Assessment of Gestational Age by Ultrasound

Fetal biometric data are available for twin gestations 81 , 82 , 83 , 84 , 85 ; however, triplet and quadruplet pregnancies have not been adequately studied owing to their infrequent occurrence. In general, ultrasound-derived fetal dating tables obtained for singleton pregnancies can be used accurately for twin pregnancies until approximately 30 weeks' gestation. Grumbach and co-workers 86 have suggested that the femur continues to grow normally throughout pregnancy in twin gestations, while the head BPD and HC and abdominal AC growth rates decrease in the last 10 weeks of pregnancy.

Although further studies are required to confirm these findings, this study suggests that FL measurement may be a more reliable parameter to use for gestational age assessment in twin gestations during the third trimester. Gestational age estimations in twin pregnancies prior to 30 weeks' gestation should be performed in a similar manner to that for singleton pregnancies.

A simple, but uniform approach to the evaluation of gestational age should be performed in all fetuses.

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The ultrasound assessment of fetal age is based on the earliest ultrasound study, provided the measurement is technically adequate. Early in gestation fetal measurements have the least variability and, therefore, are most likely to predict fetal age. In the first trimester, the CRL measurement is used to estimate gestational age, whereas in the second and third trimesters fetal head BPD and HC , body AC , and extremity FL measurements are used to assess gestational age.

The following guidelines are recommended for the assessment of gestational age:. Use of the multiple parameters method of assessing gestational age is valid when the gestational age estimates of the various ultrasound parameters are similar. If the gestational age estimates of one or several parameters is greater than 2 weeks different than the estimates of the other parameters, either the abnormal ultrasound parameters should be excluded or a different method should be used to estimate gestational age.

When the various ultrasound parameters predict different gestational ages the fetus should be further evaluated to explain these differences. For example, an abnormally small FL measurement may suggest short-limb defects, a large BPD may be secondary to hydrocephalus, and an abnormally small or large AC measurement may suggest asymmetric intrauterine growth retardation or macrosomia, respectively.

In the instance of an abnormal cephalic index, the HC should be used to estimate gestational age, rather than the BPD measurement. In conclusion, assessment of gestational age is fundamental to obstetric care and should be a carefully thought-out process. Assessment should depend on history and physical examination, as well as ultrasound evaluation.


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Liquor amnii in the management of the pregnancy complicated by rhesus sensitization. Goldenberg RL, Nelson K: Iatrogenic respiratory distress syndrome. Neonatal respiratory distress following elective delivery: Routine ultrasound screening for the prediction of gestational age. Assessment of fetal maturity and dysmaturity. Ultrasound in managing the high-risk pregnancy. In Spellacy WD ed: Management of the High-Risk Pregnancy, pp — Baltimore, University Park Press, Clinical estimation of gestational age: Rules for avoiding preterm delivery.

Why is a fetal growth scan needed?

Ultrasound scanning of ovaries to detect ovulation in women. Variability of ovarian follicular growth in natural menstrual cycles.

Gestational Age Determination by Ultrasound

Growth and development of the human fetus prior to the twentieth week of gestation. Length and depth of the uterus and the diameter of the gestation sac in normal gravidas during early pregnancy. Acta Obstet Gynecol Scand 50 suppl: Br J Obstet Gynaecol The ultrasonic measurement of fetal crown-rump length as a method of assessing gestational age. Underestimation of gestational age by conventional crown-rump length growth curves.

The prediction of fetal maturity by ultrasonic measurement of the biparietal diameter. J Obstet Gynaecol Br Commonw Sonar BPD and fetal age: Definition of the relationship. Campbell S, Newman GB: Growth of the fetal biparietal diameter during normal pregnancy. Sabbagha RE, Hughey M: Standardization of sonar cephalometry and gestational age.

Analysis of percentile growth differences in two normal populations using same methodology. Hughey M, Sabbagha RE: Cephalometry by real time imaging: Am J Obstct Gynecol Analysis of biparietal diameter as an accurate indicator of gestational age. J Clin Ultrasound 8: A critical reevaluation of the relation to menstrual age by means of realtime ultrasound.

J Ultrasound Med 1: Improved prediction of gestational age from fetal head measurement. Relation to menstrual age. Campbell S, Wilken D: Ultrasonic measurement of fetal abdomen circumference in the estimation of fetal weight. Percentile ranks of sonar fetal abdominal circumference measurements. Fetal abdominal circumference as a predictor of menstrual age. A date-independent predictor of intrauterine growth retardation: Normal growth of the fetal biparietal diameter and the abdominal diameter in a longitudinal study.

Acta Obstet Gynecol Scand Ultrasound measurement of fetal limb bones. Assessment of gestational age in the second trimester by real-time ultrasound measurement of the femur length. Fetal femur length as a predictor of menstrual age. Estimation of gestational age from measurement of fetal long bones. J Ultrasound Med 3: Ultrasonic evaluation of fetal ventricular growth. A new parameter for prenatal diagnosis and dating. A new way to estimate fetal age. Cerebellar measurements with ultrasonography in the evaluation of fetal growth and development. Prenatal sonographic assessment of the fetal thorax: A new biometric parameter for estimation of gestational age.

Sonographic appearance of the fetal heel ossification centers and foot length measurements provide independent markers for gestational age estimation. Sonar measurement of fetal crown-rump length as means of assessing maturity of first trimester of pregnancy. Br Med J 4: The prediction of delivery date by ultrasonic measurement of fetal crown-rump length. Relation of birth weight, gestational age, and the rate of intrauterine growth to perinatal mortality. Clin Obstet Gynecol Comparative analysis of ultrasonographic methods of gestational age assessment.

J Ultrasound Med 2: A comparison of the reliability of the estimated date of confinement predicted by crown-rump length and biparietal diameter. Intrauterine growth as estimated from live-born weight data at 24—42 weeks of gestation. A standard of fetal growth for the United States of America. Fetal growth and perinatal viability in California. Mantoni M, Pedersen JF: Fetal growth delay in threatened abortion: Shepard M, Filly RA: A standardized plane for biparietal diameter measurement.

Rational choice of plane of section for sonographic measurement. A comparison of real time and conventional B-scan techniques.

J Clin Ultrasound 4: Lunt RM, Chard L: Reproducibility of measurement of fetal biparietal diameter by ultrasonic cephalometry. The limitations of ultrasonic fetal cephalometry. An evaluation of two methods for measuring fetal head and body circumferences. Effect of head shape on BPD. Fetal head and abdominal circumferences: Ellipse calculations versus planimetry.


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J Clin Ultrasound Campbell S, Thorns A: Ultrasound measurement of the fetal head to abdomen circumference ratio in the assessment of growth retardation. Pitfalls in femur length measurements. J Ultrasound Med 6: Ultrasonographic identification of fetal lower extremity epiphyseal ossification centers. Comparison of biparietal diameter and femur length in the third trimester: Effects of gestational age and variation in fetal growth. J Ultrasound Med 5: Measurement accuracy of sonographic sector scanners.

Accuracy of ultrasound in fetal femur length determination: A comparison of sector and linear array scanners for the measurement of the fetal femur. J Ultrasound Med 4: Comparison of ultrasound femur length and biparietal diameter in late pregnancy. Abramowicz J, Jaffe R: Comparison between lateral and axial ultrasonic measurements of the fetal femur.

Fetal femur length, neonatal crown-heel length, and screening for intrauterine growth retardation. Three fetal ponderal indexes in normal pregnancy. Poor predictor of intrauterine growth retardation. Poor predictor of macrosomic fetuses in diabetic mothers. Growth adjustment sonographic age GASA: Computer-assisted analysis of multiple fetal growth parameters. Estimating fetal age using multiple parameters: A prospective evaluation in a racially mixed population. Sonal cephalometry in twins: A table of biparietal diameters for normal twin fetuses and a comparison with singletons.

Ultrasound growth patterns in normal and discordant twins. Sonar cephalometry in twin pregnancy: Discordancy of the biparietal diameter after 28 weeks' gestation. Diminished biparietal diameter and abdominal circumference growth in normal twins. Twin and singleton growth patterns compared using ultrasound. We use cookies to ensure you get the best experience from our website. By using the website or clicking OK we will assume you are happy to receive all cookies from us. More info on cookies. This chapter should be cited as follows: Due to the variation of ultrasound measurements, a minimum of two weeks is required between fetal growth scans.

Other signs that may indicate FGR are changes in the umbilical cord blood flow and reduced amniotic fluid volume. If fetal growth restriction is suspected your health carer may recommend some tests to identify the underlying cause. Tests that may be offered include:. If growth restriction is suspected, hospital admission may be required so that regular fetal surveillance can be undertaken. Fetal heart rate monitoring by cardiotocograph CTG may be performed. If the fetal condition is considered poor and continuation of the pregnancy is not considered safe, then delivery is considered.

If delivery is recommended before 37 weeks gestation, your maternity care provider will consider maternal steroid injections and magnesium sulphate if less than 30 weeks to reduce the risk to the newborn of complications associated with prematurity.

Fetus Measurement Growth Calculators

A newborn baby that has had trouble growing in the uterus may need to be cared for in the Neonatal Critical Care Unit depending on their prematurity, birth weight and how well they adapt to life outside the uterus. Most fetuses that are shown to be large for gestational age on ultrasound are well nourished and healthy at birth. In some cases there is an underlying cause for the fetus to be large such as diabetes or a genetic syndrome. Some babies are larger due to maternal diabetes during pregnancy and in particular if maternal blood glucose levels have been difficult to control.

Larger babies born to mothers with diabetes are at increased risk of birth trauma including shoulder dystocia. When the fetus is suspected to be excessively large, induction of labour or caesarean section may be considered.

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When the mother has diabetes in pregnancy, their babies are also at risk of low blood sugar hypoglycaemia after birth as they no longer have access to the high sugar levels that they have become used to while in the uterus. This may require monitoring and treatment in the special care nursery. Quick Links Why is a fetal growth scan needed? What happens during a fetal growth scan? Why is a fetal growth scan needed?

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Common reasons to have a fetal growth scan in pregnancy include the following: Your abdomen measures smaller or larger than expected. Maternal diabetes or high blood pressure. The main fetal measurements taken for a growth scan include: An ultrasound scan to look for major fetal abnormalities is routinely performed earlier in pregnancy between 18 and 20 weeks gestation see the brochure Ultrasound—your 18 to 20 week scan Small for gestational age SGA Most fetuses that are shown to be small for gestational age are healthy but some may require further ultrasound assessment to ensure that they are growing adequately.

What is fetal growth restriction FGR? What causes fetal growth restriction? Some of the underlying causes of FGR include the following: Placental insufficiency—when the placenta fails to provide adequate nutrition to the developing fetus. Fetal abnormality—some fetal abnormalities are associated with delayed growth. Multiple pregnancy—can affect one or more of the fetuses.

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