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Atlas of Human Body Ultrasound Scanning_ Methods and Diagnostic Applications ( PDFDrive ).pdf
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13  Normal Pregnancy

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1.10\ Nuchal Translucency (NT)

Fig. 13.10  NT is measured in this middle sagittal section. 1D:NT is 0.11 cm (i.e., 1.1 mm)

NT

NT

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1.10.1\ Scanning Method

The same image section as CRL measured is shown. The image should be magnified, to let the fetal area occupying 2/3 of the screen.

1.10.2\ Section Structures

Fetal head and thorax are shown in this median sagittal section, with nasal bone recognized. Long axis view of nuchal translucency should be shown clearly in this section, which is the hyaline layer under the back neck skin.

1.10.3\ Measuring Method

The thickest diameter of nuchal translucency is measured. Please note the following comments when NT is measured: (1) CRL value should be between 45 and 84 mm, while gestational age is between 11 and 13 weeks and 6 days. (2) The image is acquired in the fetal median sagittal section. (3) Fetal neck is located in the middle of the image. (4) Fetal image should be magnified, to let the fetal area occupying 75% of the screen. (5) The amnion should be distinguished from the fetal skin.

(6) The measuring calipers should be placed on the inner border of the bilateral echoic lines of the hyaline region. (7) Measure three times, and the largest value is recorded finally for risk calculating.

1.10.4\ Clinical Significance

NT is mainly used for risk calculating of fetal chromosomal abnormalities, because 90% of chromosomal abnormal fetuses could be found out when NT is used in combination with maternal serum pregnancy-associated plasma protein A (PAPP-A) and free human chorionic gonadotropin in beta subunit (β-hCG). Furthermore, thickened NT is also related to early fetal heart failure, lymphatic retardation, and elevated fetal thorax pressure. It is considered that the fetus is in a high risk of chromosomal abnormality when NT is or larger than 2.5 mm. But NT increases nonlinearly with the growth of pregnancy, so a cutoff value of NT is not recommended to be simply used in clinic consultation, and NT should be considered in combination with CRL, maternal age, etc.

1.10.5\ Normal Reference Values

Thickness of NT increases with the growth of pregnancy between 11 weeks and 13 weeks and 6 days. It is reported that the median of NT is 1.5 mm and the 95th% of NT is 2.4 mm in normal chromosome and low-risk populations, while the median of NT is 1.5 mm, and the 95th% of NT is 2.5 mm in abnormal chromosome and high-risk populations.

13  Normal Pregnancy

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2\ Second Trimester and Third

Trimester Scanning

Second trimester is referred to pregnancies between 13 weeks and 27.6 weeks of gestation, and third trimester is referred to pregnancies between 28 and 40 weeks of gestation. It is called full-­term pregnancy when the pregnancy is more

than 37 weeks. Recently, in terms of the Fetal Medicine Foundation (FMF), pregnancies less than 14 weeks are included in first trimester.

The fetus grows, develops, and grows up during the second and third trimester, and similar ultrasound images are shown during the second or third trimester.

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3\ Judgment of Fetal Lie

and Fetal Position

3.1\ Judgment of the Fetal Lie

and Presentation

3.1.1\ Cephalic Presentation of Fetus

Fig. 13.11  The fetus is in cephalic presentation of longitudinal lie. AF amniotic fluid, LEG leg, FB fetal body, FH fetal head

AF

FB

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FH

LEG