Longitudinal ultrasonic biometry of various parameters in fetuses with abnormal growth rate

Fetal growth velocity and body proportion in the assessment of growth

Fetal growth restriction implies failure of a fetus to meet its growth potential and is associated with increased perinatal mortality and morbidity. Therefore, antenatal detection of fetal growth restriction is of major importance in an attempt to deliver improved clinical outcomes. The most commonly used approach towards screening for fetal growth restriction is by means of sonographic fetal weight estimation, to detect fetuses small for gestational age, defined by an estimated fetal weight <10th percentile for gestational age. However, the predictive accuracy of this approach is limited both by suboptimal detection rate (as it may overlook non-small-for-gestational-age growth-restricted fetuses) and by a high false-positive rate (as most small-for-gestational-age fetuses are not growth restricted). Here, we review 2 strategies that may improve the diagnostic accuracy of sonographic fetal biometry for fetal growth restriction. The first strategy involves serial ultrasound evaluations of fetal biometry. The information obtained through these serial assessments can be interpreted using several different approaches including fetal growth velocity, conditional percentiles, projection-based methods, and individualized growth assessment that can be viewed as mathematical techniques to quantify any decrease in estimated fetal weight percentile, a phenomenon that many care providers assess and monitor routinely in a qualitative manner. This strategy appears promising in high-risk pregnancies where it seems to improve the detection of growth-restricted fetuses at increased risk of adverse perinatal outcomes and, at the same time, decrease the risk of falsely diagnosing healthy constitutionally small-for-gestational-age fetuses as growth restricted. Further studies are needed to determine the utility of this strategy in low-risk pregnancies as well as to optimize its performance by determining the optimal timing and interval between exams. The second strategy refers to the use of fetal body proportions to classify fetuses as either symmetric or asymmetric using 1 of several ratios; these include the head circumference to abdominal circumference ratio, transverse cerebellar diameter to abdominal circumference ratio, and femur length to abdominal circumference ratio. Although these ratios are associated with small for gestational age at birth and with adverse perinatal outcomes, their predictive accuracy is too low for clinical practice. Furthermore, these associations become questionable when other, potentially more specific measures such as umbilical artery Doppler are being used. Furthermore, these ratios are of limited use in determining the etiology underlying fetal smallness. It is possible that the use of the 2 gestational-age-independent ratios (transverse cerebellar diameter to abdominal circumference and femur length to abdominal circumference) may have a role in the detection of mild-moderate fetal growth restriction in pregnancies without adequate dating. In addition, despite their limited predictive accuracy, these ratios may become abnormal early in the course of fetal growth restriction and may therefore identify pregnancies that may benefit from closer monitoring of fetal growth.

Accuracy of a single fetal weight estimation at 29-34 weeks in diabetic pregnancies: can it predict large-for-gestational-age infants at term?

OBJECTIVES

This study was undertaken to evaluate the accuracy of a single sonographic estimated fetal weight at 29-34 weeks' gestation with respect to birthweight determination in diabetic pregnancies.

STUDY DESIGN

A retrospective cohort study of 423 diabetic pregnancies with detailed fetal measurements at 29-34 weeks' gestation. Multivariate regression analysis was used to predict the birthweight. The percentiles of the estimated fetal weight and the calculated birthweight were compared with the actual birthweight percentile.

RESULTS

The mean birthweight percentile at term was significantly higher than the estimated fetal weight percentile at 29-34 weeks' gestation in the women with poor glycemic control, but not the women with good control. On multivariate analysis, the estimated fetal weight, interval from ultrasound to delivery, hemoglobin A1C level, gestational age at ultrasound, and classification of glycemic control were independently associated with the birthweight. Both the estimated fetal weight and the calculated birthweight had a low sensitivity and a low positive predictive value for predicting large-for-gestational-age infants.

CONCLUSION

Accelerated fetal growth is evident primarily in diabetic women with poor glycemic control. These fetuses cannot be identified by a single ultrasound examination at 29-34 weeks' gestation.

Association of head circumference at birth among sibling pairs

The objective of the study was to estimate and compare the correlation coefficients of head circumference and weight at birth among sibling pairs. Pairs of singleton siblings were ascertained among children born in Norway to the same mother between 1978 and 1997. Head circumference, birthweight and other perinatal factors were registered in the Medical Birth Registry of Norway. Head circumference measurements were obtained for first- and second-born in 287 448 sibling pairs. The correlation coefficient of head circumference among first- and second-born siblings was 0.343 (standard error 0.002) compared with 0.477 (standard error 0.002) for birthweight. These results were similar for later-born sibling pairs and only slightly influenced by other factors such as sex, fatherhood and time between pregnancies. Sensitivity analyses showed that substantial measurement error is required to explain the lower correlation for head circumference. In conclusion, the sibling correlation of head circumference was consistently weaker than that of birthweight.

Fetal growth retardation: associated malformations and chromosomal abnormalities

OBJECTIVE

Our objective was to determine the incidence and pattern of chromosomal abnormalities in fetal growth retardation.

STUDY DESIGN

Blood karyotyping was performed in 458 fetuses referred to us for further assessment of growth retardation at 17 to 39 weeks' gestation.

RESULTS

The fetal karyotype was normal in 369 and abnormal in 89 (19%) of the cases. The most common chromosomal defect in the group referred at < 26 weeks' gestation was triploidy; in those referred at > or = 26 weeks, it was trisomy 18. The incidence of fetal autosomal chromosome aberrations increased, whereas the incidence of triploidy did not change, with maternal age. Ninety-six percent of chromosomally abnormal fetuses had multisystem fetal defects that were characteristic of the different types of chromosomal abnormalities. Compared with those fetuses with a normal karyotype, the chromosomally abnormal group had a higher mean head circumference/abdominal circumference ratio, a higher incidence of normal or increased amniotic fluid volume, and normal waveforms from the uterine or umbilical arteries or both.

CONCLUSION

The findings of the different types of chromosomal abnormalities and their ultrasonographically detectable phenotypic expression provide the background for prospective studies to determine the incidence of chromosomal abnormalities in unselected populations of small-for-gestational-age fetuses.

Fetal growth disturbances

IUGR is a fetal disorder characterized by diminished fetal growth, especially in the third trimester. Growth retardation may be due to primary placental insufficiency or may result from a variety of maternal or fetal causes and is associated with elevated perinatal mortality and morbidity. Numerous conventional and Doppler ultrasound criteria have been proposed for diagnosing IUGR prenatally, but none on its own permits confident diagnosis of this condition. Diagnosis or exclusion of IUGR can best be achieved by the combined use of three parameters: estimated fetal weight, amniotic fluid volume, and maternal hypertension. When IUGR is suspected based on these parameters, Doppler ultrasound can help to determine the prognosis. Large fetuses, particularly those weighing more than 4,000 grams at birth, are at risk for perinatal morbidity and mortality due to obstetrical complications. These fetuses occur more frequently and are at especially high risk in diabetic mothers. The estimated fetal weight is the most direct parameter for diagnosing LGA and macrosomia and is moderately accurate with positive predictive values up to 67% in the general population and 77% in diabetics. It can be an important factor in deciding on the route of delivery in diabetic mothers.

The differential neonatal morbidity of the intrauterine growth retardation syndrome

This is a prospective study of differential morbidity among subgroups of intrauterine growth retardation. Cases of intrauterine growth retardation (N = 3450) (greater than or equal to 37 weeks, less than 10th percentile birth weight for gestational age) were classified by their ponderal index (weight/length3) in four subgroups using the 10th, 25th, and 90th percentiles of the Lubchenco's ponderal index-gestational age distribution. There were 432 cases (12.5%) with low ponderal index or disproportionate intrauterine growth retardation, 936 (27.1%) with intermediate ponderal index, 2030 (58.8%) with adequate ponderal index or proportionate intrauterine growth retardation, and 52 (1.5%) with high ponderal index. The low ponderal index group or disproportionate intrauterine growth retardation group had a statistically significant higher risk (between 1.6 and 12.5 times) for low 1- and 5-minute Apgar scores, aspiration syndrome, hypoglycemia, and perinatal asphyxia than the adequate ponderal index group. The low ponderal index group also had an increased risk (relative risk = 2.0 [95% confidence interval, 1.0 to 3.8]) for hospital stay of more than 1 week. These differences persist after a stratified analysis by birth weight and in a multiple logistic regression analysis. Similarly, higher neonatal morbidity is observed among infants with normal birth weights but with low ponderal index. These data provide further evidence of the heterogeneity of the intrauterine growth retardation syndrome and of the independent effect of body disproportion on neonatal morbidity, even among infants with normal birth weights. Because there are significant clinical implications attributed to the low ponderal index group, this subgroup should be identified as early as possible.