The anomaly scan is the most common scan of the second trimester. It is done between the 18th and 20th week. An anomaly scan is also known as a mid-pregnancy scan. It helps look at the baby and the womb of the mother. The doctor will check whether the baby is developing normally and it also helps keep track of the position of the placenta.
Almost all scans during pregnancy are done abdominally. The ultrasound doctor applies gel to the abdomen and moves the transducer over it to obtain images of your baby. As sound waves from the transducer bounce off from the baby's features or organs, images are formed on a computer screen. The doctor tries to get different views of the baby from different angles to get as much information as possible. When he/she gets a clear picture of the baby's organs or body parts, he/she will take measurements. You may be asked to get a transvaginal scan if your doctor wants any information about the cervix.
What do they look for during the scan?
1. While conducting the anomaly scan during the second trimester, the doctor looks at the following:
2. The number of babies present in the womb. Sometimes, twins are not found until 20 weeks into pregnancy.
3. The shape and structure of your baby's head. There is a possibility to detect brain problems, which are rare, at this stage.
4. Most importantly, there is a check the baby’s heart. The doctor takes a look at the four chambers. The upper two chambers and the atria, and the lower two chambers and the ventricles, should be equal in size. The valves should open and close with each heartbeat. The doctor will also look at the major veins and arteries, which carry blood to and from the heart.
5. The baby’s stomach is also observed. The baby sometimes swallows some of the amniotic fluid that he/she lies in, which is seen in the baby’s stomach as a black bubble.
6. The doctor will check whether your baby has two kidneys and whether urine flows freely into his/her bladder.
7. The baby’s face will also be checked for a cleft lip. Cleft palates inside a baby's mouth are difficult to detect at times.
8. The spine of the baby, both, transversely and longitudinally is looked at to make sure that all the bones are aligned.
9. The abdominal wall of the baby is cheked to make sure it covers all the internal organs at the front.
10. The doctors also take a look at the arms, legs, hands and feet of the baby to check for any deformities
In addition to the detailed study of the growth of the baby, the doctor also takes a look at the following:
a. The placenta
b. The umbilical cord
c. The amniotic fluid
The placenta may be on the front wall or the back wall of the uterus. It is usually near the top of the uterine wall. The placenta might reach down or cover the neck of the uterus. If the placenta is lying low in the uterus, the doctor may suggest for another scan in the third trimester to check its position. By then, the placenta should move away from the cervix.
The doctor will also count the three blood vessels (two arteries and a single vein) in the umbilical cord. They will check the amount of amniotic fluid and whether it’s enough for the baby to move freely.
In the scan, the doctor will measure the body parts of the baby and he/she will check the child’s physiological growth. The doctor will measure:
a. The head circumference (HC) and diameter (biparietal diameter or BPD)
b. The abdominal circumference (AC)
c. The length of the femur or thigh bone (FL)
Are there any risks?
Most scans show that the baby is developing normally and no problems are found.
If any problem is found or suspected, the doctor will suggest what has to be done. Although, all scans cannot detect all problems, and there is always a chance that a baby may be born with a health problem that scans could not detect. If the scan shows that there might be a problem, you may be suggested another test find out for confirmation.
It is important to go through all the scans as prescribed by the doctor. It is a very important step in pregnancy, not only for the baby but for the mother too. If there are any problems in the growth of your baby, it can be diagnosed and treated without wasting any time through a scan. This will lead to the delivery of a healthy baby.
For more information about scans during pregnancy click here.