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. It is more common in boys than girls. 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.