Why do an ultrasound between the eleventh and fourteenth week?
To establish the gestational period
In some cases, the exact date of the last menstruation is not remembered. Or the periods are irregular, or maybe the woman is breastfeeding.
By measuring the length of the fetus (CRL), the gestational period and the presumed date of delivery are known.
To diagnose twin pregnancies
The incidence is 2% in spontaneous pregnancies and 10% in assisted ones. Ultrasound reveals whether the twins are monochorionic (one placenta) or dichorionic (two placentas).
Monochorionic twins may be at risk and a strict pregnancy follow-up and protocol is recommended.
To diagnose an early miscarriage
Unfortunately, the incidence of spontaneous abortion at this time is about 5% and often the diagnosis is purely ultrasound without any reported symptoms.
For the diagnosis of some fetal anomalies
In 1% of pregnancies, the fetus is affected by anomalies. Some of these can be diagnosed on ultrasound at 11-14 weeks.
To establish the risk of Down pregnancy
or other chromosomal abnormalities
Any woman, regardless of her age, has a risk of giving birth to a child with a chromosomal abnormality, such as Down syndrome.
The computerized assessment of the pregnant woman’s age with some ultrasound-detectable parameters (nuchal translucency, presence or absence of the nasal bone, blood flow through the fetal heart) and some hormones present in the maternal blood allows a diagnosis of Down syndrome in 90% of cases.
But this test cannot be considered a substitute for CVS or amniocentesis which are the only way to identify a chromosomal abnormality with certainty.
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