The important scans during the antenatal period are the
- 1. 11 – 13+6 weeks (NT scan)
- 2. Anomaly scan (TIFFA scan)
- 3. Interval growth scan
- 4. Fetal well being scan with fetal dopplers
- 5. Fetal echocardiography
- 6. 3D ultrasound imaging
11 – 13+6 weeks (NT scan)
Measurement of Nuchal translucency and assessing risk for Downs syndrome and other chromosomal abnormalities
Diagnose certain fetal structural anomalies.
This scan can also help in diagnosing multiple gestations, early pregnancy failure and in accurate dating of pregnancy.
Following this scan the couple will receive counseling including the significance of the risk and the various options that are available for further testing.
This scan is usually done between 18-23 weeks. Detailed study of fetus is done during this scan where each and every part of the fetus imaged using the “Rule of 3”. In case any abnormality is detected, the significance will be discussed by the Fetal medicine specialist and if needed the couple will be referred to other specialists for counseling.
Interval growth scan
This scan is usually done between 28-30 weeks to assess the fetal growth more so in women who have developed or who are at potential risk of developing hypertension or diabetes in pregnancy.
Fetal well being scan with fetal dopplers
This scan is done between 34-36 weeks to assess the health and the well being of the fetus and assessment of blood flow to the placenta and fetus by color Doppler ultrasonography in certain indicated cases.
Though a basic examination of the 4 chambers of the heart and connecting vessels are done during the TIFFA scan, a detailed fetal echocardiography scan is recommended for women with family history of heart abnormalities or if a previous child is affected or an increased nuchal translucency was observd in NT scan with normal chromosomal study. It is also recommended for a pregnant woman with altered glycemic status.
3D ultrasound imaging
Provides a more detailed evaluation for certain parts of the fetal anatomy for suspected fetal abnormalities such as cleft lip, cleft palate and spine abnormalities (i.e. spina bifida). A good 2 D scan is an important prerequisite for 3 D scan. Not all centres will perform the 3D imaging.
Frequently Asked Questions
1. What is ultrasound scanning? Is it safe for the mother and the baby?
Sound waves which we can hear are in the range of 20Hz to 20KHz. Electro-magnetic waves in the frequency range of 2MHz to 12MHz are called ultrasound waves, shriller than normal sound waves. Ultrasound waves are absorbed/reflected by body tissues depending upon their type. In ultrasound scanning, a probe emits ultrasound waves directed at the body being examined and a detector captures the reflected waves. Based on the intensity of the received waves, an image of the tissue under examination is created.
Ultrasound scanning is a non-invasive procedure. It is a simple procedure conducted on the examination table. Unlike X-rays which are contra indicated during pregnancy, ultrasound scanning is safe for the mother and the growing fetus. Repeated ultrasound scans pose no problems to either the mother or the fetus.
A jelly like substance, the ultrasound gel, is applied on the surface to create a good transmission medium between the probe and the human body. It is mostly composed of water and is totally harmless to the patient. It might feel a little cold just when applied, but it is in no other way uncomfortable. After the procedure, the gel is wiped with tissue paper.
2. Sometimes patients are asked to take in lot of water and not pass urine before ultrasound scanning. Why is this?
The female reproductory organs are positioned in the body in such a way that when the bladder is full, ultrasound waves get conducted through the water filled bladder and provide a clear imaging of the organs. In the absence of the water in the bladder, ultrasound waves get diffused and imaging becomes difficult. Hence patients are asked to come with a “full bladder”.
3. Why do patients experience delays in appointments for ultrasound scanning?
The doctor has to take images at several critical positions of the fetus to take measurements so that she can assess the well being of the fetus. A fetus is in its own world in the mother’s womb and many times it does not keep still to enable such measurements. Taking critical sections, therefore consumes a lot of time of the doctor. In some extreme cases, appointments might be rescheduled because the fetus might never present itself in the right position to be scanned. This behavior of the fetus is beyond the control of the doctor and this invariably results in delays.