先天性心脏病胎儿脑血流动力学变化的临床研究

目的 探讨先天性心脏病(CHD)对胎儿脑血流动力学的影响,及不同类型CHD对脑血流动力学的影响程度.方法 正常胎儿200例和产前超声心动图诊断为CHD胎儿159例,其中左心发育不良综合征(HLHS)23例,左心梗阻性病变(LSOL)19例,右心发育不良综合征(HRHS)15例,右心梗阻性病变(RSOL)33例,间隔缺损36例,圆锥动脉干畸形(CTD)33例.测量胎儿大脑中动脉搏动指数(MCA-PI)、脐动脉搏动指数(UA-PI)及脑/脐血管PL管PI比值(CPR).结果 HLHS、HRHS、RSOL、CTD及SD组胎儿的MCA-PI和CPR均较对照组减低,UA-PI均较对照组升高,差异均有统计学意义(P<0.05);LSOL组的各参数与对照组比较差异均无尤统计学意义(P>0.05).结论 宫内CHD胎儿出现脑血管阻力下降,不同类型CHD脑血管阻力的改变程度不同,提示不同类型CHD胎儿存在不同程度的脑循环代偿反应.     

功能性单心室合并大动脉梗阻胎儿的脑血流改变

目的 探讨功能性单心室（FSV）合并大动脉梗阻胎儿的脑血流改变。方法 收集经超声心动图诊断为FSV的胎儿40胎（病例组）,正常胎儿65胎（对照组）。采用脉冲多普勒超声检测胎儿大脑中动脉（MCA）和脐动脉（UA）,计算MCA搏动指数（MCA-PI）、UA搏动指数（UA-PI）和脑/脐血管阻力指数比（CPR）。先将MCA-PI与UA-PI进行Z分数换算,再进行统计学分析。结果 病例组40胎FSV中,23胎FSV合并主动脉梗阻（FSV合并主动脉梗阻亚组）,17胎FSV合并肺动脉梗阻（FSV合并肺动脉梗阻亚组）。病例组与对照组MCA-PI Z分数、UA-PI Z分数、CPR差异均无统计学意义（P>0.05）。FSV合并主动脉梗阻亚组MCA-PI Z分数值低于对照组及FSV合并肺动脉梗阻亚组（P<0.05）。FSV合并肺动脉梗阻亚组MCA-PI Z分数值高于对照组（P<0.05）。3组UA-PI Z分数值差异无统计学意义（P>0.05）。FSV合并主动脉梗阻亚组CPR值低于对照组及FSV合并肺动脉梗阻亚组（P<0.05）,FSV合并肺动脉梗阻亚组CPR值与对照组差异无统计学意义（P>0.05）。结论 FSV合并主动脉梗阻和FSV合并肺动脉梗阻的胎儿脑血流改变不同,且存在不同程度的脑循环代偿反应。     

三维超声检测双胎输血综合征胎儿产尿率比值的价值

目的 探讨双胎输血综合征(TTTS)胎儿产尿率(UPR)比值的临床价值.方法 8例TTTS胎儿为病例组,选择同期进行连续性超声检查的22例单绒毛膜双羊膜腔(MCDA)双胎作为正常对照组.采用三维超声计算机辅助虚拟脏器分析(VOCAL)测量两组胎儿UPR并计算双胎间UPR比值.结果 ①不同孕周正常MCDA双胎UPR比值较恒定,为0.97±0.28;胎儿UPR比值与孕周的相关系数为0.13,UPR比值与孕周无明显相关性.②与正常MCDA双胎比较,TTTS胎儿UPR受/UPR供比值明显增高(7.83±2.61,t=6.19,P＜0.05).结论 胎儿UPR比值是评估TTTS胎儿的一项重要指标.     

三维超声检测妊娠期高血压疾病和宫内生长受限胎儿的产尿率

目的 研究妊娠期高血压疾病和宫内生长受限(intrautrine growth restriction,IUGR)胎儿产尿率(urine production rate,UPR)的改变情况.方法 应用三维超声虚拟器官计算机辅助分析(virtual organ computer-aided analysis,VOCAL)技术,测量53例正常单胎妊娠、47例妊娠期高血压疾病及47例IUGR胎儿的膀胱体积并计算各组胎儿UPR,经过Z-score转换消除孕周影响,测得的病例组Z值分别与对照组Z值进行比较.结果 妊娠期高血压组与对照组胎儿UPR之间差异无统计学意义(Z值分别为-0.43±0.30和-0.28±0.48; P＞0.05);轻度与重度子痫前期组胎儿UPR逐渐减低(Z值分别为-0.65±0.20和-1.09±0.57),与对照组均有显著性差异(均P＜0.01).IUGR组胎儿UPR(Z值为-1.13±0.61)明显低于对照组(P＜0.001).结论 妊娠期高血压疾病和IUGR胎儿有不同程度的UPR减低,认为可能与胎儿慢性宫内缺氧及其程度有关.     

先天性心脏病胎儿胎盘病理学改变

目的 探讨先天性心脏病(CHD)胎儿胎盘的病理学改变。方法 回顾性分析89胎CHD胎儿(CHD组)及111胎正常胎儿(对照组)的产前超声资料、胎盘病理检查结果及相关临床资料，观察组间胎盘病理改变、胎盘质量(P wt)、胎儿出生或引产时体质量(B wt)及P wt/B wt比值的差异。结果 CHD组胎盘炎症2级、脐血管炎、合体细胞结节增多、边缘型脐带胎盘插入及单脐动脉发生率均高于、而钙化灶发生率及成熟胎盘比例均低于对照组(P均<0.05)。CHD组P wt、B wt均低于、而P wt/B wt比值高于对照组(P均<0.05)。CHD组7.87%(7/89)胎儿P wt/B wt比值大于对应孕周P wt/B wt比值第90百分位，对照组为1.80%(2/111),组间差异有统计学意义(P<0.05)。结论 CHD胎儿胎盘存在灌注不良、高级别胎盘炎症及功能不全等病理学改变。     

产前MRI量化评价先天性心脏病胎儿脑二维径线

目的 观察产前MRI量化评价先天性心脏病胎儿脑二维径线的价值。方法 150名孕龄（GA）21~39周孕妇（150胎）接受产前胎儿MR检查，其中50胎先天性心脏病（CHD）胎儿（CHD组），GA平均（28.05±4.50）周，包括27胎<28周、23胎≥28周；100胎脑发育正常（对照组），GA平均（27.85±4.40）周，包括48胎<28周、52胎≥28周。行单次激发自旋回波（SSTSE）序列扫描，测量胎儿脑双顶径（BBD）、脑额枕径（BFOL）、骨双顶径（SBD）、骨枕额径（SOD）及头围（HC），并以快速平衡稳态梯度回波（B-FFE）序列显示胎儿心血管结构。对胎儿颅脑主要二维径线指标与GA进行相关性分析，得到拟合直线，分析2组胎儿相关指标的差异。结果 2组胎儿BBD、BFOL、SBD、SOD、HC与GA均呈高度线性相关（CHD组r=0.96、0.89、0.94、0.90、0.93，P均<0.01；对照组r=0.97、0.96、0.94、0.95、0.95，P均<0.01）。<28周胎儿组间径线指标差异均无统计学意义（P均>0.05）；≥28周胎儿中，CHD组BBD、BFOL、SOD和HC均小于对照组（P均<0.05），SBD差异无统计学意义（P=0.10）。结论 MRI量化评价胎儿颅脑生物学指标可为宫内评估胎儿大脑生长发育情况提供参考。CHD在宫内即可影响胎儿脑发育；中晚孕期CHD胎儿BBD、BFOL、SOD和HC均相对减小。     

三维超声测量胎儿肺体积及其在常见胎儿肺病变随访中的应用

目的利用三维超声技术测量胎儿肺体积,建立肺体积正常值范围,评价胎儿肺发育。方法选择显示满意的300胎18～36周正常胎儿肺三维容积图像,利用VOCAL技术测量其左、右肺体积,并对肺总体积(TLV)与孕周(GA)进行回归分析。随机抽取20胎正常胎儿TLV测值进行可信度分析。对4胎超声诊断为肺囊性腺瘤样畸形或隔离肺胎儿进行随访,测量其TLV,与正常胎儿TLV行散点图比较,观察其变化趋势。结果胎儿肺三维图像满意者占91.74%(300/327)。正常胎儿TLV随GA增加而增大,最适回归方程为:TLV=1.139-1.418GA+0.093GA2(r=0.99,P<0.01)。三维超声测量胎儿TLV的可信度很高(内部一致性系数为0.99,组内相关系数为0.99)。4胎肺病变胎儿TLV均随GA增加而增大,但变化趋势各不相同。结论三维超声能够很好地测量胎儿肺体积,在评价胎儿肺发育中具有重要作用。     

超声评估复杂型先天性心脏病胎儿脑发育

目的:采用二维和频谱多普勒超声测量先天性心脏病(congenital heart disease,CHD)胎儿脑沟的深度及脑血流参数,以评估CHD胎儿脑发育情况。方法:选取2016年6月至201 8年6月于保定市第一中心医院行产前超声检查,发现复杂型CHD胎儿34例。同时选取同孕周超声检查正常胎儿34例为对照组。分别测量正常组和CHD组胎儿大脑中动脉搏动指数(middle cerebral artery pulsatility index,MCAPI)、脐动脉搏动指数(umbilical artery pulsatility index,UAPI)、脑-胎盘比(cerebroplacental ratio,CPR)、顶枕沟深度、外侧裂深度、距状沟深度,比较两组间各参数的差异。采用新生儿行为神经测定(neonatal behavioral neurological assessment,NBNA)量表评估新生儿脑损伤情况,比较两组间NBNA评分差异,分析二维及频谱超声各参数测值与NBNA评分的相关性。结果:CHD组胎儿MCAPI,UAPI,CPR,顶枕沟深度,外侧裂深度,距状沟深度与正常组比较差异有统计学意义(P0.05);正常组与16例CHD组新生儿NBNA评分比较差异有统计学意义(P0.05);二维及频谱超声各参数测值与NBNA有一定的相关性(P0.05)。结论:超声不仅能对CHD胎儿心内结构畸形做出明确诊断,还能通过脑沟回及脑血流参数的测量来评估胎脑发育情况,为CHD胎儿转归提供临床依据。     

血清BNP、CK-MB、H-FABP水平早期动态检测对先心病合并肺炎患儿病情评估的临床价值

目的研究血清脑钠肽(BNP)、肌酸激酶同工酶(CK-MB)及心肌型脂肪酸结合蛋白(H-FABP)水平的早期动态检测在评估先天性心脏病(CHD)合并肺炎患儿病情中的作用。方法前瞻性选取解放军总医院第三医学中心2014年1月至2019年1月间收治的267例CHD合并肺炎患儿纳为研究组,同时将同期收治80例单纯肺炎患儿纳为对照组。检测两组患儿血清BNP、CK-MB及H-FABP水平。并根据研究组患儿是否并发心力衰竭(HF),将其分为HF组与无HF(NHF)组;根据HF严重程度,将研究组并发HF患儿分为轻、中、重度组;根据研究组并发HF患儿治疗情况,将其分为治疗前与治疗后。分别比较不同分组患儿血清BNP、CK-MB及H-FABP水平。最后绘制ROC曲线,分析以上血清物质在诊断先CHD合并肺炎患儿病情中的价值。结果研究组患儿入组时血清BNP、CK-MB及HFABP水平均显著高于对照组(P<0.05);研究组CHD合并肺炎患儿HF发生率为47.19%;HF组患儿BNP、CK-MB及H-FABP水平显著高于NHF组(P<0.05);随着心力衰竭程度的加重,HF组患儿血清BNP、CK-MB及H-FABP水平呈依次上升趋势,轻度组、中度组及重度组间差异显著(P<0.05);HF组患儿治疗后,其血清BNP、CK-MB及H-FABP水平均较入组时显著降低(P<0.05);绘制ROC曲线提示,血清BNP、CK-MB及H-FABP单独应用于CHD合并肺炎患儿心力衰竭中以BNP诊断效能最高[AUC=0.883,95%CI(0.838~0.919)],三者联合应用能有效提高诊断各物质单独应用的价值[AUC=0.949,95%CI(0.904~0.993)]。结论并发心衰的CHD合并肺炎患儿血清BNP、CK-MB及H-FABP浓度均明显高于无心衰者且随着心衰程度的加重,其血清BNP、CK-MB及H-FABP浓度均呈依次上升趋势绘制ROC曲线发现,各物质单独应用时,以BNP诊断HF的效能最高,而三者联合应用能有效提高CHD合并肺炎患儿并发HF的诊断价值。     

2型糖尿病合并冠心病患者血脂结果分析

目的探讨2型糖尿病(T2DM)合并冠心病(CHD)以及T2DM患者的血脂水平,为CHD的预防和控制提供参考数据。方法用酶法(COD-PAP法)检测血清总胆固醇(TC),用GPO-PAP法检测血清三酰甘油(TG),用选择性抑制法(SPD法)检测高密度脂蛋白胆固醇(HDL-C),用表面活性剂清除法(SUR法)检测低密度脂蛋白胆固醇(LDL-C),用免疫比浊法检测载脂蛋白A1(ApoA1)、载脂蛋白B(ApoB)。检测对象分为T2DM组、T2DM合并CHD组以及正常对照组,检测结果进行统计学分析。结果 T2DM合并CHD组TC、TG、LDL-C、ApoB水平明显高于T2DM组并且组间有显著性差异(P<0.05),HDL-C、ApoA1在两组间差异无统计学意义(P>0.05)。与对照组比较:T2DM合并CHD组以及T2DM组TG、TC、LDL-C、ApoB水平均明显升高并且组间均有高度显著性差异(P<0.01);HDL-C水平均低于对照组并且组间差异有统计学意义(P<0.05);T2DM组ApoA1水平低于对照组但组间差异无统计学意义(P>0.05),T2DM合并CHD组ApoA1水平低于对照组并且组间差异显著(P<0.05)。结论 T2DM合并CHD以及T2DM患者血脂水平明显异常,应加强血脂异常的预防和治疗。     

三维超声测量正常中晚期单胎妊娠胎儿产尿率

目的 应用三维超声测量正常中晚期单胎妊娠胎儿的膀胱容量以估算不同孕期胎儿的产尿率,并探讨胎儿产尿率与孕周及羊水指数之间的关系.方法 对138例正常中晚期单胎妊娠胎儿进行三维超声检查,采用三维超声体积自动测量技术,间隔5～15 min,重复2～3次测量胎儿膀胱容量并计算产尿率.结果 胎儿的产尿率随孕周增加而增加,自孕24周的12.84 ml/h升至孕42周的64.70 ml/h,二者之间有明显相关关系(r=0.900,P<0.05).胎儿的产尿率与羊水指数无明显相关关系(r=-0.199,P>0.05).结论 运用三维超声体积自动测量技术测量正常中晚期单胎妊娠胎儿的膀胱容量变化可估算胎儿的产尿率,并可了解胎儿肾功能状态及宫内安危情况.     

Impact of congenital heart disease on cerebrovascular blood flow dynamics in the fetus.

OBJECTIVES: Neurological abnormalities are present in some children after repair of congenital heart disease (CHD). Recently, structural brain abnormalities have been identified in infants prior to cardiac surgery. By altering in utero blood flow patterns, the type of CHD may impact upon cerebrovascular flow dynamics prior to birth. We sought to determine whether left- and right-sided obstructive congenital heart lesions modify cerebrovascular flow dynamics in the fetus. METHODS: Pulsed Doppler was used to measure blood flow velocities in the umbilical (UA) and middle cerebral (MCA) arteries in 172 fetuses from 20 to 39 weeks' gestational age referred for fetal echocardiography. Pulsatility index (PI), an indicator of downstream vascular resistance, was determined by (peak systolic velocity--end-diastolic velocity)/mean velocity. RESULTS: Fetuses with hypoplastic left heart syndrome (HLHS; n = 28) had decreased MCA-PI (P = 0.009) compared to normal fetuses (n = 114). Fetuses with right-sided obstructive lesions (RSOL; n = 17) had increased MCA-PI (P = 0.001) when compared to fetuses with HLHS. The UA-PI was elevated in fetuses with RSOLs (P = 0.045). CONCLUSIONS: Cerebrovascular resistance is lower than normal in fetuses with HLHS, a condition in which cerebral perfusion occurs retrograde via the ductus arteriosus. Fetuses with RSOL had significantly higher cerebrovascular resistance compared to fetuses with HLHS. The type of CHD impacts upon fetal cerebrovascular blood flow distribution and this may have implications for later development of neurological sequelae.     

Cardiac axis in fetuses with abdominal wall defects.

OBJECTIVES: To investigate whether fetal cardiac axis is affected by the presence of an abdominal wall defect (AWD) independent of congenital heart disease (CHD). METHODS: Video ultrasound records from fetuses with AWDs identified from 1991-2004 were reviewed. Still images of the fetal cardiac four-chamber view were digitized and two independent examiners measured the cardiac axis. A cardiac axis of >65 degrees or <25 degrees was considered abnormal. Maternal charts were reviewed for fetal echocardiogram results and neonatal charts were reviewed for confirmation of CHD and type of AWD. RESULTS: Of 17 fetuses with omphalocele and 42 fetuses with gastroschisis, 16 (27%) fetuses had an abnormal cardiac axis, while only seven (12%) had CHD. Fifty-nine percent of fetuses with omphalocele had an abnormal cardiac axis and 35% had CHD. Fourteen percent of fetuses with gastroschisis had an abnormal cardiac axis and 2% had CHD. Of 43 fetuses with a normal cardiac axis, only one had CHD. CONCLUSIONS: Fetal cardiac axis is often affected by the presence of an AWD independent of CHD. A normal cardiac axis in fetuses with AWDs is an accurate predictor of the absence of CHD, the negative predictive value being 97.7%.     

Detection rate of early fetal echocardiography and in utero development of congenital heart defects.

OBJECTIVE: The purpose of this study was to evaluate the detection rate of early fetal echocardiography and the in utero development of congenital heart defects (CHD). METHODS: Cases were selected from all singleton pregnancies between 1997 and 2003 in which detailed fetal 2-dimensional and color-coded Doppler echocardiography was performed in our prenatal unit between 11 weeks' and 13 weeks 6 days' gestation; 2165 cases with complete outcome parameters were analyzed. RESULTS: During this study period, CHD were diagnosed in 46 fetuses. Between 11 and 13 weeks' gestation, 29 CHD were diagnosed (11 weeks, 9 cases; 12 weeks, 8 cases; and 13 weeks, 12 cases); 9 CHD were found in the second trimester and 2 in the third trimester. The in utero detection rate of fetal echocardiography was 86.96% (n = 40). Six additional CHD (13.04%) were detected postnatally. The spectrum of detected CHD changed with advancing gestational age and was different from the postnatal detected heart defects. CONCLUSIONS: Early fetal echocardiography is feasible and allows the detection of most CHD. Congenital heart defects vary in appearance at different stages of pregnancy and may evolve in utero with advancing gestational age. Therefore, early fetal echocardiography should always be followed by echocardiography at mid gestation.     

胎儿超声心动图在胎儿先天性心脏病产前诊断中的临床价值

目的 探讨胎儿超声心动图在产前诊断胎儿先天性心脏病的临床意义。方法 选择妊娠＞16周,分娩前有高危倾向的孕妇310例行胎儿超声心动图检查。检查中着重观察胎儿腹部切面、胎儿四腔心切面、胎儿左右室流出道长轴或大动脉短轴切面、胎儿主动脉弓长轴切面。结果 共发现9例先天性心脏病胎儿,其中复杂先天性心脏病7例、单纯室间隔缺损1例、1例出生前未确诊,出生后诊断为法洛四联症。敏感性82％,特异性100％。结论 胎儿超声心动图早期诊断胎儿畸形,评价胎儿心功能的有用工具。其诊断的准确性受孕妇体形、胎儿体位以及检查者的经验积累等多方面因素的影响。     

Measurement of fetal urine production by three-dimensional ultrasonography in normal pregnancy.

OBJECTIVES: Measurement of fetal urine production may provide a means of evaluating amniotic fluid volume, which is difficult to measure directly, and predicting fetal hypoxia. Although there have been some reports on fetal urine production, most of these have used two-dimensional (2D) ultrasonography to measure bladder volume. Three-dimensional (3D) ultrasonography is, however, known to be superior to 2D ultrasonography in some organ volume measurements. Thus, we undertook this study to measure bladder volumes using 3D ultrasonography and to establish a nomogram of fetal urine production rate (UPR) according to gestational age (GA). METHODS: One hundred and fifty-four women with a normal singleton pregnancy at 24 to 40 weeks' gestation were enrolled in this cross-sectional study. The women had no medical or obstetric complications affecting amniotic fluid volume. Fetal bladder volume was measured using 3D ultrasound imaging and Virtual Organ Computer-aided AnaLysis (VOCAL) with a rotational angle of 30 degrees and manual surface tracing technique. Bladder volume was measured two or three times within a 5-10-min interval and fetal UPR was calculated from serial measurements. When measurements were performed more than twice, we used the mean rate of calculated UPRs. UPR was then plotted against GA to establish the nomogram. RESULTS: Fetal UPR increased with GA from a median value of 7.3 mL/h at 24 weeks' gestation to 71.4 mL/h at term, and could be calculated from GA using the formula: Ln(UPR) = - 6.29582 + (0.43924 x GA) + (0.000432 x GA2), r2 = 0.63, P = 0.0046. Growth percentiles of UPR according to age are presented. CONCLUSIONS: Fetal UPR can be easily measured by 3D ultrasound assessment of bladder volume. This modality may be a promising alternative to conventional methods of amniotic fluid volume measurement such as amniotic fluid index and single deepest pocket, and might be an alternative option for predicting fetal hypoxia.     

Foramen ovale size in the normal and abnormal human fetal heart: an indicator of transatrial flow physiology.

We used fetal echocardiography to measure the sizes of the foramen ovale and atrial septum in 80 human fetuses from 17.5 to 38 weeks gestation. Forty-six fetuses had normal cardiac anatomy, 19 had left heart obstructive lesions, and 15 had right heart obstructive lesions. Pulsed and color flow Doppler studies were incorporated when available. We found that normal fetuses had a foramen ovale/atrial septum size ratio of 0.33 +/- 0.04 (mean +/- SD). In all (52%) fetuses in which it was available, pulsed Doppler study revealed bidirectional, but predominantly right-to-left, flow through the foramen ovale. Fetuses with left heart obstructive lesions had a foramen ovale/atrial septum size ratio smaller than normal (0.28 +/- 0.05; p < 0.001). Seven of nine fetuses with left heart obstructive lesions who had color Doppler studies demonstrated reversal of the normal flow pattern, exhibiting unidirectional left-to-right transforamenal flow. Those with right heart obstructive lesions had a larger than normal foramen ovale/atrial septum size ratio (0.47 +/- 0.04; p < 0.001). Nine fetuses with right heart obstructive lesions had color Doppler studies which demonstrated almost exclusive right-to-left transforamenal flow. We conclude that foramen ovale/atrial septum size ratio and Doppler interrogation of transatrial flow are helpful adjuncts in determining the presence of congenital heart disease in utero. In addition, early detection of abnormal foramen ovale/atrial septum size ratio may predict whether left or right ventricular development will be impaired throughout gestation, even before gross disparity of ventricular size is apparent.     

Three-dimensional (3D) and 4D color Doppler fetal echocardiography using spatio-temporal image correlation (STIC).

OBJECTIVE: Color Doppler echocardiography is used to visualize three transverse planes: the four-chamber, five-chamber, and three vessels and trachea views. Color Doppler spatio-temporal image correlation (STIC) is a new three-dimensional (3D) technique allowing the acquisition of a volume of data from the fetal heart that is displayed as a cineloop of a single cardiac cycle. The aim of the study was to examine the potential of color Doppler STIC to evaluate normal and abnormal fetal hearts. METHODS: This prospective study included 35 normal fetuses and 27 fetuses with congenital heart defects (CHD) examined between 18 and 35 weeks of gestation. Volume acquisition was achieved by initiating the image capture sequence from the transverse four-chamber view. Volumes were stored for later offline evaluation using a personal computer-based workstation in a multiplanar mode and as spatial volume rendering. RESULTS: Successful acquisition was possible in all 62 cases. The three planes could be demonstrated in 31/35 healthy fetuses and in 24/27 fetuses with CHD. Spatial volume rendering was attempted in 18 fetuses with CHD. In the four normal fetuses with inadequate visualization using color Doppler STIC, the region of interest was perpendicular to the ultrasound beam. In two fetuses with CHD inadequate visualization was related to an enlarged heart in late gestation, in which the entire cardiac volume could not be acquired. The third case was an 18-week fetus with complex CHD and transposed great vessels in which artifacts were related to confluent color signals as a result of low resolution in the reconstructed plane. CONCLUSIONS: STIC in combination with color Doppler ultrasound is a promising new tool for multiplanar and 3D/4D rendering of the fetal heart. Limitations may be found later in gestation in fetuses with large hearts and early in gestation as a result of low discrimination of signals. In addition, insonation perpendicular to the structure of interest does not image color Doppler signals and should be avoided during acquisition.