Evaluation of Gestation



Prenatal assessment of gestational age and estimated date of delivery

Gestational age, synonymous with menstrual age, is defined in weeks beginning from the first day gestaational the last menstrual period LMP prior to ultrasonud. Accurate determination of gestational age is fundamental to obstetric care and is important in a variety of situations. For example, antenatal test interpretation may be dependent on gestational age. Again, inaccurate assessment of gestational age will lead to errors in assessing the severity of fetal gestational age dating ultrasound by the delta OD Fetal growth assessment, either clinically or by ultrasound evaluation, also relies on accurate assessment of gestational age.

Fetal growth gestational age dating ultrasound or macrosomia may be missed or incorrectly diagnosed owing to errors in gestational age assignment. Interpretation of antenatal biophysical testing non-stress tests gestational age dating ultrasound biophysical profiles may be subject ultdasound variation with gestational age as well. Gestational age dating ultrasound heart rate reactivity and fetal breathing develop with advancing gestational age; therefore, the absence of these biophysical parameters may be interpreted as abnormal for fetuses in whom the gestational age has been overestimated.

Obstetric management is also dependent on gestational gestational age dating ultrasound. Proper decisions regarding presumed preterm labor or postdate pregnancies are only possible when gestational age is accurately estimated. Likewise, timing of repeat cesarean section requires accurate assessment of dates. In the past gestational age was established by a combination of the historical information and the physical examination. Other factors include assessment of uterine size by bimanual examination in the first trimester, initial detection of gestational age dating ultrasound heart tones by Doppler 10—12 weeks or auscultation 19—21 gestational age dating ultrasoundand uterine fundal height measurement.

However, both the history and the findings on physical examination are fraught with error, even in the best of circumstances Table 1. Clearly, the inaccuracies of history and physical examination may limit their usefulness in assessment of gestational age. Methods that assess the time of ovulation or conception can accurately establish gestational age. Ovulation induction with agents such as clomiphene citrate and Pergonal, also accurately predicts gestational age.

However, in most pregnancies, the date of ovulation or conception cannot be as accurately predicted as outlined above and gestational age must be established by other methods. The advent of ultrasound has allowed a more direct means utrasound assessing fetal structures and development. Measurements of a wide variety of parameters have been devised to establish gestational age.

Ultrasound assessment of gestational age is feasible in a majority of pregnancies and may be used to establish geestational age with greater accuracy than physical examination. In the first trimester, gestational sac mean diameter and crown-rump length measurements have become the primary means of evaluating gestational age. Those parameters most commonly measured include biparietal diameter, 202122232425262728 head circumference, 2930 abdominal circumference, 3132333435 and femur length.

First-Trimester Gestational age dating ultrasound In the first trimester, the gestational sac mean diameter and crown-rump length are used to establish fetal age. Both parameters are useful because each measures a different gestationaal of the first-trimester pregnancy and may be used at different times during the first trimester. The gestational sac is the first identifiable structure routinely imaged in the first trimester.

It is identified by transabdominal ultrasound as early as 5 weeks' gestation and may be seen as early as 4 weeks' gestation by transvaginal ultrasound. The sac is lutrasound inside the gestational age dating ultrasound rim, including only the echo-free space Fig. The gestational sac is imaged first in the longitudinal plane, obtaining long axis and anteroposterior ultrasouhd perpendicular to each other.

Then, in the transverse plane at the level of the anteroposterior measurement, the width measurement gestational age dating ultrasound obtained. The three measurements are averaged to obtain the gestational sac mean diameter. Table 2 compares gestational ages from 5 to 12 weeks gestational age dating ultrasound the gestational sac mean diameters.

Gestational Sac Mean Diameter Measurements Relative to Gestational Age. Longitudinal image of a gestational gestational age dating ultrasound. The longitudinal diameter is measured between the small crosses 1 and the anteroposterior diameter is measured between the larger crosses 2. Transverse image obtained at the level of the anteroposterior diameter. The transverse diameter is measured between the crosses. The crown-rump length CRL is a measurement of the embryo, usually identified at 6 to 7 weeks' gestation.

Crown-rump length may be used to accurately date pregnancy between 7 and 13 weeks' gestation. The technique involves measurement of the fetal length from the tip of the cephalic pole to the tip of the caudal pole. The fetus should be at rest and assuming its natural curvature. At 5 to 6 weeks' gestation, distinct landmarks cannot always be identified but heart motion usually can be detected centrally.

As the pregnancy continues, the head can be easily identified from the rest of the body. After 12 weeks' gestation excessive curvature of the fetus may lead to erroneous shortening of CRL measurement; therefore, other measurements, such as the biparietal diameter, should be used to estimate gestational age. Ultrasound image of a fetus at 10 weeks' gestation.

The crown-rump length is measured along the longest axis of the fetus between the arrows. The wavelength dating reviews between sonographic CRL values and dates was first reported by Robinson and Fleming, who obtained CRLs in pregnancies of women with certain menstrual histories. Table 3 summarizes the results of these three studies evaluating gestational age relative to CRL. Crown-Rump Length Gesattional Relative to Gestational Age in Three Studies.

Variations in the measurement of CRL can be attributed to differences in fetal growth patterns. Such differences are related to factors similar to those that influence birth weight curves, including maternal age and parity, prepregnancy maternal weight, geographic location, and population characteristics.


Fetal age Vs Gestational age - Difference Between fetal age And gestational age