Ultrasound estimation of gestational age.

Many ultrasonologists feel that if they are unable to obtain a BPD measurement at the time of an ultrasound examination that they have somehow failed to do an adequate job. However, from the information outlined in this chapter, it can be seen that the biparietal diameter is only one measurement that can be taken of the fetus in order to estimate gestational age. Furthermore, since the recognition of variability in fetal head shape, absolute reliance on measurement of the fetal biparietal diameter for estimation of gestational age has become much less common, especially after 20 weeks of gestation. The move toward measurement of several parts of the fetal anatomy has been called fetal biometry. The purpose of this approach is to evaluate body proportion and symmetry of growth of different organ systems, in the hope of elucidating subtle patterns which might be recognized as abnormal in very early stages when some form of prenatal management might improve reproductive outcome. Simultaneously, with the implementation of this approach to estimating age, a desire to inject an element of "quality control" into the obstetric ultrasound examination has come about. It has been found that measurement of more than one fetal parameter, in a sense, prevents overreliance on any single measurement, which, by itself, might mislead the clinician. While an error of clinically significant magnitude can be made in any measurement, it is unlikely that an error of the same magnitude, in "the same direction" of over or underestimation of the actual, would occur. Thus, there is an element of protection of the patient built into this approach which makes it appealing intuitively. However, it is uncertain that measurement of BPD, head circumference, abdominal circumference, and femur length will, in all cases, give a better estimate of gestational age than will measurement of the BPD alone. Recent data from Hadlock et al. showed that in 177 normal pregnancies, there was significant improvement in the ultrasound estimation of estimated date of delivery when two or more parameters were used to make that estimate rather than just BPD alone. Prior to 36 weeks, the optimal combination of parameters included the biparietal diameter, the abdominal circumference, and the femur length. However, after 36 weeks, the head circumference, abdominal circumference, and femur length gave the best estimate, with significant reduction in the mean errors, standard deviations, and size of maximum errors. Thus, it appears that the estimate using MFGP is both more accurate and precise than a single measurement.(ABSTRACT TRUNCATED AT 400 WORDS)

Human fetal breathing movements after carbohydrate ingestion in fasting and nonfasting subjects.

Human fetal breathing movements were observed by means of the linear array real-time B-scan technique in 40 study sessions at 35 to 36 week's gestation. Fasting and nonfasting subjects received water or 75 gm of glucose orally. Fetal breathing activity, observed as movement of the chest wall, was analyzed. The data support conclusions that fetal breathing increased after maternal ingestion of glucose in both fasting and nonfasting subjects, that the absolute increases in fetal breathing were similar for fasting and nonfasting subjects, and that fetal breathing occurred more frequently in nonfasting control subjects than in fasting control subjects in the setting of the study.

Comparison of ultrasound femur length and biparietal diameter in late pregnancy.

A linear relationship between growth of fetal femur length (FL) and biparietal diameter (BPD) after 22 weeks' gestation is described. The normal ratio of femur length to BPD (FL/BPD ratio) was found to be 79 +/- 8%. Effective uses of the FL/BPD ratio include its use as a quality control check on femur length and BPD measurements and its use to diagnose short-limbed dwarfism, hydrocephalus, and microcephaly. Pregnancy dating by means of BPD can now be cross checked by use of femur measurements and new observations on normal and abnormal fetal growth will now be possible.

Ultrasound placental site in relation to bloody taps in midtrimester amniocentesis.

In an unselected, consecutive series of 137 midtrimester amniocenteses for prenatal genetic diagnosis, it was found that the incidence of blood contamination of amniotic fluid samples was similar regardless of placental site as determined by ultrasound localization. Three (5.8%) patients with anterior placental location versus 5 (9.1%) patients with posterior placentas had gross blood in the amniotic fluid by visual inspection. These results support the view that placental penetration during amniocentesis is not the major cause of bloody taps. Ultrasound studies done prior to midtrimester amniocentesis should, perhaps, be more specifically evaluated in relation to pregnancy information obtained rather than solely as an aid to improve technical performance of amniocentesis.

Private practice use of real-time B scan ultrasound in obstetrics and gynecology.

An informal survey of 25 obstetrics and gynecology practices that use real time B scan ultrasound equipment was carried out to assess the economic and patient-care impact of such equipment. From this informal survey, it can be seen that the incorporation of real time B scan ultrasound scanning into private practice has become economically feasible and useful for the daily clinical management of obstetric patients. The implications and economics of such changes for obstetric health care costs remain to be assessed.

Fetal evaluation by real-time imaging.

The application of real-time imaging to the study of fetal morphology and function is an exciting advance. Rapid accurate study of fetal dynamics is possible with this apparently safe, noninvasive technique. Animal studies have revealed the general physiology of fetal breathing movements, which are now under extensive investigation with real-time imaging in the human. There is evidence for circadian rhythm of human fetal breathing movements as well as a relationship to maternal substrate loading. The presence of fetal breathing movements of the rapid irregular type may be a reassuring sign in the presence of other indicators of fetal compromise. Using real-time B-scan imaging, we have found long periods of apnea in pregnancies with normal perinatal outcome. As suggested in the animal studies, changes in fetal breathing patterns prior to fetal death may be more complex than originally thought. The techique of real-time B-scan imaging with precise definition of apnea, general movements, and fetal breathing will provide valuable information on which to base our evaluation of the clinical usefulness of fetal breathing movement studies in the management of pregnancy.

Screening for intrauterine growth retardation using the ultrasound biparietal diameter.

Fifteen hundred patients were scanned to predict fetal age and weight by biparietal diameter measurement. three hundred eleven patients had more than one scan. Forty-three small for gestational age (SGA) babies were ultimately delivered in this population. Prenatal ultrasound screening criteria for grouping into appropriate for gestational age (AGA) or small for gestational age (SGA) categories were: a) only an absolute biparietal diameter below the third percentile for the reference Rochester region population; b) only delta BPD calculated as less than 50 percent of the mean growth rate for the reference population; and c) a combination of these two factors. Intrauterine growth retardation was most accurately determined when an absolutely small biparietal diameter was found (at the time of the last ultrasound examination) in a woman with accurate gestational age assessment. Least accurate was the prediction based on one biparietal diameter measurement in a woman with poor clinical dates. A 50 percent false positive detection rate and poor sensitivity to intrauterine growth retardation were found using ultrasound biparietal diameter measurements as a screening test in this manner.