SCANS : ALL OR SOME?
I’ve had two scans already and just found out that my medical aid only pays for two. My next check-up is at 20 weeks, and apparently that scan is really important, so I’ll have to pay for it out of my own pocket. What happens at that scan that makes it such a big one? I wish I’d skipped the previous scan, just for finances’ sake.
DR KOLL ANSWERS: Scans are a very important part of antenatal care and, ideally, three to four scans should be performed during a low-risk pregnancy.
In a high-risk pregnancy, more frequent scanning will be required.
The first scan is performed at the first antenatal visit, ideally at around eight weeks from your last period.
This will firstly tell us that the pregnancy is in the womb and not an ectopic one.
Secondly it will confirm that the pregnancy is viable (alive) and will exclude early abnormalities.
Thirdly, it will give us an accurate assessment of the gestational age. Most women are usually reasonably sure of their last period but seldom do they know when they ovulated. For this reason, we quite often see a discrepancy between dates and sonar assessment of gestational age. Accurate assessment of the gestational age is essential to first trimester risk assessment for chromosomal abnormalities. This may also become very important later in the pregnancy if an early delivery becomes necessary or if the pregnancy progresses past the due date. Fourthly, it allows early diagnosis of multiple pregnancy (twins or triplets). There are two types of twins, those that share a placenta (monochorionic) and those that have their own placentas (dichorionic). This difference is vitally important to document early, as the further the pregnancy progresses, the more difficult it is to tell. The monochorionic twin pregnancy is a very high risk one that requires far closer monitoring and often very specialised care.
The early scan is often the only opportunity to distinguish the type of twin pregnancy with any certainty. Lastly, this scan allows us to look for any other abnormalities of the uterus and ovaries. These abnormalities may later become hidden by the growing uterus and foetus.
The second scan is performed between 11 and 14 weeks.
The main purpose of this scan is to look for signs of chromosomal abnormality. The findings at this scan together with blood tests and your age allow us to calculate the risk of the most common chromosomal abnormalities.
This scan also allows us to detect certain anatomical abnormalities in the foetus. It allows early assessment of the placenta and, by measuring the blood flows to the uterus, allows us to predict the risk of complications later in the pregnancy. The third scan is performed at around 20 weeks’ gestation.
The main purpose of this scan is to assess the anatomy of the foetus, literally from head to toe. The arms, legs, face, chest, abdomen and all the internal organs are checked.
It allows us to check that the foetus is growing appropriately.
It gives us another opportunity to look for subtle signs of chromosomal abnormality.
It allows us to assess the risk of the pregnancy ending prematurely.
It also allows assessment of the placenta and umbilical cord and blood flow to the uterus.
As can be seen from the above, all three scans independently give us valuable information, and all are important in assessing normality and future risk in the pregnancy. I would highly recommend that all of these scans be performed. A fourth scan in the third trimester is often helpful in assessing foetal growth and placental function.
More scans may be needed in high risk pregnancies. It is important to note that not all patients want this detailed assessment of their baby. If you do not wish to have any particular scan or any scans at all, it is your right to decline. ●