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Biometrie foetale: Revue et application de la determination du sexe

par Levi, Salvator ;Keuwez, José
Référence Ultrasound in medicine & biology, 10, 1, page (51-59)
Publication Publié, 1984

Article révisé par les pairs

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Résumé :

Diagnostic ultrasound was introduced in the practice of obstetrics through its ability to measure accurately the biparietal (DBP) diameter of the foetus. The development of bidimensional and grey tone images expanded the possibility of fetal biometry. One of its most important uses is the estimation of gestational age. A knowledge of foetal age is necessary to interpret the results of most of the investigations currently performed during pregnancy. Different fetal dimensions increase with age at different rates according to the period of gestation. During the embryonic period, the crown-rump length gives a very good estimation of age within 4-6 days for twice the standard deviation. Later on, because of the curvature of the fetus, the age is estimated with the DBP. The accuracy diminishes with the slowing down of fetal growth, from 12 weeks onwards, when twice the standard deviation of the age estimate may be as long as 2 weeks. When DBP is no longer reliable in determining age, femur length is measured being more reliable for that purpose at least till 24 weeks. A very early assessment of foetal age reduces the risk of errors in estimating the duration of pregnancy and is important to detect early growth retardation (IUGR); this is usually symmetric, i.e. affecting all fetal parts (versus asymmetrical or late IUGR where trunk growth is first involved). Fetal weight can be estimated by fetal parts measurements. A formula was derived as long as twenty years ago but not all authorities agree on any measuring technique as evidenced by the many different formulas proposed-a sign that no very satisfactory one yet exists. Nevertheless the estimate should not exceed 15% of the true weight. The calculation of the fetal volume should theoretically be the best method but it needs sophisticated computer and software facilities. Besides head, trunk and limbs, any other fetal structures may be measured such as adrenals, kidneys, cerebral ventricles, orbits. They contribute more particularly to the detection of fetal abnormalities. Detection of retarded fetal growth (IUGR) is one of the major goals of pregnancy surveillance by ultrasound. The authors report on a prospective study based on 2 ultrasound examinations only, the first to assess gestational age, the second fetal growth. The head, chest and abdominal diameters which were below the 20 percentile indicated the cases at risk. Later on, the precocity and accuracy of our antenatal ultrasound determination of fetal sex was an incitement to collect separate biometrial data for male and female fetuses. Their differences were statistically significant and applied therefore to a new appraisal of (IUGR) detection. The new norms brought a higher sensitivity, lower specificity and also a higher predictivity but for DBP only. © 1984.