Diagnostic Ultrasound

When and Why?

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The Diagnostic Ultrasound in Pregnancy
– Why & When is it Used?

Currently, ultrasound scan is considered to be a safe, non-invasive, accurate and cost-effective way to carry out investigations on the fetus.

Over the years of its use, ultrasound has become indispensable and plays a vital role in the care of all pregnant women.
Ultrasonography is mainly used in the following areas:

ultrasound diagnostic

1. Diagnosis and confirmation of early pregnancy.
From as early as four and a half weeks, the gestational sac can be seen, the yolk sac is visible at about five weeks. The embryo can be seen and measured at around five and a half weeks.

Ultrasound plays an important role in confirming that the pregnancy is within the cavity of the uterus.

2. Vaginal bleeding during early pregnancy.
In the event of vaginal bleeding during early pregnancy, the viability of the pregnancy can be established. Using a pulsed Doppler ultrasound, a heartbeat can be seen by about 6 weeks and is usually clearly visible by 7 weeks.

If this is visible, the likelihood of a continued pregnancy is more than 95 percent. Missed abortions or blighted ovum will normally give typical pictures of a deformed gestational sac and the absence of fetal poles or heart beat.

Fetal Heart Rate and Diagnostic Ultrasound

Fetal heart rate often varies with gestational age in the very early stages of pregnancy after getting pregnant. Normal heart rate at 6 weeks is about 90-110 beats per minute (bpm) and at 9 weeks is 140-170 bpm. At 5-8 weeks a bradycardia (less than 90 bpm) is linked to a high risk of miscarriage.

A large number of women do not ovulate at day 14, so findings from a single scan should always be interpreted with caution. The diagnosis of missed abortion is normally reached through a series of diagnostic ultrasound scans demonstrating lack of gestational development.

For instance, if an ultrasound scan shows a 7mm embryo but cannot demonstrable a clear heartbeat, a missed abortion may be diagnosed. In these situations, it is reasonable to repeat the ultrasound scan in seven to ten days to avoid any mistakes.
The timing of a positive pregnancy test can also be useful in this regard to assess the potential dates of conception.

A positive pregnancy test three weeks prior for example, would suggest a gestational age of at least 7 weeks. This information can prove useful for the interpretation of the scans.

In the case of first trimester bleeding, ultrasonography is extremely valuable for early diagnosis of ectopic pregnancies and molar pregnancies.

Check out the second part of this diagnostic ultrasound guide to learn even more!

Continue to Part 2

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