Ultrasound in obstetrics IIIUltrasound in obstetrics III

By By

Dr. Khattab KAEODr. Khattab KAEO

Assis. Prof. of Obstetrics and Gynaecology Assis. Prof. of Obstetrics and Gynaecology Faculty of Medicine, Al-Azhar University, Faculty of Medicine, Al-Azhar University,

DamiettaDamietta

First trimester ultrasoundFirst trimester ultrasound

It was primarily implemented for dating It was primarily implemented for dating to improve interpretation of biochemi- to improve interpretation of biochemi- cal tests. Recently, it has been used to cal tests. Recently, it has been used to screen for fetal anomalies, detect chro-screen for fetal anomalies, detect chro-mosomal abnormalities and determine mosomal abnormalities and determine chorionicity in case of multiple pregn. chorionicity in case of multiple pregn.

Nuchal translucency (NT)Nuchal translucency (NT) It is an echo-free area at the back of the neck.It is an echo-free area at the back of the neck.Fluid collects behind the neck partly because the fetus Fluid collects behind the neck partly because the fetus

tends to lie on its back and partly because of the tends to lie on its back and partly because of the laxity of the skin of the neck. laxity of the skin of the neck.

Originally, 3 mm thickness was chosen as the cut-off Originally, 3 mm thickness was chosen as the cut-off level; recently, however, a percentile for gestational level; recently, however, a percentile for gestational age was developed and the 9th percentile for gesta-age was developed and the 9th percentile for gesta-tional age was used. tional age was used.

The ideal time to look for nuchal translucency is The ideal time to look for nuchal translucency is between 10-14 weeks’ gestation. Why? This is the between 10-14 weeks’ gestation. Why? This is the time when the fetal lymphatic system is developing time when the fetal lymphatic system is developing and the peripheral resistance of the placenta is high. and the peripheral resistance of the placenta is high. After 14 weeks the lymphatic system is developed After 14 weeks the lymphatic system is developed enough to drain any accumulating fluid and the enough to drain any accumulating fluid and the placental peripheral resistance is dropping. placental peripheral resistance is dropping.

CVS should be offered. CVS should be offered.

NT NT

Diagnostic value Diagnostic value There is a 10% risk of major abnormality when the There is a 10% risk of major abnormality when the

measurement is >3 mm, increasing to 90% at >6 measurement is >3 mm, increasing to 90% at >6 The abnormalities are mainly chromosomal. Abnormal The abnormalities are mainly chromosomal. Abnormal

NT of NT of 2.5 mm include 77% of babies with Down 2.5 mm include 77% of babies with Down syndrome and a similar percent of babies with syndrome and a similar percent of babies with other chromosomal abnormalities. other chromosomal abnormalities.

A normal measurement does not guarantee normality. A normal measurement does not guarantee normality. Trisomy 21: Chromosome 21 carries the gene that Trisomy 21: Chromosome 21 carries the gene that is codes for type VI collagen. Trisomy 21 is codes for type VI collagen. Trisomy 21 over- over-expression of one subunit of this collagen expression of one subunit of this collagen CT CT that has more elastic composition. that has more elastic composition. Neuromuscular abnormalities Neuromuscular abnormalities poor breathing poor breathing and body movements and body movements oedema. oedema. Intra- and extra-thoracic compressive syndromes Intra- and extra-thoracic compressive syndromes congestion of the vessels in the fetus’s head and congestion of the vessels in the fetus’s head and neck. neck. Heart failure, due to congenital cardiac abnormal-Heart failure, due to congenital cardiac abnormal-ity or cardiac dysfunction. ity or cardiac dysfunction.

Prerequisites Prerequisites

- The measurement is done at 10-14 w. - The measurement is done at 10-14 w.

- Sagittal view of the fetus. - Sagittal view of the fetus.

- Neutral position between head flexion - Neutral position between head flexion and extension. and extension.

- The maximum transluscent distance is - The maximum transluscent distance is measured. measured.

- The amnion should be identified - The amnion should be identified separately from the skin. separately from the skin.

The detailed anomaly scanThe detailed anomaly scan

This is normally undertaken between 18 and 20 weeks' gestation.

The head:The head: The following structures are to The following structures are to be examined: the skull bones for their be examined: the skull bones for their

integrity, the brain, the orbit and the lips. integrity, the brain, the orbit and the lips. Facial profile and the ears are examined Facial profile and the ears are examined

too. too.

The brain: Within each cerebral hemisphere is the lateral vent-ricle which contains the choroid plexus (a vascular echogenic structure which produces most of the CSF). The third ventricle is a central structure narrowed by the development of the thalamus on either side. The 4th ventricle lies in the hindbrain which lies anterior to the cerebellum.

Then the transcerebellar plane Then the transcerebellar plane should be obtained. Originating should be obtained. Originating

from the transthalamic plane the from the transthalamic plane the transducer is rotated until the transducer is rotated until the

cerebellar hemispheres (double cerebellar hemispheres (double head dumb-bell like structures) are head dumb-bell like structures) are

viewed. viewed.

Abnormal transcerebellar view Abnormal transcerebellar view

A cerebellum which is banana shaped is associated with spina bifida. The transcerebellar distance (TCD) is measured from the outer edge of one hemisphere to the outer edge of the other. Hypoplasia (small TCD) may be associated with spina bifida. The cisterna magna (a space posterior to the cerebellum) is usually not greater than 10 mm. It is usually very enlarged with the Dandy-Walker malformation which is associated with cerebellar hypoplasia.

The transventricular plane The transventricular plane

It is used to assess the lateral vent-It is used to assess the lateral vent-ricles to determine if there is ventriculo ricles to determine if there is ventriculo megally or choroid plexus cysts. megally or choroid plexus cysts. Originating from the transthalamic Originating from the transthalamic plane the transducer is rotated until the plane the transducer is rotated until the choroid plexus is identified. This arises choroid plexus is identified. This arises from the medial wall of the vent-ricle from the medial wall of the vent-ricle and extends into the poster horn. and extends into the poster horn.

Choroid plexus cysts may be uni- or Choroid plexus cysts may be uni- or bilateral. bilateral.

Early cases of ventriculomegally may be Early cases of ventriculomegally may be identified by a >3 mm separation of identified by a >3 mm separation of the choroid plexus from the ventricular the choroid plexus from the ventricular wall. In late cases, the choroid plexus wall. In late cases, the choroid plexus will appear like the clapper of a bell will appear like the clapper of a bell (gravity dependent). (gravity dependent).

Early ventriculomegally

Choroid plexus cyst Choroid plexus cyst

Face Face

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