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Obstetric ultrasound

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Obstetric ultrasonography is the most important development in obstetrics since the introduction of antibiotics.

Before ultrasound scans the practitioner's hands and tape measure were the only ways to assess the size and position of the fetus.

Clinical examination is inaccurate whereas ultrasound is both safe and accurate.

It is now possible to examine the fetus for a range defects such as cleft lip, skeletal dysplasias, major cardiac and renal and gut lesions.

NICE have issued guidance concerning timing of routine ultrasound scans during pregnancy (1,2)

  • gestational age assessment:
    • pregnant women should be offered an early ultrasound scan between 10 weeks 0 days and 13 weeks 6 days to determine gestational age and to detect multiple pregnancies. This will ensure consistency of gestational age assessment and reduce the incidence of induction of labour for prolonged pregnancy
    • crown-rump length measurement should be used to determine gestational age
      • if the crown-rump length is above 84 mm, the gestational age should be estimated using head circumference
  • Screening for structural anomalies
    • pregnant women should be offered an ultrasound scan to screen for structural anomalies, ideally between 18 +0 and 20+6 weeks' gestation

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