Department of Perinatology, Kagawa Medical University, 17501 Ikenobe, Miki, Kagawa 761-0793, Japan
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Abstract |
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Key words: fetal fat deposition/fetal growth/nutrition score/three-dimensional sonography
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Introduction |
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Macrosomic infants (i.e. birthweight >95% for the population) have increased perinatal morbidity, with a higher rate of operative deliveries and trauma with vaginal deliveries (Modanlou et al., 1980). However, defining and identifying macrosomia before delivery has been difficult (Farmer et al., 1992
). Clinical and ultrasound measures have not been sufficiently accurate in predicting fetal weight (Sood et al., 1995
; Johnstone et al., 1996
; Smith et al., 1997
).
To determine the significance of prenatal growth patterns, it is essential that they be related to pregnancy outcome. While outcome could be defined as the physiological status of the infant at birth or the infant's long-term neurological development, it is the anthropometric characteristics of the newborn that can be most directly related to prenatal growth patterns, since similar parameters are measured (Deter, 1995a).
The ponderal index is a measurement of soft-tissue and muscle mass (Miller, 1981; Walther and Ramaekers, 1982
; Hays and Patterson, 1987
; Patterson and Pouliot, 1987
). An asymmetrical growth-restricted infant will have a low ponderal index; a symmetrical small infant will have a normal ponderal index; and a macrosomic infant will have an elevated ponderal index. This index for assessment of neonatal proportions yields more information concerning the nutritional status of the neonate and is relatively independent of the race, gender or menstrual age; therefore, many investigators advocate its use for defining altered fetal growth (Miller, 1981
; Walther and Ramaekers, 1982
; Hays and Patterson, 1987
; Patterson and Pouliot, 1987
). However, it has been reported (Ott, 1990
) that the ponderal index showed a poor correlation with both birth weight for gestational age and projected ideal weight, and that there was no correlation between the occurrence of abnormal fetal heart rate patterns and the ponderal index. It has also been shown (Ariyuki et al., 1995
) that the usefulness of the ponderal index for detection of growth-restricted neonates with poor perinatal outcomes was doubtful.
Direct measurement of parameters related to soft tissue mass [e.g., percentage fat and lean body mass (Fiorotto et al., 1987)] is possible, as well as the use of more clinically applicable indirect methods such as skinfold thickness (Sood et al., 1995
; Abramowicz et al., 1997
) and the nutrition score (Deter and Harrist, 1993a
). The nutrition score is a qualitative procedure for assessing subcutaneous tissue present at four locations (face, ribs, thigh and buttocks), similar in concept to the Apgar score for evaluating the physiological status of the infant at birth. Nutrition score values are in good agreement with the clinical assessment of the nutritional status of the neonate, and malnourished neonates can be separated from well-nourished neonates with a sensitivity of 91.5% and a specificity of 90.7% (Deter and Harrist, 1993a
). Moreover, nutrition score was well correlated with individualized fetal growth assessment (Hata et al., 1991
), and growth-restricted neonates classified by individualized growth assessment showed a significant increase in the low Apgar score (Ariyuki et al., 1995
). A recent study (Hata et al., 1999
) also showed that individualized growth assessment should be useful for detection of small-forgestational-age (SGA) infants with poor perinatal outcomes.
Recent technical development of a three-dimensional (3D) ultrasound machine has led to a self-contained imaging system that can both produce conventional two-dimensional (2D) images and generate within seconds a high-quality 3D image without a need for an external workstation or other additional, costly equipment (Baba et al., 1996, 1997
). Potential obstetric applications of 3D ultrasonography for systematic examination of the developmental stages of the fetus (Hata et al., 1997
, 1998a
,Hata et al., b
), detection of fetal malformations (Merz et al., 1995a
,b
, 1997
; Pretorius et al., 1995
) or birthweight prediction (Lee et al., 1997
) have been reported. To the best of our knowledge, there has been no modality for the assessment of fetal soft tissue deposition and muscle mass in utero. In this study, a novel technique was devised for assessment of fetal soft tissue deposition using 3D ultrasonography, namely, fetal nutrition score, and used to evaluate fetal nutritional status.
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Materials and methods |
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A 3D image was produced by first selecting an ideal representative 2D image placed in the region of interest, and then superimposing on this 2D image a volume box defined by the examiner. The crystal array of the transducer swept mechanically over the defined region of interest through a 60° angle. Within 4 s (128 frames), the outlined volume was automatically scanned and a sculpture-like 3D image was displayed on the screen. In this system, the ultrasound beam was regarded as a projection ray in volume rendering, and ray tracing was conducted in real time; the procedure was not as complex as planar 3D imaging, which requires complex computing and positional information, and so images could be obtained at the end of the scanning sweep (Baba et al., 1996). At present, we use a 128 Mbyte removable hard disk drive for the permanent storage of 3D images.
All 3D examinations of the fetus were done within 1 week before delivery. Within 24 h after delivery, each neonate received an extensive paediatric assessment as described previously (Deter et al., 1987, 1989
, 1996
). Briefly, neonatal growth profile data were evaluated by comparing individual values to appropriate growth curves derived from a cross section of the population. Ponderal index was also calculated. First, one examiner recorded fetal nutrition score in which face, ribs, and buttocks could be adequately seen using 3D ultrasonography (Figure 1
) before delivery, then another examiner recorded modified neonatal nutrition score [face, ribs, and buttocks except for thigh from original neonatal nutrition score (Deter et al., 1990
)]. Both examiners were blinded. Six to 10 3D images were obtained per patient, and the time taken to image the fetal face, ribs, and buttocks was <10 min. On the fetal face, we evaluated orbits, nose, cheek and lips. With respect to the ribs, we depicted fetal chest. On the fetal buttocks, we demonstrated both hips. All 3D ultrasonographic examinations were done by one examiner (M.M.) for the data reported here. The intra-observer coefficient of variation for the assessment of fetal nutritional score was determined by performing five examinations on 10 patients, and the result was 6.2%. Fetal nutrition score was assessed in 20 fetuses by three examiners to evaluate inter-observer variation in the fetal nutrition score values, and results were 9.35 ± 1.72, 9.65 ± 1.59, and 9.45 ± 1.53 respectively (there were no significant differences among three examiners). Linear regression analysis was performed to assess the relationship between modified neonatal nutrition score and fetal nutrition score, ponderal index, birth weight or height, and fetal nutrition score and ponderal index, birth weight, crownheel length, Apgar score value at 1 min or umbilical cord arterial blood pH. P < 0.05 was considered to be statistically significant.
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Results |
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Discussion |
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It is necessary to identify an `abnormal' group on the basis of specific criteria and then define as `abnormal' the values obtained from this group. An `abnormal' group has been defined (Deter and Harrist, 1993b) on the basis of (i) a failure of the neonate to realize its growth potential, (ii) evidence of perinatal morbidity, (iii) a decrease or increase in soft tissue mass at birth and (iv) short- or long-term neurological disabilities. Soft tissue mass is obviously a fetal parameter that would best be measured on the fetal body as a whole (Deter et al., 1995b). Total lean body mass and fat content can be determined in the newborn from conductivity measurements (Fiorotto et al., 1987
) but similar measurements cannot be made in utero. Detailed assessments of fetal growth and organ measurements by means of conventional 2D ultrasonography have been reported (Hata and Deter, 1992
). However, exact evaluation of soft tissue mass is difficult using conventional methods. It has been demonstrated (Hata et al., 1998a
) that 3D ultrasonography revealed the soft tissue deposition of the fetus on the cheeks, abdomen, buttocks and extremities. This study suggests that 3D ultrasonography provides a new method of detecting growth-restricted fetuses and macrosomia. Fetal nutrition score made in this study using 3D ultrasonography was significantly correlated with modified neonatal nutrition score. The nutrition score is a qualitative procedure for assessing subcutaneous tissue of the neonate. Values of this score are in good agreement with the clinical assessment of the nutritional status of the neonate, and malnourished neonates can be clearly separated from well-nourished neonates (Deter and Harrist, 1993a
). Therefore, fetal nutrition score provides a novel means of assessing fetal soft tissue mass in utero. However, fetal nutrition score is a qualitative method, and reproducibility is still an important issue, although there were no significant differences in fetal nutrition score values among three examiners in this study. Further study is needed to clarify the limitations of fetal nutrition score, and it will be interesting to see if there are further studies made in the future.
Original neonatal nutrition score values were determined from a qualitative assessment of the amount of subcutaneous tissue present at four locations (face, ribs, thigh and buttocks) (Deter and Harrist, 1993a). However, fetal nutrition score made in this study was evaluated from fetal subcutaneous tissue present at three locations (face, ribs, and buttocks), and we did not perform a 3D qualitative assessment of the amount of soft tissue mass on the thigh. In the original neonatal nutrition score values, the amount of subcutaneous tissue on the thigh was assessed over the inguinal triangle. One possible factor explaining why it was difficult to assess in utero is that the fetal legs are either adjacent to the inguinal triangle or unseparated, so a thigh could not be visualized over the inguinal triangle. Another possible cause for the inability to show a thigh over the inguinal triangle is that the 3D ultrasonographic machine used in this study consisted of an ultrasonographic scanner specially designed for a ray tracing system (Baba et al., 1996
). Using this system, only one conventional orientation could be used, because the volume could not be rotated. Therefore, fetal position significantly affected the optimal 3D depiction of the thigh.
With respect to limitations associated with 3D ultrasonography, fetal movement required a repeat acquisition to obtain satisfactory data. Moreover, limitations in obtaining optimal visualization of the surface anatomical structures were experienced in the case of inappropriate fetal position. These problems with 3D ultrasound fetal imaging will be resolved as further technical advances are made.
With respect to fetal nutrition score, the minimum score must be 3 and the maximum 15. In this study, most of the points fell between scores 812 for both axes; there were no scores <5 (i.e. 35 group which might include very small/thin babies), and no scores >12 (i.e. 1215 group which would identify very fat/large babies). These extreme groups would be important to include in any future studies. This study was a pilot study to examine normal fetuses, and to obtain a baseline. Therefore, our study naturally leads onto further examination of at risk groups [i.e. very small (score 3) and very large babies (score 15)].
In this study, no significant correlation between ponderal index and fetal nutrition score or modified neonatal nutrition score was evident. Moreover, ponderal index also was not correlated with birth weight and neonatal crownheel length. The current study strongly supports previous studies (Ott, 1990; Ariyuki et al., 1995
), and indicates that ponderal index does not provide any information concerning the nutritional status of the neonate. Our findings will facilitate subsequent investigation to clarify the relationship between fetal nutrition score and fetal growth abnormality, and to determine whether fetal nutrition scores are predictive of perinatal outcomes.
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Acknowledgments |
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Notes |
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References |
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Submitted on June 6, 2000; accepted on July 11, 2000.