and profile and perform NT assessment and NT thickness measurements in this scanning plane. We do not use NT measurements for Down’s syndrome assessment (because for this we use NIPT), however refer fetuses with increased measurements (NT more than 3.5 mm) for further assessment in a hospital.
Where else can you perform Early Baby Scan in UK?
To our knowledge we provide a unique service. We are unaware about other ultrasound screening provider performing Early Fetal Scans in UK. There are many our colleagues around the globe performing similar early fetal assessment. We know that some clinics in UK perform reassurance scans (or early anomaly scans) one month later (at around 16 weeks), however we do not know about checklists of structures on those scans.
We think that the situation needs to be change and more professionals and services need to provide Early Fetal Scan service for the pregnant women in UK. To motivate and train professionals we are running multiple London based courses and conferences. We run annual Early Fetal Scan Conference in London, which this year will be totally devoted to Early Fetal Cardiology. This Conference will be the first major scientific event in this field (early screening and management of heart defects).
We are among international group of professionals who believe that in near future the screening for many structural anomalies especially heart and spina bifida. In Western Europe we are involved in 1st trimester training programs in Sweden, Belgium and Netherlands.
Early Baby Test: Early Reassurance.
We have developed the Best First Trimester Screening Package which combines advantages of Early Fetal Scan and NIPT. This package works as one appointment clinic where the mother will have Early Baby Scan and after blood sample for NIPT. The best time for the scan/NIPT is 12-13 weeks. This advanced approach will resolve current imbalance between early (1st trimester) screening for Down’s syndrome and late (2nd trimester) anomaly scan. Understandably some anomalies will be not visible at this early stage or will develop later and we strongly recommend to perform good quality anomaly scan after 20 weeks to confirm normal development of the baby.
The approach to perform Early Baby Scan just before NIPT can be also money-saving and if the baby unfortunately will have any structural anomalies, or significantly increased NT on the scan the NIPT will be inappropriate test. We will refer the mother to the hospital for further assessment and an invasive test, if needs. Understandably fetuses with lethal anomalies will not benefit from NIPT.