2 Why and when is Ultrasound used in Pregnancy?
Ultrasound scan is currently considered to be a safe, non-invasive, accurate and cost-effective investigation in the fetus. It has progressively become an indispensible obstetric tool and plays an important role in the care of every pregnant woman.
The main use of ultrasonography are in the following areas:
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1. Diagnosis and confirmation of early pregnancy.
The gestational sac can be visualized as early as four and a half weeks of gestation and the Yolk sac at about five weeks. The embryo can be observed and measured by about five and a half weeks. Ultrasound can also very importantly confirm the site of the pregnancy is within the cavity of the uterus.
2. Vaginal bleeding in early pregnancy.
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The viability of the fetus can be documented in the presence of vaginal bleeding in early pregnancy . A visible heartbeat could be seen and detectable by pulsed Doppler ultrasound by about 6 weeks and is usually clearly depict able by 7 weeks. If this is observed, the probability of a continued pregnancy is better than 95 percent . Missed abortions and plighted ovum will usually give typical pictures of a deformed gestational sac and absence of fetal poles or heart beat.
Fetal heart rate tends to very with gestational age in the very early parts of pregnancy. Normal heart rate at 6 weeks is around 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 associated with a high risk of miscarriage.
Many women do not ovulate at around day 14, so findings after a single scan should always be interpreted with caution. The diagnosis of missed abortion is usually made by serial ultrasound scans demonstrating lack of gestational development. For example, if ultrasound scan demonstrates a 7mm embryo but cannot demonstrable a clearcut heartbeat, a missed abortion may be diagnosed. In such cases, it is reasonable to repeat the ultrasound scan in 7-10 days to avoid any error.
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diagnosed. In such cases, it is reasonable to repeat the ultrasound scan in 7-10 days to avoid any error. The timing of a positive pregnancy test may also be helpful in this regard to assess the possible dates of conception. A positive pregnancy test 3 weeks previously for example, would indicate a gestational age of at least 7 weeks. Such information would be useful against the interpretation of the scans.
In the presence of first trimester bleeding, ultrasonography is also indispensible in the early diagnosis of ectopic pregnancies and moral pregnancies.
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