Estimating fetal age: computer-assisted analysis of multiple fetal growth parameters.

Abstract

Regression models for predicting menstrual age based on real-time sonographic measurements of four fetal parameters (biparietal diameter, head circumference, abdominal circumference, and femur length), used alone and in combination, were developed in a cross-sectional study of 361 fetuses between 14 and 42 menstrual weeks. The head circumference and femur length were the strongest individual predictors of age. A number of combinations of fetal parameters, including the combination of head circumference and femur length, provided age estimates that were significantly better (p = 0.05) than those using any single parameter alone. It was also demonstrated that simply averaging individual age estimates in a given case could provide results that were not significantly different from those obtained by using the same parameters in a complex regression equation. The advantages and potential pitfalls of this system of fetal dating are discussed.

Ultrasonography of the fetal thyroid: nomograms based on biparietal diameter and gestational age.

“…Such information may be useful in the absence of a well-dated pregnancy or possibly if the fetus is large or small for gestational age. Previously published gestational ageindependent nomograms include BPD as a predictor of fetal age, 13 head circumferenceabdominal circumference ratio, 14 and BPD-long bone ratios for Down syndrome screening. 15 Biparietal diameter-and gestational age-based nomograms may be used to assess fetal thyroid size in patients who are at risk for fetal goiter, enabling the examiner to evaluate the possibility of thyroid abnormality in the fetus and to assess fetal thyroid size after intrauterine treatment.…”

Ultrasound of the fetal thymus.

“…Dating of each pregnancy was based on multiple fetal growth parameters, 4 earlier ultrasound if available, or reliable menstrual history. The frequency of sonographic visualization of the thymus was assessed.…”

Evaluation of femur length during the second and third trimesters in fetuses with myelomeningocele

“…These latter findings have been well documented in prior studies 4 , and the fact that our study detected these known changes suggests that our methodology was valid. Other researchers have also used our method of comparison of gestational age based on last menstrual period with gestational age predicted from biometric measurements using Hadlock's tables 9,10 . One could also speculate that postnatal lower extremity growth measurements might be a potential outcome measure after fetal surgery for myelomeningocele 11,12 , given the absence of shortening of the femur in the second or third trimester.…”

“…Ultrasound data were collected at routine secondtrimester scans and included femur length, biparietal diameter and head and abdominal circumferences. These parameters were recorded as predicted gestational age based on Hadlock's tables 9,10 . The level of the spinal defect as determined by ultrasound examination was recorded in the fetuses with myelomeningocele.…”