Ultrasound to detect abnormalities in pregnancy

November 28, 2018

Healthcaretoday, Sonography, Non-invasive medical imaging, Transvaginal ultrasound, Transabdominal ultrasound, First trimester, Ectopic pregnancies, Chromosomal abnormalities, Dr Raman Subramaniam, parenting, pregnancy,

By Dr Raman Subramaniam,
Consultant Obstetrician and Gynaecologist,
Fetal Medicine and Gynaecology
Centre, Kuala Lumpur.

Ultrasound, also known as sonography, is a non-invasive medical imaging technique that uses high frequency sound waves beyond the range of human hearing. These sound waves are emitted from a probe, which is placed on the abdomen or inserted into the vagina, and create images of the internal structures of the body.

Transvaginal and transabdominal ultrasound techniques
The frequency of the sound waves depends on the type of probe used, with transvaginal ultrasound having a higher frequency than transabdominal ultrasound. To ensure optimal imaging, a gel is applied to the area being scanned. The resulting image is displayed on a screen in black and white, with varying shades of grey.

2D, 3D, and 4D imaging technologies
In addition to traditional 2D imaging, there is also the option of 3D imaging, which provides a reconstructed image of the volume of the structure being scanned. Furthermore, 4D imaging offers real-time visualization of the structure, adding the dimension of time and allowing for the observation of moving structures like a developing fetus.

Ultrasound applications in pregnancy
Ultrasound plays a crucial role in early pregnancy, particularly in the first trimester (up to 12 weeks), by assessing the viability, growth, and number of fetuses. It can also detect intrauterine pregnancy and potentially identify ectopic pregnancies (those that occur outside the uterus, such as tubal pregnancies).

Screening for chromosomal abnormalities
At 11 to 13 weeks and six days, ultrasound can be utilized to screen for chromosomal abnormalities like Down syndrome by evaluating the nuchal translucency (skin at the back of the neck) and the presence of a nasal bone. During the second trimester, a detailed scan for fetal structural anomalies is typically performed between 18 to 22 weeks of gestation.

After this stage, ultrasound is generally not necessary unless there are concerns about fetal growth abnormalities. In such cases, blood flow studies of various fetal vessels can be conducted to determine the optimal time for delivery. If an abnormality is suspected, an invasive procedure like amniocentesis or placental biopsy may be performed under ultrasound guidance.

Limitations and risks of ultrasound imaging
While ultrasound is a valuable tool, it is important to note that fetal abnormalities can occasionally go undetected, even under the care of experienced professionals. Heart abnormalities, for example, can be subtle and may only be identified after the baby is born.

Some abnormalities, like ventriculomegaly (excessive fluid in the brain), can also develop abruptly, even if the 18 to 22 weeks scan appeared normal. Additionally, certain conditions such as a cleft palate at the back of the throat cannot be detected through ultrasound examination.

It is worth mentioning that routine 3D or 4D screening for fetal abnormalities is generally unnecessary, as the reconstructed images serve primarily as a visual experience for expectant parents. However, in specific circumstances, special modifications to the software can enhance the visualization of the fetus.

When abnormalities are detected through 3D screening, it aids parents in identifying the issue and seeking further counseling or therapy, while also fostering a stronger emotional connection with their unborn child.