Dating scan

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After 13 weeks of gestation, the fetal age may be estimated using the biparietal diameter (the transverse diameter of the head, across the two parietal bones), the head circumference, the length of the femur, the crown-heel length (head to heel), and other fetal parameters.

Dating is more accurate when done earlier in the pregnancy; if a later scan gives a different estimate of gestational age, the estimated age is not normally changed but rather it is assumed the fetus is not growing at the expected rate.

In normal state, each body tissue type, such as liver, spleen or kidney, has a unique echogenicity.

The heartbeat is usually seen on transvaginal ultrasound by the time the embryo measures 5 mm, but may not be visible until the embryo reaches 7 mm, around 7 weeks' gestational age.The Late Dating Scan is a reassurance scan that takes place in the first couple of weeks of the second trimester.It provides information about the baby’s well-being.The baby is usually prepared to perform a little dance for the camera too!The sonographer will put some gel on your tummy and move a probe over the skin.

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