Percentile ranks of sonar fetal abdominal circumference measurements

Influence of maternal body mass index on interobserver variability of fetal ultrasound biometry and amniotic-fluid assessment in late pregnancy

OBJECTIVE

To determine the interobserver reproducibility of fetal ultrasound biometric and amniotic-fluid measurements in the third trimester of pregnancy, according to maternal body mass index (BMI) category.

METHODS

This was a prospective cohort study of women with a singleton gestation beyond 34 weeks, recruited into four groups according to BMI category: normal (18.0-24.9 kg/m² ), overweight (25.0-29.9 kg/m²⁾ , obese (30.0-39.9 kg/m² ) and morbidly obese (≥ 40 kg/m² ). Multiple pregnancies, women with diabetes and pregnancies with a fetal growth, structural or genetic abnormality were excluded. In each woman, fetal biometric (biparietal diameter (BPD), head circumference, abdominal circumference (AC), femur length (FL) and estimated fetal weight) and amniotic-fluid (amniotic-fluid index (AFI) and maximum vertical pocket (MVP)) measurements were obtained by two experienced sonographers or physicians, blinded to gestational age and each other's measurements. Differences in measurements between observers were expressed as gestational age-specific Z-scores. The interobserver intraclass correlation coefficient (ICC) and Cronbach's reliability coefficient (CRC) were calculated. Bland-Altman analysis was used to assess the degree of reproducibility.

RESULTS

In total, 110 women were enrolled prospectively (including 1320 measurements obtained by 17 sonographers or physicians). Twenty (18.2%) women had normal BMI, 30 (27.3%) women were overweight, 30 (27.3%) women were obese and 30 (27.3%) women were morbidly obese. Except for AFI (ICC, 0.65; CRC, 0.78) and MVP (ICC, 0.49; CRC, 0.66), all parameters had a very high level of interobserver reproducibility (ICC, 0.72-0.87; CRC, 0.84-0.93). When assessing reproducibility according to BMI category, BPD measurements had a very high level of reproducibility (ICC ≥ 0.85; CRC > 0.90) in all groups. The reproducibility of AC and FL measurements increased with increasing BMI, while the reproducibility of MVP measurements decreased. Among the biometric parameters, the difference between the BMI categories in measurement-difference Z-score was significant only for FL. Interobserver differences for biometric measurements fell within the 95% limits of agreement.

CONCLUSION

Obesity does not seem to impact negatively on the reproducibility of ultrasound measurements of fetal biometric parameters when undertaken by experienced sonographers or physicians who commonly assess overweight, obese and morbidly obese women. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Systematic review of methodology used in ultrasound studies aimed at creating charts of fetal size

BACKGROUND

Reliable ultrasound charts are necessary for the prenatal assessment of fetal size, yet there is a wide variation of methodologies for the creation of such charts.

OBJECTIVE

To evaluate the methodological quality of studies of fetal biometry using a set of predefined quality criteria of study design, statistical analysis and reporting methods.

SEARCH STRATEGY

Electronic searches in MEDLINE, EMBASE and CINAHL, and references of retrieved articles.

SELECTION CRITERIA

Observational studies whose primary aim was to create ultrasound size charts for bi-parietal diameter, head circumference, abdominal circumference and femur length in fetuses from singleton pregnancies.

DATA COLLECTION AND ANALYSIS

Studies were scored against a predefined set of independently agreed methodological criteria and an overall quality score was given to each study. Multiple regression analysis between quality scores and study characteristics was performed.

MAIN RESULTS

Eighty-three studies met the inclusion criteria. The highest potential for bias was noted in the following fields: 'Inclusion/exclusion criteria', as none of the studies defined a rigorous set of antenatal or fetal conditions which should be excluded from analysis; 'Ultrasound quality control measures', as no study demonstrated a comprehensive quality assurance strategy; and 'Sample size calculation', which was apparent in six studies only. On multiple regression analysis, there was a positive correlation between quality scores and year of publication: quality has improved with time, yet considerable heterogeneity in study methodology is still observed today.

CONCLUSIONS

There is considerable methodological heterogeneity in studies of fetal biometry. Standardisation of methodologies is necessary in order to make correct interpretations and comparisons between different charts. A checklist of recommended methodologies is proposed.

Intra- and interobserver variability in fetal ultrasound measurements

OBJECTIVE

To assess intra- and interobserver variability of fetal biometry measurements throughout pregnancy.

METHODS

A total of 175 scans (of 140 fetuses) were prospectively performed at 14-41 weeks of gestation ensuring an even distribution throughout gestation. From among three experienced sonographers, a pair of observers independently acquired a duplicate set of seven standard measurements for each fetus. Differences between and within observers were expressed in measurement units (mm), as a percentage of fetal dimensions and as gestational age-specific Z-scores. For all comparisons, Bland-Altman plots were used to quantify limits of agreement.

RESULTS

When using measurement units (mm) to express differences, both intra- and interobserver variability increased with gestational age. However, when measurement of variability took into account the increasing fetal size and was expressed as a percentage or Z-score, it remained constant throughout gestation. When expressed as a percentage or Z-score, the 95% limits of agreement for intraobserver difference for head circumference (HC) were ± 3.0% or 0.67; they were ± 5.3% or 0.90 and ± 6.6% or 0.94 for abdominal circumference (AC) and femur length (FL), respectively. The corresponding values for interobserver differences were ± 4.9% or 0.99 for HC, ± 8.8% or 1.35 for AC and ± 11.1% or 1.43 for FL.

CONCLUSIONS

Although intra- and interobserver variability increases with advancing gestation when expressed in millimeters, both are constant as a percentage of the fetal dimensions or when reported as a Z-score. Thus, measurement variability should be considered when interpreting fetal growth rates.

Pathophysiology of Fetal Growth Restriction: Implications for Diagnosis and Surveillance

Normal fetal growth depends on the genetically predetermined growth potential and is modulated by fetal, placental, maternal, and external factors. Fetuses with intrauterine growth restriction (IUGR) are at high risk for poor short- and long-term outcome. Although there are many underlying etiologies, IUGR resulting from placental insufficiency is most relevant clinically because outcome could be altered by appropriate diagnosis and timely delivery. A diagnostic approach that aims to separate IUGR resulting from placental disease from constitutionally small fetuses and those with other underlying etiologies (e.g., aneuploidy, viral infection, nonaneuploid syndromes) needs to integrate multiple imaging modalities. In placental-based IUGR, cardiovascular and behavioral responses are interrelated with the disease severity. Ultrasound assessment of fetal anatomy, amniotic fluid volume, and growth is complementary to the Doppler investigation of fetoplacental blood flow dynamics. A diagnostic approach to IUGR combining these modalities is presented in this review.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to describe the development of the placental interface, to outline the mechanisms of placental insufficiency, and to list the manifestations of placental insufficiency and the tests that can be used to diagnose fetal growth restriction.

References intervals for fetal biometrical parameters

OBJECTIVE

To establish normal reference intervals for biparietal diameter, head circumference, abdominal circumference, and length of femur, a cross-sectional study.

STUDY DESIGN

Five hundred singleton fetuses for each week at gestations between 23 and 41 weeks with a total of 9500 fetuses. Antenatal ultrasound measurements from all consecutive pregnant women referred to the ultrasound unit for scanning of fetal condition are prospectively entered in a data bank. For the purpose of this study, sonographic measurements were collected retrospectively and each fetus contributed just one value to the reference sample.

RESULTS

The mean curve of the four biometrical parameters varied with gestational age, with flattening of the curves at the end of gestation and increased width of normal ranges with increasing gestational age. Maximal weekly increases occurred at 24 weeks' gestation for head circumference, abdominal circumference, and length of femur and at 26 weeks' gestation for biparietal diameter. The four biometrical parameters, however, showed 50% increases in size at 33 weeks' gestation.

CONCLUSIONS

These fetal size reference intervals are clinically relevant and can be used for populations with epidemiological features and distribution of neonatal birth weights similar to our data.

Fetal biometry: clinical, pathological, and technical considerations

Sonographic measurements of fetal ultrasound parameters are the basis for accurate determination of gestational age and detection of fetal growth abnormalities. Selection of the most useful single biometric parameter depends on the timing and purpose of measurement and is influenced by specific limitations. CRL (crown-rump length) is the best parameter for early dating of pregnancy. Biparietal diameter (BPD) maintains the closest correlation with gestational age in the second trimester. In cases of variation in the shape of the skull, head circumference is an effective alternative. Abdominal circumference is the most useful dimension to evaluate fetal growth, and femur length is the best parameter in the evaluation of skeletal dysplasia. Use of multiple predictors improves the accuracy of estimates. An individual approach to each pregnancy is recommended for fetal growth assessment. The various epidemiological factors involved in fetal growth should be considered and specific charts for different communities should be used when possible. The methods of fetal weight estimation with their limitations and potential errors are presented. Clinical application of fetal biometry in abnormal growth is discussed in cases of small- and large-for-gestational-age fetuses, chromosomal aberrations, and skeletal dysplasias.

Positive predictive value of suspected growth aberration in twin gestations

OBJECTIVE

Our purpose was to determine the positive predictive value of ultrasonographic surveillance for growth abnormalities in twin gestations as a function of gestational age.

STUDY DESIGN

Women with twin gestations and delivery between January 1992 and March 1998 who had a 20- to 24-week sonogram with normal fetal anatomic findings and who had at least 1 sonogram showing abnormal growth were identified. Abnormal growth on ultrasonography was defined as an estimated fetal weight <10th percentile, abdominal circumference <5th percentile, or twin discordance (>20% difference in twin weights as a function of the heavier twin). Birth weights were then assessed for evidence of twin discordance or growth restriction.

RESULTS

The positive predictive value for the occurrence of a growth abnormality at birth, after an abnormal growth finding on ultrasonography at any time during gestation, was 47.7%. The positive predictive value was greatest (85%) when suspected growth restriction was first documented at 20 to 24 weeks of gestation and decreased with increasing gestational age. Even though sonograms were obtained at a mean interval of 4.4 +/- 2.0 weeks, those gestations with normal growth at 20 to 24 weeks had an elapsed time of 10.3 +/- 3.9 weeks until a growth abnormality was subsequently detected.

CONCLUSION

In twin gestations the positive predictive value of a sonogram for a growth abnormality at birth is significantly decreased after normal findings on a 20- to 24-week sonogram. This finding suggests that a routine 2- to 4-week interval between sonograms for all twin gestations may be unwarranted.

Utilizing sonography to follow fetal growth

In utero diagnosis of fetal growth abnormalities continues to pose a clinical dilemma. Although significant advances have been made in the understanding of growth disturbances and their clinical importance, false-positive and false-negative diagnoses of IUGR and excessive fetal growth continue to affect the accuracy of antenatal diagnosis. Until more accurate methods are developed to aid in diagnosis, multiple biometric parameters should be assessed in patients either at risk for or with a suspected growth disturbance. Serial measurements obtained every 2 to 3 weeks may enhance diagnostic capabilities. Although antenatal diagnosis of IUGR has been shown to be of benefit in improving outcome, more study is needed to determine whether there is a benefit in antenatal diagnosis of macrosomia or LGA.

Molecular, radiologic, and histopathologic correlations in thanatophoric dysplasia

Various mutations in the fibroblast growth factor receptor 3 (FGFR3) gene have recently been reported in thanatophoric dysplasia (TD). We examined the clinical, radiographic, and histologic findings in 91 cases from the International Skeletal Dysplasia Registry and correlated them with the specific FGFR3 mutation. Every case of TD examined had an identifiable FGFR3 mutation. Radiographically, all of the cases with the Lys650Glu substitution demonstrated straight femora with craniosynostosis, and frequently a cloverleaf skull (CS) was demonstrated. In all other cases, the femora were curved, and CS was infrequently present but was occasionally as severe as TD with the Lys650Glu substitution. Histopathologically, all of the cases shared similar abnormalities, but cases with the Lys650Glu substitution had better preservation of the growth plate. Cases with the Tyr373Cys substitution tended to have more severe radiographic manifestations than the Arg248Cys cases, but there was overlap in the phenotypic spectrum between them. One common classification of TD distinguishes affected infants based on the presence or absence of CS. In contrast, and as originally proposed by Langer et al. [1987: Am J Med Genet 3: 167-179], our data suggest that TD can be divided into at least two groups (TD1 and TD2) based on the presence of straight or curved femora. The variable presence of CS and severity of the radiologic and histologic findings in the other substitutions may be due to other genetic, environmental, or stochastic factors.

The association of early-onset fetal growth restriction, elevated maternal serum alpha-fetoprotein, and the development of severe pre-eclampsia

From Antenatal Diagnostic Center referrals over 22 months, consultations for early-onset fetal growth restriction versus skeletal dysplasia were retrospectively identified. Those with elevated maternal serum alpha-fetoprotein (MSAFP) levels are the focus of this report. All had an early ultrasound confirming menstrual dates and subsequent sonography at < 28 weeks with at least two fetal biometric measures delayed by > or = 2 standard deviations from mean values. Of the five patients identified, the mean gestational age at the time of diagnosis of fetal growth restriction was 23.3 +/- 2.9 weeks. All had normal karyotypes and normal amniotic fluid AFP. None of the patients had evidence of hypertension or pre-eclampsia at diagnosis of fetal growth restriction. All five gravidas subsequently developed severe pre-eclampsia from 5.5 to 12.5 weeks after documentation of fetal growth delay. Three developed HELLP syndrome. Pregnancies were continued a mean duration of 10-2 weeks, with all five delivering at preterm gestations (mean = 33.5 +/- 1.7 weeks) for maternal indications of severe pre-eclampsia. Unexplained early-onset fetal growth restriction in conjunction with unexplained elevations of MSAFP together consistently heralded the subsequent development of severe pre-eclampsia.

Ultrasonographic assessment of fetal growth: comparison between human and ovine fetus

OBJECTIVE

Our purpose was to evaluate the rate of ovine fetal growth for several body parameters by serial ultrasonographic measurements and to compare them with analogous data in the human fetus.

STUDY DESIGN

Forty-three ewes with singleton gestations were studied. Four parameters were measured: biparietal diameter, abdominal circumference, femur length, and tibia length. Ultrasonographic examinations were performed weekly from 50 to 138 days of gestation (term 147 days). Quadratic regression analysis was used to describe each data set.

RESULTS

The biparietal diameter showed a significant deceleration of its growth rate. The abdominal circumference showed a linear growth pattern. Both femur and tibia revealed a significant acceleration of the growth rate.

CONCLUSION

The ovine fetal growth pattern is different from that observed in the human fetus, in which all four parameters show deceleration of the growth rate in late gestation. In comparison to the ovine, the human fetus reaches similar abdominal circumference and femur length values at term, but in a gestational period that is twice as long. In sharp contrast to abdominal circumference and femur length growth, the biparietal diameter has a similar growth rate in both species. Thus the human fetus has a slower rate of somatic growth and its greater biparietal diameter at term results from the longer gestational period.

Ultrasonographic growth measurements in triplet pregnancies

The incidence of triplet pregnancies is increasing due to the widespread use of ovulation induction agents and assisted conception treatments. The aim of this study was to acertain the normal ultrasonographic measurements for fetal growth parameters in triplet pregnancies. The ultrasonographic measurements of all triplet pregnancies managed in two major hospital centres were reviewed retrospectively and those in which there was less than 25% discordance in birth weight were included in the study. Triplet 50th centile for fetal biparietal diameter, whilst falling through the normal singleton centile range from 27 weeks gestation, did not fall below the 10th centile value of singletons. Triplet 50th centile for head circumference was equivalent to the singleton 10th centile from 23 weeks gestation. Triplet 50th centile for abdominal curcumference was persistently below that of the singleton 50th centile, falling below the singleton 10th centile from 29 weeks gestation. Normal growth rate of triplet gestations in the third trimester of pregnancy varies from that of singletons. An awareness of this altered growth rate is necessary to avoid the inappropriate diagnosis of asymmetrical triplet fetal growth retardation. We suggest that the growth curves presented here may be used to monitor triplet fetal growth.

Composite assessment of gestational age: a comparison of institutionally derived and published regression equations

OBJECTIVES

This study was undertaken to evaluate (1) the applicability of previously reported regression equations for gestational age assessment to our patient population in Pittsburgh and (2) whether the addition of radius length or its substitution for one of the other fetal measurements could improve the prediction of gestational age.

STUDY DESIGN

Five fetal parameters--biparietal diameter, head circumference, abdominal circumference, femur length, and radius length--were measured in a prospective cross-sectional study of gestational age assessment in 265 pregnant women between 13 and 43 weeks' gestation.

RESULTS

The regression equation derived for each fetal parameter was found to be quite similar to previously published reports. Although the coefficient of determination was only minimally affected, the variability improved with the institutionally derived regression equation.

CONCLUSION

The incorporation of several fetal measurements into a composite assessment of gestational age generally enhances the accuracy of the prediction. The addition of a second long bone to a gestational age assessment does not significantly improve results.

An infant with trisomy 9 mosaicism presenting as a complete trisomy 9 by amniocentesis

We present a case in which amniocentesis performed at 33 weeks' gestation because of symmetrical intrauterine growth retardation and decreased amniotic fluid volume led to the prenatal diagnosis of a fetus with a karyotype of 47,XX,+9,t(1;20)(q42;p11.2) pat, i.e., with an extra chromosome 9 and a balanced translocation between chromosomes 1 and 20. At delivery, the baby showed clinical features of trisomy 9, yet chromosome analysis of the cord blood revealed no trisomy 9 cells, a finding confirmed by neonatal blood karyotyping. The balanced translocation was present in all cells. A skin biopsy confirmed trisomy 9 mosaicism with 10 per cent trisomy 9 cells. The baby died at 6 weeks and an autopsy was obtained. Chromosome analysis of different organs demonstrated different frequencies of the mosaicism of trisomy 9. The possible underlying mechanism for the discrepancy between the karyotype results by amniocentesis and those of other tissues is discussed.

An elevated maternal serum alpha-fetoprotein leading to the diagnosis of an immature teratoma

A case report is presented of a woman with a maternal serum alpha-fetoprotein 17.46 multiples of the median (MOM), who was found to have an ovarian immature teratoma. It is suggested that patients who present with a maternal serum alpha-fetoprotein value greater than 9 multiples of the median receive a more comprehensive evaluation remembering that the alpha-fetoprotein in the adult can be a tumor marker.

A comparison of three methods of assessing inter-observer variation applied to ultrasonic fetal measurement in the third trimester

The inter-observer variation of fetal biparietal diameter, head circumference, abdominal circumference, and femoral length measured in the third trimester by ultrasound was studied by three different methods--coefficient of variation, correlation coefficient, and the 95% limits of agreement. The coefficients of variation were 1.6 to 3.7%, the correlation coefficients were 0.89 to 0.98 with P values of less than 0.001, yet the limits of agreement when applied to centile charts were found to be too wide to separate reliably small fetuses from those that were not small. We conclude that the limits of agreement is the preferred method of assessing inter-observer variation, and we suggest that future research into growth retardation move away from ultrasonic measurements of the fetus.

Estimation of birth weight by use of ultrasonographic formulas targeted to large-, appropriate-, and small-for-gestational-age fetuses

This report sought to determine whether estimates of fetal weight are enhanced by using ultrasonographic formulas targeted to the large-, appropriate-, and small-for-gestational-age fetus in both preterm and term pregnancies. Ultrasonographic fetal measurements from 575 singleton pregnancies were obtained within 7 days of delivery. The first 194 fetuses were classified into three groups on the basis of the growth percentile rank of the abdominal circumference (greater than or equal to 90%, greater than 5% and less than 90%, and less than or equal to 5%). Regression analyses were performed to generate three formulas for estimating fetal weight on the basis of the following: Gestational age (weeks) + Head circumference (cm) + 2 x Abdominal circumference (cm) + Femur length (cm). This mathematic model allowed formulation of accurate and concise tables relating the sum of these measurements to estimated birth weight. The accuracy of these formulas was then prospectively compared, first, with the formula published by Hadlock et al. (in 32 large-, 279 appropriate-, and 70 small-for-gestational-age fetuses) and second, with the formula of Weiner et al. (in 82 preterm fetuses). The difference between actual and estimated birth weights generated by the three study formulas had no systemic error (t test, p greater than 0.05). Cumulatively, there was a statistically significant reduction of random error in the birth weight estimates by use of the three study formulas versus the best single formulas of Hadlock et al. (2 SD reduced from 21.6% to 19.8% and absolute 2 SD reduced from 15.6% to 12.2%). Additionally, the three study formulas resulted in a statistically significant reduction in the absolute 2 SD error compared with the best formula by Weiner et al. in fetuses less than or equal to 34 weeks' gestation (2 SD reduced from 19.1% to 13.6%).

Ultrasonic growth parameters in fetuses of mothers with primary addiction to cocaine

Sixty-seven women with primary addiction to cocaine were evaluated during their pregnancies by multiple ultrasound studies. Ultrasonic parameters included biparietal diameter, femur length, abdominal circumference, and head circumference. These values were compared with ultrasonic growth parameters in nonaddicted fetuses. Head and abdominal circumference data were used to evaluate the fetuses according to growth pattern. With this system of scoring, subtleties of asymmetric versus symmetric intrauterine growth retardation become apparent. In addition, birth weights of addicted infants were compared with birth weights of nonaddicted infants. The results suggest that, although statistically significant differences in birth weights cannot be demonstrated, abnormal growth of the addicted fetuses does occur. Addicted fetuses show a greater proportion of biparietal diameter and abdominal circumference values below the 50th and 25th percentiles than nonaddicted fetuses, and addicted fetuses more frequently exhibit intrauterine growth retardation patterns. These data suggest that it is fruitful to study these infants with near-normal size but with abnormal intrauterine growth patterns.

Fetal liver measurements by ultrasonography

A total of 378 measurements of fetal liver size were made from 18 weeks gestation through term. Statistical analysis of the results showed a highly significant correlation between fetal liver measurements and gestational age, biparietal diameter, and fetal femur length (R = 0.93, R = 0.89, R = 0.89, respectively). Ultrasonic measurement of the fetal liver is a reliable indicator of fetal growth in the third trimester, as growth rates of the biparietal diameter and head circumference are blunt. Furthermore, consecutive measurements of fetal liver size enhance the detection of symmetrical, fetal growth, by acquisition of various ultrasonic parameters such as biparietal diameter, fetal femur length, fetal abdominal circumference and so forth.

A cross-sectional study of in utero growth of the above average sized fetus

In a cross-sectional study of 210 pregnancies resulting in above-average-sized term infants, biparietal diameter, femur length, and abdominal circumference were found to differ among three birth weight percentile groups (greater than 90, 76 to 90, and 51 to 75). Growth rates, however, were similar. Estimated fetal weights, derived from four formulas, showed the same pattern. Differences between large for gestational age infants and other above average sized infants exist; changes in growth are likely to have occurred before the thirty-third week of gestation.

Accuracy of an average ultrasonic laboratory in measurements of fetal biparietal diameter, head circumference and abdominal circumference

Twenty patients between 14 and 28 gestational weeks were scanned on three occasions during a single day by six operators with different ultrasonic experience (three use a compound scanner and three a real-time equipment). On each occasion every operator had to measure in a "blind" manner the fetal biparietal diameter (BPD), head circumference and abdominal circumference (HC and AC); a coded copy of head and abdominal circumference was subsequently measured by one of the members of the staff. Statistical analysis was carried out on the 1800 measurements, and it was concluded that the accuracy was not dissimilar from that reported by pilot studies. The reproducibility of the parameters studied did not change throughout pregnancy and real-time and compound scanner yielded homogeneous results.

Real-time ultrasound estimations of weight in fetuses of diabetic gravid women

To test the applicability of equations for fetal weight estimations in a group of fetuses suspected of being large for gestational age, real-time ultrasound measurements of fetal biparietal diameters and abdominal circumferences were obtained for 34 fetuses of diabetic mothers. In the first phase of the study the accuracy in the prediction of weight was assessed with use of two known equations. In the second phase, biparietal diameter, abdominal circumference, and actual birth weight data of the 34 study fetuses were used as independent variables to determine the best-fitting equation for relating estimated fetal weight (EFW) to biparietal diameter (BPD) and abdominal circumference (AC); this equation is log (EFW) = 0.02597 AC + 0.2161 BPD - 0.1999 (AC X BPD2)/1000 + 1.2659. The standard deviation of differences is 322.26 gm and multiple R = 0.781. In the final phase the reliability of this equation was compared to those of Thurnau and Shepard in 34 additional fetuses of diabetic gravid women. The data suggest that in these fetuses suspected of being large for gestational age the weight estimates calculated at or near term may be enhanced if predictive equations are formulated specifically from the data for such fetuses.

Use of femur length in estimation of fetal weight

Fetal weight was estimated sonographically within 3 days of delivery in 103 cases. A stepwise regression analysis was performed to evaluate fetal sex, biparietal diameter, head circumference, abdominal circumference, and femur length as factors in estimation of fetal weight. A new formula for calculating fetal weight was derived. Fetal sex did not affect the results obtained. Incorporation of femur length improved the reliability of the weight estimate. Because of intrapopulation and interpopulation differences, institutions using obstetric ultrasound examination techniques should establish their own formulas for estimating fetal weight.

Diminished growth in fetuses born preterm after spontaneous labor or rupture of membranes

We examined biparietal diameter, abdominal circumference, and birth weight in 148 preterm infants to assess fetal growth. A statistically significant proportion of preterm fetuses had biparietal diameter and abdominal circumference values below the fiftieth and tenth percentile levels as compared with that expected in normal fetuses. Similarly, birth weight of infants in the study fell significantly below the fiftieth and tenth percentiles relative to Brenner's curve. We conclude that diminished fetal growth is associated with early delivery secondary to preterm labor or preterm premature rupture of membranes or both. Additionally, since biparietal diameters in preterm fetuses are smaller than those of normal fetuses the prediction of gestational age by cephalometry should be advanced by 7 to 10 days.

Computer assisted analysis of fetal age in the third trimester using multiple fetal growth parameters

A new technique is described for predicting menstrual age in the third trimester of pregnancy (28-42 weeks) using multiple fetal growth parameters (biparietal diameter, head circumference, abdominal circumference, femur length). Evaluation of this technique in 177 normal third trimester pregnancies demonstrated that significant improvement in the variability in predicting menstrual age can be achieved when two or more parameters are used collectively instead of a single parameter used individually. The optimal combination prior to 36 weeks was biparietal diameter, abdominal circumference, and femur length, while after 36 weeks the optimal combination was head circumference, abdominal circumference, and femur length. The use of these combinations resulted in smaller mean errors, standard deviations, and maximum errors. Regression equations and tables of normal values are provided to facilitate the use of this dating method.

Prenatal diagnosis and treatment of intrauterine growth retardation

Prenatal treatment consisting of daytime bedrest, high protein diet and oral administration of allylestrenol was assessed in a prospective study of 30 patients with IUGR infants whose ultrasonically estimated body weight was less than the 10th percentile. In these pregnancies, the gestational age was confirmed in the first trimester, and the fetal weight was estimated from the BPD and AC measurements in the third trimester (Fig. 1). Following treatment, ultrasonic and biochemical determinations were performed. As results: The estimated fetal weight of 1,362 g at 32.9 g gestational weeks increased to 2,678 g at 39.2 weeks on average. The average weekly weight gain was significantly higher than the standard, and 16 cases (53.3%) were more than 10th percentile at birth (Tab. I, Fig. 2). A significant correlation (r = 0.94) between the estimated fetal weight and the birth weight was found. Following prenatal treatments, maternal plasma and urinary estriol, plasma HPL and progesterone increased significantly (Tab. II).

Fetal head and abdominal circumferences: I. Evaluation of measurement errors

Several sources of error associated with the measurement of fetal head and abdominal circumferences (HC, AC) were examined using dynamic image ultrasound. Statistically significant systematic intraobserver errors were not seen unless technical differences in the images were present (HC only) and the range for random errors was 4-5% (2 SD) for both measurements. Although differences in the procedures used to acquire images for measurement had some effect on accuracy (HC only), the primary source of variations in measurements made by different investigators was the measurement methods. Different measuring devices gave different results and different investigators used the same devices differently. Under optimal measuring conditions, the interobserver error for experienced investigators was 1.2 (+/-4.3 SD)% for HC and 2.4 (+/-1.6 SD)% for AC. Comparison of prenatal and postnatal measurements indicated that there were no systematic differences for HC but for AC, the prenatal measurements were 6% greater. Random differences were +/-6% (2 SD) for HC and +/-13% (2 SD) for AC.

Fetal head and abdominal circumferences: II. A critical re-evaluation of the relationship to menstrual age

Dynamic image ultrasound was utilized to re-examine the changes in head and abdominal circumferences (HC, AC) with gestational age in normal fetuses. Data collected in a cross-sectional study of fetal growth were evaluated using mathematical modeling techniques. The results of this analysis indicated that a linear-cubic function optimally fits the HC data (R2 = 97.3%) while the AC data was fitted optimally by a linear function (R2 = 95.5%). The predicted values calculated from these functions were in very close agreement [mean deviation (absolute value): 1.97% (HC), 1.38% (AC)] with those calculated from average functions for HC and AC obtained in a previous longitudinal growth study. Variability was not constant throughout pregnancy for either HC or AC. With HC the normal range changed from +/-1.5 cm to +/-2.5 cm at 28 wk (menstrual age). The AC variability increased progressively with increasing menstrual age and was shown to be related to the predicted AC value. The normal range was found to be 13% of the predicted AC value throughout pregnancy. Based on these results, a new set of normal HC and AC values for the 12-40 wk (menstrual age) period is presented.

Ultrasonic patterns of intrauterine fetal growth in a Latin American country

Head circumference and its cross-sectional area, biparietal and fronto-occipital diameters, abdominal circumference and its cross-sectional area, and the transverse and anteroposterior diameters were measured in 30 healthy single fetuses from normal pregnancies by means of ultrasound. The 5th, 50th and 95th percentiles of distance and velocity curves are described. The comparison of the values of a perimeter (abdominal or cephalic) measured directly from the photograph or calculated by the ellipse formula, showed a straight correlation. The use of the ellipse formula in current practice may simplify and reduce the cost of this technology.

Sonographic abdominal circumference: dynamic versus static imaging

The ultrasonic abdominal circumference (AC) measurement is one of the essential parameters used for assessment of fetal status. Whereas the AC was traditionally derived by static equipment, dynamic scanners are presently used for that purpose. In this study, the AC values obtained by two gray-scale ultrasonic imaging modalities (static and dynamic) were compared; the differences between the mean AC measurements were not statistically significant. Additionally, when the outline of the AC in a fetus near term was larger than the sonic field displayed by dynamic equipment, the partially incomplete boundary could be "filled in" without affecting the accuracy of the result.