This is a scan usually carried out trans-vaginally at 6 weeks to 10 weeks of pregnancy. The scan can determine the number of fetuses present and whether the pregnancy is progressing normally inside the uterus. It is useful for women who are experiencing pain or bleeding in the pregnancy and those who have had previous miscarriages or ectopic pregnancies. The figure shows a normal pregnancy at 7 weeks of gestation.
1ST TRIMESTER SCANS
1ST TRIMESTER SCANS WILL BE DONE TO:
- Confirm a normal intrauterine pregnancy
- Exclude extra-uterine pregnancy or miscarriage
- Determine the fetal age by measuring the length of the embryo (this will establish the dating of the pregnancy)
- Determine the baby’s heart rate
- Look for multiple pregnancies (twins, triplets, etc.)
- Identify problems of the placenta, uterus, cervix, and ovaries
HOW ACCURATE IS PREGNANCY DATING?
A measurement of the length of the embryo at 7-11 weeks’ gestation is accurate to within about 3 days. Beyond this time the accuracy reduces due to flexion (bending) of the fetus and individual’s growth variance.
This scan is carried out from 11 weeks to 13 weeks and 6 days. The scan is usually performed trans-abdominally as well as trans vaginally . The ultrasound allows a measurement to be taken of the thickness of fluid in an area behind the fetal neck. This area, known as the nuchal translucency (NT) is often larger in a fetus with Down syndrome. Measurement of the crown-rump length (CRL) of the fetus is used to calculate the gestational age of the fetus. The best time (taking into account the small size of the fetus) is having the scan between 13 weeks & 13 weeks 6 days. At this stage the fetal organs can also be examined.
THE PURPOSE OF THE 11-14 WEEK SCAN:
- To date the pregnancy accurately. This is particularly relevant for women who cannot recall the date of their last period, have an irregular menstrual cycle, or who have conceived whilst breastfeeding or soon after stopping the pill. We measure the size of the fetus and from this we calculate the expected date of delivery.
- To diagnose multiple pregnancy. Approximately 2% of natural conceptions and 10% of assisted conceptions result in multiple pregnancy. Ultrasound scanning can determine if both babies are developing normally and if the babies share the same placenta which can lead to problems in the pregnancy. In such cases it would be advisable to monitor the pregnancy more closely.
- To diagnose certain major fetal abnormalities. Some major abnormalities may be visible at this gestation, but a follow up scan at 20-22 weeks remains essential. Not all anomalies are detected at 11-14 weeks.
- Risk assessment forDowns syndrome and other more rare chromosomal abnormalities (Edward syndrome, Patau syndrome, Turner Syndrome and Triploidy) with nuchal translucency measurement.
PERSONALISED RISK FOR DOWNSYNDROME
Babies with Down syndrome and heart failure tend to have extra fluid at the back of the neck (arrow).
Only sonographers with the “Certificate of Competence from the Fetal Medicine Foundation in London” are provided with the Computer Evaluation Programme to
perform this Down syndrome risk assessment.
Each woman will be given an estimate of her individual risk for Down syndrome in this pregnancy.
This is calculated by taking into account the age of the mother, measurement of two hormones in the mother’sblood and the scan findings. This test can detect about 90%-95% of fetuses with Down syndrome.
THE FACTORS ASSESSED AT THE 1ST TRIMESTER NT SCAN ARE SUMMARISED AS
- Age of the mother
- Amount of fluid behind the neck of the fetus (nuchal translucency)
- Presence or absence of the fetal nasal bone
- Fetal heart rate
- Blood flow through the tricuspid valve of the fetal heart
- Blood flow through the ductus venosus in the fetal liver
- Presence or absence of any major structural fetal abnormality
- Level of two hormones (free ß-hCG and PAPP-A) in the mother’s blood
WHAT IS DOWNS SYNDROME?
The term ‘syndrome’ is used to describe a collection of features which are often seen together. Down syndrome was first identified by Dr John Langdon Down in 1866, who noticed a similarity in appearance in some of his patients. These individuals possessed a broad, flat face, a thick tongue and a small nose and were intellectually impaired to a variable degree.
However, there are more differences than similarities between people with Down syndrome. Many babies with the condition will have one or all of the following features at birth: low muscle tone (a floppy baby), a face that appears flatter with eyes slanting upward, small ears and a wider neck than usual, a crease across the palm of the hand and a gap between the toes. Some may have heart problems. While intellectual disability is a feature of the syndrome, those with the condition will develop and learn throughout life, but at a slower pace than usual.
There is no cure for a child born with this condition but many symptoms can be treated and special early intervention programs are enabling these individuals to develop their potential. A child with Down syndrome can usually do most things that any young child can do such as walking, talking, dressing and being toilet trained although they may do these things later than other children.
In each human cell, except for the egg and sperm cells, there are 46 chromosomes, made up of 23 pairs. The chromosomes are numbered according to their size. When egg and sperm cells are formed the number of chromosomes they contain is halved to 23 with only one copy of each pair. A baby is formed when the sperm from the father fertilises the egg from the mother. The baby will now have 46 chromosomes, just like the parents, with one copy from each parent.
Sometimes, when the egg and sperm are forming, a mistake occurs so that the chromosome pairs do not separate in an ordered fashion. The result is an egg or sperm cell that has only 22 chromosomes while others have 24 chromosomes. If an egg or sperm carrying 24 chromosomes combines with an egg or sperm carrying the usual 23 chromosomes, the result will be an individual with cells in which there are 47 chromosomes instead of the usual 46. Thus there will be three copies of a particular chromosome in the cells rather than two.
Down syndrome is caused by an extra copy of chromosome number 21. For this reason it is also known as Trisomy 21. The presence of the extra chromosome causes the mental and physical characteristics of Down syndrome. In 95% of cases the extra chromosome is present in all the cells of the baby. In about 1% of cases, some of the baby’s cells will contain the usual chromosome number of 46 and others will contain the extra chromosome 21. This situation is known as ‘mosaic’ Trisomy 21. In about 4% of cases, the extra copy of chromosome 21 is attached (translocated) to another chromosome. This is called ‘translocation’ Trisomy 21. This type of Downs syndrome can be inherited. So where there is a previous child with Down syndrome or a close family history of Down syndrome, a discussion with a genetic counsellor can provide information about the risk of having an affected child and the availability of testing.
DOWN SYNDROME RISK
WHO IS AT RISK OF HAVING A CHILD WITH DOWNS SYNDROME?
The extra chromosome 21 can come from either the egg or the sperm. However the chance of having a baby with Down syndrome increases with a woman’s age. Table 1 shows the age-related risks of chromosomal problems occurring in a pregnancy. It is estimated that 1 in 3-4 fertilised eggs are chromosomally abnormal and this increases with the mother’s age. Therefore, most people have had at some time, a chromosomally abnormal conception which may have miscarried or not even been recognised as a pregnancy because the miscarriage occurred so early.
Table 1:Approximate risks of chromosomal changes associated with maternal age
|Maternal age at delivery||Chance of having a live-born baby with a Down Syndrome||Chance of having a live-born baby with a chromosomal abnormality|
|20-24 years||1 in 1478||1 in 506|
|30 years||1 in 909||1 in 385|
|31 years||1 in 900||1 in 385|
|32 years||1 in 750||1 in 323|
|33 years||1 in 625||1 in 286|
|34 years||1 in 500||1 in 244|
|35 years||1 in 384||1 in 179|
|36 years||1 in 307||1 in 149|
|37 years||1 in 242||1 in 124|
|38 years||1 in 189||1 in 105|
|39 years||1 in 146||1 in 81|
|40 years||1 in 112||1 in 64|
|41 years||1 in 85||1 in 49|
|42 years||1 in 65||1 in 39|
|43 years||1 in 49||1 in 31|
|44 years||1 in 37||1 in 24|
|45 years||1 in 28||1 in 19|
The only way to know for sure whether or not the fetus has a chromosomal abnormality is by having an invasive test such as chorionic villus sampling (CVS) or amniocentesis (amnio). However, these tests carry a risk of miscarriage of about 1-2%.
It is up to you and your partner to decide whether or not the risk of the fetus having a chromosomal abnormality is high enough to warrant having an invasive test. As a guideline, an invasive test is usually offered if the risk of Down’s Syndrome is 1 in 100 or above.
The most accurate way of estimating the risk of the fetus having Down’s Syndrome is carried out at 11-13 weeks and depends on the:
- Age of the mother.
- Amount of fluid behind the neck of the fetus (nuchal translucency).
- Presence or absence of the fetal nasal bone.
- Fetal heart rate.
- Blood flow through the tricuspid valve of the fetal heart.
- Blood flow through the ductus venosus in the fetal liver.
- Presence or absence of any physical abnormalities.
- Level of two hormones (free ß-hCG and PAPP-A) in the mother’s blood. The blood test needs to be done after the scan.
After the scan, on the basis of all the above factors, the estimated risk for Down’s Syndrome will be discussed with you. Only you can then decide if you wish to have an invasive diagnostic test.
Irrespective of whether or not you decide to have an invasive test, it is recommended that you have a scan at 20 weeks to check for physical abnormalities.
For many couples, the 21 week detailed anatomy scan can be one of the highlights of a pregnancy. It is a wonderful opportunity to see the actual form and movements of the fetus. During the scan a specialist sonographer will measure the fetal size, examine each part of the fetal body, determine the position of the placenta and assess the amount of amniotic fluid. Special attention is paid to the brain, face, spine, heart, stomach, bowel, kidneys and limbs.
Whatever your 1st trimester NT scan shows, it is recommended that you have a detailed anatomy scan to confirm normal fetal growth & development between 13 weeks and 21 weeks. In pregnancies where the NT (nuchal translucency) measurement was increased, or following infertility treatment or in high risk pregnancies (such as twin pregnancies or maternal diabetes), we will also perform a more detailed heart scan (echocardiography).
Should any fetal abnormality be detected the significance of the findings will be discussed and the parents will be given the opportunity to have further counselling. Many families are surprised at how much can be seen at this scan. Ultrasound is able to show the anatomy that lies within your baby including the brain, stomach, heart, kidneys, bladder, to name a few. Because each part of the fetus is carefully examined, this scan can take from 30 minutes to an hour.
WHY IS THE SCAN DONE?
This is a routine examination performed at 20-22 weeks and should be offered to all pregnant women in India. In our practice the vast majority of patients have had a 11-14 week scan which has already determined the number of babies present, estimated due date and risk of Downs Syndrome and early anomaly scan.
The scan at 20-22 weeks is more to assess:
- Fetal structural (morphological/organ) development.
- Early fetal growth
- Placental position
- Amniotic fluid volume
- Cervical length
- Screening for pre-eclampsia (high blood pressure in pregnancy)
WHAT PART OF THE BABY WILL BE SEEN?
You will notice a dramatic difference in the anatomic detail visible in your baby on this scan when compared to the 12 week scan.
The ultrasound will endeavour to evaluate the fetal brain, face, spine, heart, lungs, stomach, kidneys, bladder, cord insertion at the belly button, arms and legs, placenta cervix and amniotic fluid.
CAN ALL ABNORMALITIES BE SEEN?
An amazing amount of detail can often be seen. However it is important to realize that not all parts of the baby show up well with ultrasound. No ultrasound examination can ever guarantee a normal fetus. The best centres in the world consistently report on the limitations of ultrasound and its inability to detect all fetal abnormalities.
Up to half the fetal heart defects will not be seen. Some of these are only minor, but some may not be apparent until the fetus is bigger, later in the pregnancy. Many bone growth problems, forms of dwarfism, will only be possible to be suspected late in pregnancy and the diagnosis is made on x-rays taken after the baby is born.
WHAT ABOUT DIAGNOSING DOWN SYNDROME?
Down syndrome is a problem whereby every cell in the body has an extra chromosome 21. There is no specific diagnostic finding on ultrasound. It is necessary to look at fetal cells down a microscope to diagnose a chromosomal abnormality. Hence, chromosomal lesions such as Down syndrome, cannot be diagnosed with ultrasound. Some 40% of Down syndrome fetuses will appear normal on the 20-22 week scan. Sometimes, there may be some ultrasound findings which can make us suspicious of an increase chance that the fetus has a chromosome lesion. However, noninvasive ultrasound screening for chromosome lesions is best done at the 11-14 week scan.
ARE THERE ANY SERIOUS ABNORMALITIES NEVER SEEN?
Conditions such as cerebral palsy, blindness, deafness, autism and most skin and soft tissue lesions are never detected with ultrasound. The fetal position and size of the maternal abdomen are important factors that affect fetal anomaly detection.
It is better if your bladder is not emptied just before the scan as it helps push the uterus above your pubic bone and generally makes the scanning more technically satisfactory. We don’t require your bladder to be uncomfortable.
CAN I BRING MY PARTNER OR SUPPORT PERSON?
Husbands or partners are always welcome in the ultrasound room. Family members & children are not allowed into the examination room. This is because they are distracting to the sonographer, and the scan may take anything from 30-60 minutes. They are welcome to join in the last 5 minutes of the examination when everything has been checked.
IS ULTRASOUND SAFE?
Ultrasound has been used throughout the developed countries all over the world for the past 30- 40 years and no significant harmful effects of obstetric ultrasound have been shown. It is considered safe.
WHAT IF AN ANOMALY IS FOUND?
We understand that this a very difficult time for the patients and their families. with the necessary counselling and support in collaboration with the referring obstetrician/general practitioner, paediatric specialists and geneticists to offer the parents and the unborn fetus the best treatment available in India. In some cases intrauterine procedure are carried out for treatment of anomalous fetus.
Fetal echocardiography is a test similar to an ultrasound. This exam allows your doctor to better see the structure and function of your unborn child’s heart. It’s typically done in the second trimester, between weeks 18 to 24.
The exam uses sound waves that “echo” off of the structures of the fetus’ heart. A machine analyzes these sound waves and creates a picture, or echocardiogram, of their heart’s interior. This image provides information on how your baby’s heart has formed and whether it’s working properly
Interval Growth Scan
WHY DO I NEED A SCAN IN THE THIRD TRIMESTER?
Your obstetrician may refer you for a scan in the third trimester if you:
- Are clinically too large or too small for dates.
- Have vaginal fluid loss.
- Have a low-lying placenta on 18-20 week scan.
- Have premature contractions.
- Had a small baby in the past.
- Have high blood pressure.
- Have diabetes or other medical conditions.
- Have pain in your abdomen.
- Have twins/multiple pregnancy
This scan aims to determine the growth and health of the fetus by:
- Measurement of the size of the fetal head, abdomen and thigh bone and calculation of an estimate of fetal weight.
- Examination of the movement of the fetus.
- Evaluation of the placental position and appearance.
- Measurement of the amount of amniotic fluid.
- Assessment of blood flow to the placenta and fetus by colour Doppler ultrasound.
CAN I SEE BABY IN THE SAME DETAIL AS THE 18-20 WEEK SCAN?
Some parts of the fetus become harder to see as the baby occupies much more space in the uterus, so in general we cannot see much of the baby as well as on earlier scans. Things like the fingers and toes, hands and feet are often wedged away out of sight. The further into the pregnancy we go the thicker the skull bones become which can shadow and obscure the fetal brain detail. We do however see some things better such as the face and heart. This always depends on what position the baby is in and how co-operative the fetus wants to be for us. If there is enough fluid in front of the fetal face we may be able to get a 3D or 4D image for you.
HOW IS THE FETAL WELL-BEING ASSESSED?
Ultrasound forms a major tool in the assessment of the current fetal health by Doppler assessment. Other assessments include the clinical history and examination and cardiotocography (CTG) assessment. The placental function can also be assessed by examining the blood flow through the umbilical cord artery. The severity of increasing resistance to flow will be reflected in the cord Doppler readings showing high waveforms to more severe changes of absent or reversed flow in the artery during cardiac relaxation (diastole). Flow in the brain arteries and in the liver veins also help give an overall assessment of the current state of fetal well being.
A Doppler is a form of ultrasound scan that helps to assess your baby's health. It measures the blood flow in different parts of your baby's body, such as his umbilical cord, brain and heart. This helps to show whether he's getting all the oxygen and nutrients he needs via the placenta.
A Doppler scan can be performed at the same time as a normal ultrasound and uses the same equipment. Most ultrasounds have a Doppler function. The person carrying out the scan (sonographer) will put some gel on your tummy and move a hand-held device (transducer) over your skin.
a. Placental Doppler
The placenta is a two compartment nutrient, fluid and gas exchange organ:
- The maternal compartment is assessed by uterine artery Doppler
- The fetal compartment is assessed by umbilical artery Doppler
- Uterine arteries: Increase in diastolic flow with loss of the early-diastolic notch
- Umbilical arteries: Appearance of end-diastolic velocity
- Decline in pulsatility index in both vessels
In abnormal placentation there is:
- Impaired trophoblastic invasion of the maternal spiral arteries resulting in high uterine artery pulsatility index and persistence of the uterine artery notch
- Abnormal villous vascular tree resulting in abnormal waveform in the umbilical arteries which depends on the degree of impaired vasculature:
- 30% impairement results in high pulsatility index
- 50% impairement results in absent end-diastolic velocity
- 70% impairement results in reversed end-diastolic velocity
The risk for hypoxemia / acidemia is proportional to the decrease in umbilical end-diastolic flow.
b. Ductus venosus
The ductus venosus is the primary shunt regulating nutrient flow to the liver and heart
The vessel can be imaged in a saggital or abdominal transverse view
- In normal fetuses the a-wave is positive from the first trimester onwards and the pulsatility index for veins decreases with advancing gestation
- High pulsatility index for veins and absent or reversed a-wave are observed in fetuses with aneuploidies, cardiac defects, growth restriction and either the recipient or donor fetus in twin-to-twin transfusion syndrome
c. Middle cerebral artery
The middle cerebral artery (MCA) is a branch of the circle of Willis in the base of the skull
A transverse section of the fetal head is obtained and color flow mapping is used to identify the circle of Willis and the MCA. The pulsed wave Doppler gate is then placed on the proximal one-third of the MCA. The angle of insonation should be zero degrees. Attention should be taken to avoid any unnecessary pressure on the fetal head because this increases both the peak systolic velocity (PSV) and pulsatility index (PI).
- In normal pregnancies the PSV increases and the PI decreases with gestation
- Decreased PI is observed in fetal hypoxemia and fetal hypertension
- Increased PSV is observed in fetal anemia and fetal hypercapnia (increased paCO2)
3D / 4D Scan
3D ultrasound is revolutionising the enjoyment and clinical efficacy of obstetric imaging. Although first described in 1961, three dimensional imaging has undergone dramatic improvements in technology over the past 5 years. Such that 3D and “real time” or “live” 3D or 4D ultrasound is available at the push of a button.
CAN I ALWAYS GET A GOOD IMAGE OF MY BABY’S FACE?
It would be hoped that we could get some 3D images of the baby but it is difficult to guarantee getting good images on every babies face. At 20 weeks there is little soft tissue or flesh on the babies cheeks, so usually the face images are better later in the pregnancy, often in the third trimester. There needs to be a reasonable amount of fluid in front of the babies face for the 3D images to be ideal. Also many babies may not be very cooperative on the day and often hide behind their hands or even feet. If they are hiding their faces then it is difficult to photograph them. Some just hate the paparazzi!
ARE THERE ANY RISKS WITH 3D OR 4D ULTRASOUND?
No, there are no known side effects of medical ultrasound on the mother or fetus.
WHAT ARE THE ADVANTAGES OF 3D AND 4D ULTRASOUND IN PREGNANCY?
- Rapid acquisition of volume data.
- Improved identification of suspected or detected anomalies.
- More accurate identification of the extent and size of anomalies not seen with 2D static scanning.
- Improved recognition of anomalies by non-ultrasound clinicians.
- Improved comprehension/understanding of fetal anatomy by the patient and family.
- Improved maternal/paternal bonding.
- We do 4D scans at 26 weeks for family bonding.
DIFFERENT TYPES OF TWINS
1. DICHORIONIC DIAMNIOTIC (DCDA) TWINS:
DCDA twins have 2 placentas and 2 separate sacs. These babies usually have different genetic material and only 10% will be identical.
2. MONOCHORIONIC DIAMNIOTIC (MCDA) TWINS:
MCDA twins have a single placenta and 2 separate sacs. These babies have identical genetic material
3. MONOCHORIONIC MONOAMNIOTIC (MCMA) TWINS:
MCMA twins have a single placenta and both babies are moving around within the same sac. They also have the same genetic material.
Amniocentesis is a prenatal test that allows your healthcare practitioner to gather information about your baby's health from a sample of your amniotic fluid. This is the fluid that surrounds your baby in the uterus.
The most common reason to have an "amnio" is to determine whether a baby has certain genetic disorders or a chromosomal abnormality, such as Down syndrome.
Just like chorionic villus sampling (CVS), a procedure done in the first trimester, amniocentesis produces a karyotype – a picture of your baby's chromosomes – so that your caregiver can see for sure if there are problems. (In about 1 percent of cases, there's a problem with the specimen and the test doesn't yield a result.)
Amniocentesis is usually done when a woman is between 16 and 20 weeks pregnant. Though all women should be offered the option of having an amnio, women who choose to have this test are often those at increased risk for genetic and chromosomal problems, in part because the test is invasive and carries a small risk of miscarriage.
Here are a few other reasons that amniocentesis may be done:
• To diagnose or rule out an intrauterine infection
• To check on the well-being of your baby if you have a blood sensitization, such as Rh sensitization. This is a complex condition that can occur if your blood is a different type than your baby's. (Note: Obstetricians are increasingly using Doppler ultrasound for this purpose instead of amnio.)
• To assess the maturity of your baby's lungs when considering an early delivery for medical reasons (unless it's clear the baby needs to be delivered immediately regardless of lung maturity)
Chorionic Villi Biopsy
Chorionic villus sampling (CVS), also known as chorionic villus biopsy, is a prenatal test that diagnoses chromosomal abnormalities such as Down syndrome, as well as a host of other genetic disorders. The doctor takes cells from tiny fingerlike projections on your placenta called the chorionic villi and sends them to a lab for genetic analysis.
CVS and another test called amniocentesis produce a karyotype – a picture of your baby's chromosomes – so that your caregiver can see for sure if there are any problems.
Women who choose to have CVS or amniocentesis are often those at increased risk for genetic and chromosomal problems, in part because these tests are invasive and carry a small risk of miscarriage.
The main advantage of CVS over amniocentesis is that you can have it done earlier — generally between 10 and 13 weeks of pregnancy. For an amnio, you'll have to wait until you're at least 16 weeks pregnant.
Many parents look forward to their 21 week anatomy scan, only to discover that the doctor sees a ‘soft marker’ in the fetus. Soft markers are not abnormalities but are anatomical variants. For example, an anatomical ‘variant’ is having a crooked little finger or gap between big toe and second toe —having these variants does not mean you are physically abnormal. In fact, 10-15% of all babies have at least one soft marker. Most of the time, the finding of a soft marker in an otherwise normal-appearing baby is a big to-do about nothing. But in rare cases, they can be a clue that a larger problem exists, such as Down syndrome or other serious abnormalities. But before you panic, understand that even if you are told your baby has a soft marker, the chances are more than excellent that everything is fine.
The bottom line is that generally, in an otherwise low risk pregnancy with a normal first trimester screening test, the presence of a soft marker or two does not significantly increase the odds that your baby has a problem and more invasive testing with amniocentesis is not usually warranted. If you are already high risk such as being over 35 or the baby has other anatomical abnormalities, your doctor will advise you as to whether or not amniocentesis is an appropriate next step.
The following is a list of some Soft Markers:
- Choroid plexus cysts:These are round cystic structures seen in the part of the brain that makes the cerebral-spinal fluid. Cysts in the brain sound scary, but they have no significance to the development and intelligence of your baby. They are significant in that 30% of babies with Edward syndrome (trisomy 18) have them together with other defects that we can recognise on ultrasound. However, keep in mind, very few babies with choroid plexus cysts have Edward syndrome!
- Borderline ventriculomegaly:In the brain, the lateral ventricle is a structure which holds some of the cerebrospinal fluid. It is routinely measured on every anatomy scan to look for hydrocephalus or ‘water-on-the-brain”. If it is above the normal range, it may be associated with a host of problems. If this is found, your doctor will likely do some additional testing and follow-ups just to make sure it doesn’t represent a problem or worsen.
- Echogenic focus in the heart:Fancy words for a ‘bright spot’ in the heart which represents some calcification or prominence to the tiny heart muscle. This is a relatively common finding on ultrasound. They do not affect the function of the muscle or the beating of the heart. It is seen in approximately 20% of all Down syndrome fetuses, usually in association with other findings on ultrasound.
- Echogenic Bowel:Sometimes there can be very bright spots seen within the baby’s abdomen or liver. Most of the time, this represents nothing but in some cases, it may be caused by Down syndrome, cytomegalovirus (CMV), or cystic fibrosis. A few normal babies with echogenic bowel will show poor growth later in the pregnancy so your doctor might recommend follow-up growth scans.
- Single umbilical artery: The normal umbilical cord contains 3 vessels (2 arteries & 1 vein). Sometimes, there is only one artery and one vein. Again, most of the time, this is just a normal variant and the baby is born healthy and well. However, in some cases, 2 vessel cords can be associated with kidney or heart abnormalities and/or poor growth. A careful look at the anatomy will be performed to rule out any associated defects. Additional ultrasounds will likely be done to monitor fetal growth.
- Mild pyelectasis:This occurs when there is fluid within the part of the kidney that collects urine. A little bit of fluid (less than 4 mm) is perfectly normal. More than that has been loosely correlated with Down syndrome. Even if Down syndrome is not suspected, the chances are you will have follow-up ultrasounds to keep track of the amount of fluid. In some cases, the amount of the fluid can increase and signal a urinary blockage or other problem with the kidney or bladder. Again, these follow-ups can be nerve-wracking but most of the time, even if the kidneys continue to retain fluid, it can be medically managed and successfully treated after the baby is born.
- “Sandal gap” toes:a larger-than-usual gap between the first and second toes can be associated with Down syndrome.
- Clinodactyly:a pinky finger that curves slightly toward the ring finger may be associated with Downs syndrome.A diagnostic test can confirm or exclude all chromosomal defects related to soft markers such as Down syndrome, Edward syndrome etc. These procedures, usually an amniocentesis, carry a small risk to the pregnancy (1:400 or 0.25% risk of miscarriage). A diagnostic procedure is only done when parents feel that the chance of a fetal abnormality for them, justifies this small risk.
Irrespective of whether or not you decide to have an invasive test, it is recommended that you have a scan at 21 weeks to check for physical abnormalities.
2D, 3D & 4D SCANS
WHAT IS AN ULTRASOUND / SCAN?
A pregnancy ultrasound or scan, is an imaging test that uses sound waves to see how a baby is developing in the womb. These scans are used during the course of the pregnancy to monitor fetal growth and development. Ultrasound waves cause no harm to the mother or fetus.
There are two types of ultrasound examinations:
A small ultrasound probe is inserted into the vagina and rests on the cervix to create an image of the early 6-12 week pregnancy and the maternal pelvic organs (uterus and ovaries).
The ultrasound probe is placed on the lower abdomen to examine the larger uterus containing fetus, placenta & amniotic fluid, in a pregnancy from 12 weeks onwards.
WHY ARE SCANS PERFORMED IN PREGNANCY?TO:
- Diagnose an intra-uterine pregnancy.
- Diagnose a miscarriage.
- Determine presence of multiple fetuses.
- Diagnose normal fetal & placental development.
- Diagnose birth defects.
- Assist in prenatal tests such as an amniocentesis.
- Determine size and position of a fetus late in the pregnancy.
Are all scans the same?
Some things are looked at in every scan, others relate to pregnancy duration & fetal size. Every scan should document the number of fetuses, the fetal heart beat, the size of the fetus and development of the fetal organs. The scan will also check the position of the placenta (afterbirth) and the amount of fluid around the fetus (amniotic fluid). This will always be done using 2D scans.
While measuring and examining the fetus, one can sometimes detect the development of structural abnormalities in the fetus. Fortunately most fetuses are normal but in about 5% an abnormality is present. Some defects are minor, others severe or fatal. Not all parents want to know before the birth whether their fetus is normal or not because they may feel too upset when a problem is detected many weeks before the birth. This can be very distressing to parents. To look for abnormalities in the fetus is therefore optional. If you don’t want to be informed about any abnormal findings in the fetus, you must tell the person examining you before the scan is started.
DO I NEED A FULL BLADDER?
The shape of the modern probes means that the scan can be done with an empty bladder. Try not to drink too much fluid prior to the scan.
CAN I BRING FAMILY TO SEE THE ULTRASOUND?
Husbands or partners are always welcome in the ultrasound room. Family members & children are not allowed into the examination room. This is because they might be a distraction to the sonographer and the scan may take anything from 30-60 minutes. They are welcome to join in the last 5 minutes of the examination when everything has been checked.
2D,3D & 4D SCANS 2
WHAT IS A 2D SCAN?
Despite all the buzz about 3D images of the baby, where it looks like a ‘real’ baby, your ultrasound examination must be done in 2D (dimension). This is because 2D is still the only way for the doctor and sonographer to see the structures below the baby’s skin, looking inside the baby, at the anatomy.
It helps you to understand what the various shades of white, grey and black represent. On ultrasound, fluid is black and you can see the baby moving around in the amniotic fluid. There are areas of black within the baby as well which include the brain, the blood in the heart and blood vessels. Any white you see is bone and cartilage. The different shades of grey represent different densities of soft tissue such as the placenta, muscles, liver and other organs within the baby.
WHAT IS 3D & 4D ULTRASOUND?
Those beautiful pictures that you see in magazines are known as 3D ‘surface rendered’ images. In other words, the ultrasound machine uses sophisticated software to construct an image of the baby as you would see it ‘with the skin on’. The technology is similar to that used to make animated cartoons like Shrek, so that the image you see on the ultrasound monitor is really a computer-constructed image, not a true peek at the baby itself. In order to get a beautiful 3D ultrasound image, the baby’s face must not be covered by hands or touching anything. Just like any picture, if the baby isn’t looking at the ‘camera’, you can’t get a good image. When the baby’s face is clear, the image can be astounding. But, if the hands, the cord, or something else is blocking the view, we can’t get that gorgeous shot like in the promotions. Don’t count on getting a great image every time.
4D is simply a series of single 3D images so that there is the appearance of motion. The 4th dimension is time. The important thing to remember when you look at any 3D/4D image is that it is a computer-constructed image, not a glimpse at the real thing. As such, the computer can make some odd assumptions as it is trying to render a realistic surface to the baby and weird bulges and lumps appear. 4D scans are used in the detailed examination of the heart, fetal echocardiography.
WHAT ARE THE LIMITATIONS OF 3D & 4D SCANS?
Remember that the 3D/4D is more of a fun tool than it is diagnostic. The medical use of 3D scans is to examine problems in the fetus such as cleft lip or masses. The advantage of 4D scanning is in examination of the fetal heart (echocardiography)– a moving structure. So detailed 3D and 4D scans are especially useful in high risk pregnancies.
The best time to get a good 3D picture scan of the face is around 27 to 30 weeks. At this point, the baby has begun to put on some body fat and looks more like it will at birth. This is also the time when it is most likely that you can get an unobstructed view of the face. After 30 weeks, the baby’s head usually becomes wedged down in the mother’s pelvis which is great for giving birth, but not great for seeing the face.
CARDIAC SCAN- FETAL ECHOCARDIOGRAPHY
Fetal echocardiography is a detailed ultrasound examination of the fetal heart performed by specialist sonographers and in consultation with a paediatric cardiologist when needed. We use 2D images to examine the chambers and blood vessels of the heart; Doppler to check the valves; colour Doppler to examine the blood flow in the heart and blood vessels; 3D imaging to reconstruct multiple planes; and 4D imaging or cine looping to examine cardiac motion & function
Heart abnormalities affect 1:100 babies. The vast majority of cardiac abnormalities (75%) can be detected at 20-22 weeks by sonographers trained in fetal cardiac scanning. We offer this scan as part of the routine 20-22 week scan, but especially recommend this scan for women with:
- a family history of heart abnormalities,
- previous baby affected by a heart abnormality,
- where increased nuchal translucency had been found at the 11-14 week scan.
- Maternal diabetes
- Fetal arrhythmia (abnormal cardiac rhythm)
- Maternal lupus
- A fetus with noncardiac abnormalities
- A fetus with a chromosomal abnormality