Department of Perinatology, Kagawa Medical University, 1750-1 Ikenobe, Miki, Kagawa 761-0793, Japan
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Abstract |
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Key words: appropriate for gestational age infant/fetal growth/multiple fetuses/organ growth/singleton fetus
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Introduction |
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The use of fetal growth curves generated from uncomplicated singleton pregnancies to estimate intrauterine growth of multiple pregnancies is controversial (Weissman et al., 1990). Some studies recommended the use of specific charts generated for twin pregnancies (Grennert et al., 1978
; Sokol et al., 1984
), whereas others conclude that growth curves for singletons may be applied safely for twins, but not for triplets (Sheh et al., 1987
). To the best of our knowledge, there has been no report on the evaluation of singleton, twin, and triplet appropriate for gestational age fetal growth using a longitudinal ultrasound study.
With recent advances in ultrasound imaging, especially improvements in resolution and focusing, fetal intracranial, intrathoracic, and intra-abdominal organs can now be clearly identified (Hata and Deter, 1992). Numerous reports concerned with fetal organ measurements on liver, spleen, and adrenal gland in singleton pregnancies have been presented (Aoki et al., 1992
; Hata et al., 1992
, 1993
; Senoh et al., 1994
). However, there has been no report on these organ growth measurements made with ultrasound in multiple pregnancies.
The objective of our present study was to construct reference limits for various fetal growth parameters from head circumference, abdominal circumference, femur diaphysis length, estimated weight, splenic circumference, adrenal gland circumference, and liver length, based on a longitudinal study of 35 singleton appropriate for gestational age (S-AGA), 18 singleton small for gestational age (S-SGA), 52 twin appropriate for gestational age (Tw-AGA), and 12 triplet appropriate for gestational age (Tri-AGA) infants, and to evaluate the alterations in those growth parameters among these four fetal groups during gestation.
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Materials and methods |
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Birth characteristics of subjects are shown in Table I. Birth weight of 35 S-AGA were in the normal range (between the 10th and 90th percentiles) of the standard growth curve for the Japanese (Sato et al., 1982
), and 18 S-SGA were below normal ranges. Birth weights in Tw-AGA and Tri-AGA infants were compared with the twin weight growth curve for the Japanese (Fukuda, 1989
), and all fetal weights were appropriate for gestational age. The study was approved by the local ethical committee of Kagawa Medical University, and standardized informed consent was obtained from each patient.
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Ultrasound examinations were carried out at 2 week intervals beginning at ~15 weeks of menstrual age continuing until delivery. The number (mean ± SD) of examinations of individual patients ranged from 5 to 13 (9.3 ± 2.1) in the S-AGA group, from 8 to 13 (10.1 ± 1.5) in the S-SGA group, from 5 to 12 (8.0 ± 2.0) in the Tw-AGA group, and from 8 to 10 (9.5 ± 0.9) in the Tri-AGA group. At each examination, each fetus was identified by its position in the uterus, its size, or its sex in multiple pregnancies. Measurements of the biparietal diameter, head circumference, abdominal circumference and femur diaphysis length were obtained at each examination for each fetus using procedures described previously (Deter et al., 1981). The estimated weight was determined from values for the biparietal diameter, abdominal circumference, and femur diaphysis length as described previously (Shinozuka et al., 1987
). The methods used to obtain splenic circumference, liver length, and adrenal gland circumference, measurements have been described in detail elsewhere (Aoki et al., 1992
; Hata et al., 1993
; Senoh et al., 1994
). Unfortunately, fetal organ measurements in triplet pregnancy could not be done, because of fetal crowding and its complexity in the uterus.
Results are expressed as mean ± SD. Statistical analysis for comparison of maternal age, parity, and Apgar score among the groups was done using a KruskalWallis one-way analysis of variance. Maternal height, maternal weight, birth age, birth weight, neonatal crownheel length, neonatal head circumference, neonatal abdominal circumference, and neonatal thigh circumference were compared using an analysis of variance and NewmanKeuls multiple comparison test. P < 0.05 was considered to be significant.
For each parameter in each fetal group data set regression analysis was carried out, testing the regression of the measurement value on menstrual age, using polynomials of the first through the third degree (Dunn and Clark, 1974; Rohatgi, 1976
; Bertagnoli et al., 1983
). Different models were tested and independent variable deletion carried out by analysis of variance applied to the regression was followed by calculation of the step-down method coefficients (Snedecor and Cochran, 1967
). The choice of the optimal model was based on the following criteria: largest R2, all coefficients different from 0, and low standard deviation of regression (SDR ) (Bertagnoli et al., 1983
).
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Results |
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There were no significant differences in predicted splenic circumference (Figure 5) and adrenal gland circumference (Figure 6
) values between S-AGA and Tw-AGA fetuses. However, in S-SGA fetuses, the slopes of the growth curve for splenic circumference and adrenal gland circumference were lower than those in the other two groups with advancing menstrual age. There were slight differences in predicted liver length values between S-AGA, S-SGA and Tw-AGA fetuses, respectively (Figure 7
).
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Discussion |
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There have been only two reports on the growth of triplet fetuses measured by ultrasonography between 15 weeks gestation to delivery (Weissman et al., 1990; Fountain et al., 1995
). However, these two prenatal ultrasound studies were carried out in the USA and UK, respectively. Available data for Asian populations are limited. To the best of our knowledge, there have been no reports on examination of multiple dimensions of fetal growth in multiple pregnancies in the Asian population. It has been stressed (Lei and Wen 1998
) that a different standard of ultrasonography based fetal growth is needed for different populations. Therefore, the ultrasonography-based growth curve constructed in this longitudinal Japanese population provides an additional tool for the evaluation of fetal growth and development in multiple pregnancies.
With respect to fetal organ measurements by ultrasonography in normal twin pregnancy compared to normal singleton pregnancy, there were no significant differences in predicted splenic circumference and adrenal gland circumference values between S-AGA and Tw-AGA fetuses in this study. However, there was a slight difference in predicted liver length value between S-AGA and Tw-AGA fetuses. Similarly, the predicted abdominal circumference value in Tw-AGA fetuses was slightly lower than that in S-AGA fetuses. The liver occupies most of the upper abdominal cavity, so corresponding differences for liver length and abdominal circumference between S-AGA and Tw-AGA fetuses may occur. Our results suggest that growth curves of organ measurements for singletons may be applied safely for twins.
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Notes |
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References |
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Submitted on October 26, 1998; accepted on January 29, 1999.