Intrauterine sonographic assessments of embryonic heart diameter

Human Reproduction vol.12 no.10 pp.2286 2291, 1997 Intrauterine sonographic assessments of embryonic heart diameter Toshiyuki Hata 1, Daisaku Senoh, Kohkichi Hata and Kohji Miyazaki Department of Obstetrics and Gynecology, Shimane Medical University, Izumo 693, Japan 1 To whom correspondence should be addressed Our purpose was to evaluate embryonic heart diameter in early first-trimester pregnancy using intrauterine sonography with a 20 MHz flexible catheter-based highresolution real-time miniature transducer. A total of 40 women about to undergo therapeutic abortion from 6 9.9 weeks gestational age and one abnormal pregnancy with fetal hydrops at 9 weeks were studied with a specially developed catheter-based high-resolution real-time miniature (2.4 mm outer diameter) ultrasound transducer (20 MHz). A curvilinear relationship was found between the menstrual age and embryonic heart diameter (R 2 95.7%), and a normal range of embryonic heart diameter for estimating the growth of the embryonic heart during early first-trimester pregnancy was generated. A normogram of menstrual age as predicted by embryonic heart diameter was also established. There was a good curvilinear correlation between embryonic heart diameter and crown rump length (R 2 90.1%). The embryonic heart diameter/ crown rump length ratio rapidly decreased from week 6 to week 7, and remained almost constant thereafter. Embryonic heart diameter (5.2 mm) in the case of fetal hydrops at 9 weeks was above the normal range. These results may provide an additional method of estimating gestational age in the early first trimester of pregnancy. In this limited series, a single case of embryonic heart enlargement was demonstrated, suggesting its potential use in the detection of embryonic congestive heart failure. Key words: embryo/growth/heart/intrauterine sonography Introduction There have been few reports on the growth of the embryonic and fetal heart as measured by ultrasonography in the firstand early second-trimester pregnancies (Bronstein et al., 1992; Blaas et al., 1995a). The cardiovascular system begins to develop during the first 5 weeks of menstrual age from splanchnic mesoderm in the cardiogenic area. Paired endocardial heart tubes form and fuse into a single heart tube, the primitive heart. By the end of 5 weeks, a functional cardiovascular system is present. As the heart tube grows, it bends to the right and soon acquires the general external appearance of the adult heart. The heart becomes partitioned into four chambers at 6 9 weeks (Moore, 1982). The critical period of heart development is from ~week 5 to week 9. There are numerous critical events during cardiac development, and deviation from the normal pattern at any one time may produce one or more cardiac defects (Moore, 1982). There have been numerous reports on the antenatal diagnosis of congenital heart disease by transvaginal sonography in late first-trimester pregnancy (Bronstein et al., 1993; Gembruch et al., 1993; Achiron et al., 1994). However, to the best of our knowledge, a detailed description of embryonic heart growth in the early first trimester of pregnancy has not yet been published. Visualization of anatomical structures of the normal human embryo using flexible catheter-based high-resolution real-time ultrasound transducers has been reported (Ragavendra et al., 1991, 1993). Fujiwaki et al. (1995) demonstrated that intrauterine sonography could reveal embryonic structures 1 3 weeks earlier than transvaginal sonography. Moreover, it was possible to obtain finer quality images of very small embryonic structures with intrauterine sonography than with transvaginal sonography. The objective of the current study was to evaluate embryonic heart growth during early first-trimester gestation using intrauterine sonography with a flexible catheter-based high-resolution real-time miniature transducer. Materials and methods A total of 40 women (five at week 6, 16 at week 7, nine at week 8, and 10 at week 9) about to undergo therapeutic abortion at 6 9.9 weeks gestational age and one abnormal pregnancy with fetal hydrops at 9 weeks were studied with a specially developed catheter-based high-resolution real-time miniature (2.4 mm in outer diameter) ultrasound transducer (20 MHz, Aloka AMP-PN20 08L; Aloka Co, Tokyo, Japan). Subjects were randomly recruited over a 10 month period from March 1996. The depth of penetration of the ultrasound beam is ~2 cm. This ultrasonic catheter is connected to an ultrasound device (Aloka SSD-550; Aloka Co). A motor in the main imaging device (Aloka ASU-100; Aloka Co) rotates the metal drive shaft at 900 r.p.m., resulting in a 360 real-time grey-scale image oriented perpendicularly to the long axis of the ultrasonic catheter. The frame rate used during the examination was 15/s. All examinations were performed by one person (T.H.). The study was approved by the local ethical committee of Shimane Medical University, and standardized informed consent was obtained from each patient. Before each procedure, the intrauterine location of the embryo was confirmed by transabdominal or transvaginal sonography. Each patient was prepared and draped in the usual sterile fashion in the dorsolithotomy position. A sterile speculum was inserted into the vagina. The ultrasonic catheter was introduced gently through the cervix and into the endometrial cavity until it could not be advanced any further. Once within the endometrial cavity, the catheter tip was advanced or withdrawn slightly until the embryo was visualized. 2286 European Society for Human Reproduction and Embryology

Embryonic heart diameter Figure 1. A coronal view of embryo at 7 weeks. H head; LA left atrium; LV left ventricle; RA right atrium; RV right ventricle. Figure 2. A horizontal thoracic view of embryo at 9 weeks 5 days. LA left atrium; LV left ventricle; RA right atrium; RV right ventricle. We initially studied 52 women about to undergo therapeutic abortion at 6 9.9 weeks gestation with transabdominal or transvaginal sonography. The gestational age by menstrual history was compared with that by the crown rump length (CRL) (Iwamoto, 1983). Only those cases with a discrepancy that was less than 3 days were included in the present study. Cases (n 12; two at week 6, four at week 7, five at week 8, and one at week 9) were excluded from the study because the discrepancy was 3 days. Therefore, a total of 40 women were scanned using intrauterine sonography after the CRL measurements were found to be within a range of 3 days from menstrual age. In the coronal or horizontal thoracic view of the embryo, the heart size (embryonic heart diameter, EHD) was measured in the largest transverse diameter, at the level of the atrioventricular valves (Figures 1 and 2). It was possible to distinguish between systole and diastole. The measurements of the embryonic heart were based on the outer/ outer diameter, i.e. from the epicardial lining to the opposite epicardial lining in diastole. The data set contained only one measurement per patient to provide a cross-sectional analysis. After database screening with tests for a normal distribution, a growth curve for the EHD was determined for the cross-sectional data. Data set regression analysis was carried out, testing the regression of heart measurement on menstrual age (MA) or CRL using polynomial equations of the first through the third degree (Dunn and Clark, 1974; Rohatgi, 1976; Bertagnoli et al., 1983). The different methods were tested and independent variable deletion carried out by analysis of variance applied to the regression, 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 R 2, all coefficients different from 0, and low SD of regression (SD R ) (Bertagnoli et al., 1983). Pathological examination, chromosome analysis, and EHD and CRL measurements post abortum could not be performed, because the embryos were damaged during the performance of the therapeutic abortion. 2287

T.Hata et al. Table I. Normal range of embryonic heart diameter Menstrual age (days) Embryonic heart diameter (mm) Figure 3. Embryonic heart diameter as a function of menstrual age. 44 0.3 0.8 1.3 45 0.5 1.0 1.5 46 0.7 1.2 1.7 47 0.9 1.4 1.9 48 1.0 1.5 2.1 49 1.2 1.7 2.2 50 1.4 1.9 2.4 51 1.6 2.1 2.6 52 1.7 2.2 2.7 53 1.9 2.4 2.9 54 2.1 2.6 3.1 55 2.2 2.7 3.2 56 2.4 2.9 3.4 57 2.5 3.1 3.6 58 2.7 3.2 3.7 59 2.9 3.4 3.9 60 3.0 3.5 4.0 61 3.1 3.7 4.2 62 3.3 3.8 4.3 63 3.4 3.9 4.4 64 3.6 4.1 4.6 65 3.7 4.2 4.7 66 3.8 4.3 4.8 67 3.9 4.4 4.9 68 4.1 4.6 5.1 69 4.2 4.7 5.2 70 4.3 4.8 5.3 *Embryonic heart diameter 4.4715 0.0041955(MA) 2 0.00003298(MA) 3. MA menstrual age; regression SD 0.2524. Figure 4. Embryonic heart diameter as a function of crown rump length. Results There was no difficulty in passing the imaging catheter through the cervix into the endometrial cavity. Neither bleeding nor leakage of amniotic fluid from the external cervical os was seen after removal of the catheter. There were no known immediate complications. Seven cases (2 at week 7, 1 at week 8, and 4 at week 9) were excluded from the study because of the shallow scanning range of high-frequency transducers or inappropriate embryonic position. From the results of the mathematical modelling of the data, the optimal models for EHD are as follows (EHD and CRL in mm and MA in days): EHD 4.4715 0.0041955(MA) 2 0.00003298(MA) 3, R 2 95.2% (Figure 3) EHD 1.113 0.013434(CRL) 2 0.00030094(CRL) 3, R 2 90.1% (Figure 4) 2288 The predicted values of EHD derived from these functions and variabilities at different MAs or CRLs are presented in Tables I and II. The coefficient of variation of EHD was 6.4%. The equation describing the relationship between EHD/CRL ratio and MA is as follows (MA in days): EHD/CRL 3.7294 0.11567(MA) 0.00093918(MA) 2, R 2 48.4% (Figure 5) A normogram of EHD/CRL ratio as predicted by MA was generated (Table III). The equation describing the relationship between MA and EHD is as follows (MA in days and EHD in mm): MA 44.2394 1.8737(EHD) 2 0.16409(EHD) 3, R 2 95.7% (Figure 6) A normogram of menstrual age as predicted by EHD was generated (Table IV). In the abnormal pregnancy with fetal hydrops (generalized skin oedema, bilateral pleural effusion and pericardial effusion) at 9 weeks, EHD (5.2 mm) was significantly large. Discussion The embryonic period, which ranges from 4 to 8 weeks from the last menstrual period, is very important for human development, because most major anatomical structures begin to develop during these 5 weeks. The cardiovascular system is the first system to function in the embryo; blood begins to circulate by the end of 5 weeks of menstrual age. This precocious development is essential because the rapidly grow-

Embryonic heart diameter Table II. Embryonic heart diameter at each crown rump length Crown rump length (mm) Embryonic heart diameter (mm) 2 0.4 1.2 1.9 3 0.5 1.2 1.9 4 0.6 1.3 2.0 5 0.7 1.4 2.1 6 0.8 1.5 2.3 7 0.9 1.7 2.4 8 1.1 1.8 2.5 9 1.3 2.0 2.7 10 1.4 2.2 2.9 11 1.6 2.3 3.1 12 1.8 2.5 3.3 13 2.0 2.7 3.4 14 2.2 2.9 3.6 15 2.4 3.1 3.8 16 2.6 3.3 4.0 17 2.8 3.5 4.2 18 3.0 3.7 4.4 19 3.2 3.9 4.6 20 3.4 4.1 4.8 21 3.5 4.2 5.0 22 3.7 4.4 5.1 23 3.8 4.6 5.3 24 4.0 4.7 5.4 25 4.1 4.8 5.5 26 4.2 4.9 5.6 27 4.3 5.0 5.7 28 4.3 5.0 5.8 29 4.3 5.1 5.8 *Embryonic heart diameter 1.1113 0.013434(CRL) 2 0.00030094(CRL) 3. CRL crown rump length; regression SD 0.3629. Table III. Normal range of embryonic heart diameter/crown rump length (EHD/CRL) Menstrual age (days) EHD/CRL 44 0.30 0.46 0.61 45 0.27 0.43 0.58 46 0.24 0.40 0.55 47 0.21 0.37 0.52 48 0.19 0.34 0.49 49 0.16 0.32 0.47 50 0.14 0.29 0.45 51 0.12 0.27 0.43 52 0.10 0.25 0.41 53 0.08 0.24 0.39 54 0.07 0.22 0.38 55 0.05 0.21 0.36 56 0.04 0.20 0.35 57 0.03 0.19 0.34 58 0.03 0.18 0.33 59 0.02 0.17 0.33 60 0.02 0.17 0.32 61 0.01 0.17 0.32 62 0.01 0.17 0.32 63 0.02 0.17 0.32 64 0.02 0.17 0.33 65 0.02 0.18 0.33 66 0.03 0.19 0.34 67 0.04 0.20 0.35 68 0.05 0.21 0.36 69 0.07 0.22 0.37 70 0.08 0.23 0.39 *EHD/CRL 3.7294 0.11567(MA) 0.0009391(MA) 2. MA menstrual age; regression SD 0.07681. Figure 5. Embryonic heart diameter (EHD)/crown rump length (CRL) ratio as a function of menstrual age. ing embryo needs an efficient method of acquiring nutrients and disposing of waste products (Moore, 1982). There has been only one report on the growth of the embryonic heart measured by transvaginal sonography between 7 weeks to 12 weeks of gestation (Blaas et al., 1995a). These authors used a linear function to characterize the growth of EHD (R 2 Figure 6. Menstrual age as a function of embryonic heart diameter. 85%). In this investigation, we used intrauterine sonography with 20 MHz flexible catheter-based high-resolution real-time miniature transducer, and it was possible to visualize very small embryonic hearts even in the early first trimester of pregnancy. Therefore, the curvilinear function used in this investigation gave a better fit for EHD (R 2 95.2%) than the function used by Blaas et al. (1995a). However, EHD could not be obtained in seven out of 40 cases (17.5%) in this study. 2289

T.Hata et al. Table IV. Menstrual age at each embryonic heart diameter Embryonic heart diameter (mm) Menstrual age (days) 0.7 42 45 48 0.8 42 45 48 0.9 43 46 49 1.0 43 46 49 1.1 43 46 49 1.2 44 47 50 1.3 44 47 50 1.4 44 47 51 1.5 45 48 51 1.6 45 48 51 1.7 46 49 52 1.8 46 49 52 1.9 47 50 53 2.0 47 50 54 2.1 48 51 54 2.2 48 52 55 2.3 49 52 55 2.4 50 53 56 2.5 50 53 57 2.6 51 54 57 2.7 52 55 58 2.8 52 55 58 2.9 53 56 59 3.0 54 57 60 3.1 54 57 60 3.2 55 58 61 3.3 56 59 62 3.4 56 59 63 3.5 57 60 63 3.6 58 61 64 3.7 58 62 65 3.8 59 62 65 3.9 60 63 66 4.0 61 64 67 4.1 61 64 68 4.2 62 65 68 4.3 63 66 69 4.4 63 67 70 4.5 64 67 70 4.6 65 68 71 4.7 65 69 72 4.8 66 69 72 4.9 67 70 73 5.0 67 71 74 *Menstrual age 44.2394 1.8737(EHD) 2 0.16409(EHD) 3. EHD embryonic heart diameter; regression SD 1.554 One reason for this low detection rate was the depth of penetration of the transducer beam with high ultrasound frequency (20 MHz). The depth of penetration of the ultrasound beam is ~2 cm, so this might be sufficient to evaluate embryos of 20 mm, but examination of larger embryos was markedly limited (Fujiwaki et al., 1995; Hata, 1996; Hata et al., 1996). Intrauterine sonography appears to lack the manoeuverability, deep beam penetration, and the ability to allow perpendicular planes of section to be obtained. The ultrasound measurements of small embryonic structures are associated with an elevated intraobserver variability (Blaas et al., 1994, 1995b). In this study, all examinations were performed by one person (T.H.) with great experience of intrauterine sonography, in order to reduce intra-observer variability. Consequently, a good coefficient of variation for EHD measurements (6.4%) was obtained. In a previous study, the reduced reproducibility 2290 of measuring small embryonic structures and/or the large biological variation of parameters resulted in reduced values of R 2 (Blaas et al., 1995a). However, high R 2 values for EHD measurements were obtained in the present study. Compared with body size, the heart is relatively large in the early embryonic period, becoming a relatively smaller part of the embryo with increasing age (Blaas et al., 1995a). Clark (1985) found a 15-fold increase of the chick embryonic dry weight compared with a nine-fold increase in heart weight from 3 days to 6 days of gestational age, and he concluded that the larger the embryo, the smaller the relative size of the heart. Blaas et al. (1995a) reported that the EHD/CRL ratio as determined by ultrasound between 7 and 9 weeks was almost constant. In the present study, the EHD/CRL ratio decreased significantly from 6 to 7 weeks and remained almost constant thereafter. These results suggest that there is a considerable change in the relationship between the heart size and the body size in the early first trimester of pregnancy. Until now, the CRL measurement has been the most accurate predictor of gestational age in the first trimester (Robinson, 1973; Robinson and Fleming, 1975). Our previous investigations (Hata et al., 1996) demonstrated that the growth of the embryonic liver length is similar to that of the CRL and provides an additional means of estimating gestational age in the first trimester. The coefficient of determination of the second-degree polynomial equation between embryonic liver length and gestational age was very high (R 2 93.7%). In this study, the coefficient of determination of curvilinear equation between EHD and gestational age was also very high (R 2 95.7%). Therefore, adjunctive utilization of EHD measurement to estimate age may serve to confirm or reject information derived from CRL determination. However, the population was preselected on the basis of a good correlation between gestational age and CRL. Bessho et al. (1995) reported that chromosomal anomalies cause the majority of first-trimester miscarriages. In this study, one fetal hydrops at 9 weeks could be diagnosed in utero with both transvaginal sonography and intrauterine sonography. However, it was possible to obtain finer quality images of very small embryonic structures with intrauterine sonography than with transvaginal sonography. Intrauterine sonography clearly depicted heart enlargement at 9 weeks, and this may be the first case of cardiomegaly diagnosed during the embryonic period. Unfortunately, pathological examination and chromosome analysis could not be performed because the embryo was damaged during the therapeutic abortion. With regard to the limitations of intrauterine sonography, it is an invasive diagnostic procedure requiring sterile conditions. Its safety has not yet been established. Although neither we, nor previous authors (Ragavendra et al., 1991, 1993; Fujiwaki et al., 1995; Hata et al., 1996), have encountered any immediate complications, its use is not recommended for routine clinical examination at present. In conclusion, intrauterine sonography provides additional information on the estimation of gestational age in the early first trimester of pregnancy. In this limited series one embryonic heart enlargement was demonstrated and, thus, there is a potential for its use in the detection of embryonic cardiac

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