Methods

Between July 1987 and July 2012, 53 conjoined twin pairs were identified from 25,000 referrals for fetal echocardiography to the Fetal Cardiology Unit of the Department of Obstetrics at São Paulo University Medical School. The ethics committee of Hospital das Clínicas of the University of São Paulo Medical School (São Paulo, Brazil) approved this retrospective study.

Cases were classified by obstetric ultrasound according to the most prominent site of fusion and the embryologic classification proposed by Spencer : cranium (craniopagus), head (cephalopagus), chest (thoracopagus), umbilicus (omphalopagus), lateral (parapagus), rump (pygopagus), hip (ischiopagus), and spine (rachipagus).

Specialized fetal echocardiography was performed to investigate cardiac abnormalities and assess the degree of cardiac fusion. The extent of cardiac fusion was classified according the criteria proposed by Andrews et al. : separate hearts and pericardium (group A), separate hearts and common pericardium (group B), fused atria and separated ventricles (group C), and fused atria and ventricles (group D).

Fetal echocardiographic examinations were performed and reviewed by a cardiologist (L.M.L.) whose specialty is pediatric and fetal echocardiography. Standard echocardiographic views were modified as needed to obtain accurate views of the cardiac anatomy, using transabdominal route (4-MHz to 2-MHz convex transducer, 3-MHz to 5-MHz sectorial transducer). Early fetal echocardiography was performed by the same cardiologist in two patients, referred at 16 and 14 weeks’ gestation, using a 9-MHz to 5-MHz real-time vaginal probe (cases D3 and D12). Diagnosis was made by segmental analysis of the heart, trying to define the degree of atrial and ventricular fusion, the number and morphology of the atrioventricular valves, the number and size of great arteries, and the systemic and pulmonary venous drainage when possible . Since 2009, additional tools such as Doppler tissue imaging and four-dimensional echocardiography have been incorporated to improve diagnosis. Eighteen cases underwent two-dimensional and four-dimensional echocardiography using spatiotemporal image correlation (STIC), carried out with a Voluson 730 Expert or Voluson E8 (GE, Kretztechnik, Zipf, Austria) ultrasound machine. One single best volume for each fetus was stored, and in each case we examined the acquired data in a display mode called inversion mode. This mode creates a three-dimensional rendering resembling an angiogram by removing the tissue and displaying the hollow structures as solid.

Postmortem examinations were performed with parental consent and only in twins delivered at our institution. Prenatal echocardiographic findings were compared with autopsy findings to examine the effectiveness of prenatal echocardiographic evaluation in the prediction of cardiac fusion and structural defects.

Prenatal hospital charts were reviewed. Postnatal and autopsy reports were also reviewed for the patients delivered at our hospital. The following data were collected and analyzed: gestational age at diagnosis, site of fusion, type of cardiac fusion, major cardiac abnormalities, postnatal echocardiographic findings, autopsy results, and survival rate.

Results

Fifty-three pregnancies with conjoined twins were seen during the study period. According to the most prominent site of fusion, 38 pairs (71.6%) were thoracopagus, six (11.3%) parapagus, six (11.3%) omphalo-ischiopagus, two (3.7%) omphalopagus, and one (1.8%) cephalopagus. The mean gestational age at the first fetal echocardiography examination was 24.2 ± 6.0 weeks (range, 14–39 weeks), and the total number of examinations varied from one to three (mean, 1.2 ± 0.5).

Fetal Echocardiographic Findings

According to the degree of cardiac fusion, 10 cases (18.8%) were prenatally classified in group A (separate hearts), two (3.7%) in group B (pericardial fusion), two (3.7%) in group C (atrial fusion), and 39 (73.5%) in group D ( Figures 1-3 ). Autopsy results did not confirm echocardiographic classification in three sets of twins (cases A7, B1, and D39).

Types A and B of cardiac fusion. (A) Type A, four-chamber view of both separated normal hearts. Arrows indicate the pericardium of both fetuses. (B) Type B, separated hearts and common pericardium. Arrows indicate the same pericardial space for both hearts. Ventricles are seen side by side in two-chamber position. F1 , Fetus 1; F2 , fetus 2.

Type C of cardiac fusion. (A) The right and left panels are identical images, except for display of the color Doppler in the right panel. Fused atria (A) at the coronary sinus level is seen ( white arrows ). This long coronary sinus connects one heart with double-outlet right ventricle (fetus 1 [F1]) to a rudimentary chamber without ventricular mass (fetus 2 [F2]). (B) Autopsy confirmation of the long coronary sinus connecting both hearts ( black arrow ). The rudimentary chamber (without ventricular or outlet arteries) resembles an atrium chamber (F2). L , Lung; S , spine (twins C2).

Type D of cardiac fusion. (A) Extensive cardiac conjunction with fused atria (A) and four ventricles, two with left morphology (LV) and two hypoplastic with right morphology (RV). (B) Autopsy shows one left ventricle in the center and two hypoplastic right ventricles on each side. Normal aortas (AO) are also seen. (C) Thoracopagus twins (twins D1). F1 , Fetus 1; F2 , fetus 2.

Fetal intracardiac defects were diagnosed in 47 sets of twins (88.6%). In 10 (18.8%), only one fetus was affected, and in 37 (69.8%), both fetuses were affected. Therefore, antenatal assessment demonstrated intracardiac malformations in 84 fetuses (79.2%). Considering the confirmed group type by autopsy, all sets of twins in group D had associated cardiac defects in both fetuses, and all but one were affected in group C, whereas this was observed in only 22.2% of fetuses (four of 18) in group A. Echocardiographic details are presented in Table 1 .

Table 1

Echocardiographic details of 53 cases of conjoined twins

Group	Twin	Type	Major cardiac defects		Autopsy results		Outcome
			Fetus 1	Fetus 2	Group agreement	Additional findings
A	A1	Omphalo-ischiopagus	Normal	AVSD	—	—	TOP
	A2	Omphalopagus	Normal	VSD + TGA	Yes	No	F1 alive/F2 inf D
	A3	Omphalo-ischiopagus	Normal	Normal	—	—	Both alive
	A4	Omphalo-ischiopagus	Normal	Normal	—	—	Both alive
	A5	Parapagus dicephalus	Normal	TAtr IIC + CoA	Yes	No	NND F1/F2
	A6	Omphalopagus	Normal	Normal	Yes	No	F1 NND/F2 alive
	A7 ∗	Parapagus	Normal	Normal	No	Group B	NND F1/F2
	A8	Omphalo-ischiopagus	Normal	Normal	—	—	FD F1/F2
	A9	Omphalo-ischiopagus	Normal	Severe TV dysplasia	—	—	NND F1/F2
	A10	Omphalo-ischiopagus	Normal	Normal	—	—	Both alive
B	B1 ∗	Thoracopagus	Large-inlet VSD	TAtr IIB	No	Group C	Inf D F1/F2
	B2	Parapagus dicephalus	Normal	Patr/PA not seen	Yes	F2 normal PA	NND F1/F2
C	C1	Thoracopagus	Normal	DILV + straddling TV + small RV	Yes	No	Inf D F1/F2
	C2	Thoracopagus	DORV + VSD	Single chamber without outlet	Yes	No	NND F1/F2
D	D1	Thoracopagus	TAtr IA	AT IIB	Yes	No	NND F1/F2
	D2	Thoracopagus	Shared single complex cardiac mass	Shared single complex cardiac mass	—	—	FD F1/F2
	D3	Thoracopagus	RV hypopl + VSD	RV hypopl + AVSD + AAtr	Yes	No	FD F1/F2
	D4	Thoracopagus	DORV	VSD	—	—	NND F1/F2
	D5	Thoracopagus	AVSD + small RV	AVSD + small RV	—	—	NND F1/F2
	D6	Thoracopagus	TAtr IB	TAtr IB	—	—	NND F1/F2
	D7	Thoracopagus	TAtr IB	TAtr IIA	Yes	No	Inf D F1/F2
	D8	Thoracopagus	PAtr + AVSD	TGA + AVSD	Yes	F1 normal PA	TOP
	D9	Thoracopagus	AVSD + single “aorta” for both fetuses (1A + 1V)	AVSD + single “aorta” for both fetuses (1A + 1V)	Yes	Common arterial trunk	TOP
	D10	Thoracopagus	SV + PS	TGA + PS + straddling TV	—	—	TOP
	D11	Thoracopagus	RV hypopl + VSD	RV hypopl + AVSD + PS	Yes	No	TOP
	D12	Thoracopagus	PAtr + shared single complex cardiac mass	PAtr + shared single complex cardiac mass	Yes	No	TOP
	D13	Thoracopagus	DORV	TGA + small RV and LV	Yes	No	TOP
	D14	Thoracopagus	Shared DOSV + one AV valve	Shared DOSV + one AV valve	—	—	NND F1/F2
	D15	Thoracopagus	Shared single complex cardiac mass	PA + shared single complex cardiac mass	—	—	NND F1/F2
	D16	Thoracopagus	RV hypopl + VSD	PAtr	—	—	Inf D F1/F2
	D17	Thoracopagus	VSD	SV	—	—	TOP
	D18	Thoracopagus	Shared single complex cardiac mass	Shared single complex cardiac mass	—	—	NND F1/F2
	D19	Parapagus	Normal cardiac connection with malposition	RV hypopl	Yes	No	TOP
	D20	Thoracopagus	DOSV + shared single complex cardiac mass	Great arteries not seen + shared single complex cardiac mass	Yes	F1 and F2 both with DOSV, normal PA	NND F1/F2
	D21	Cephalopagus	Patr + shared single complex cardiac mass	Patr + shared single complex cardiac mass	—	—	NND F1/F2
	D22	Thoracopagus	RV hypopl + PAtr	DORV + PS	Yes	No	TOP
	D23	Thoracopagus	Normal cardiac connection	SV + Patr/PA not seen	Yes	F2 normal PA	TOP
	D24	Thoracopagus	Large VSD + PAtr	VSD + RV hypopl + PAtr	Yes	No	TOP
	D25	Thoracopagus	Shared single complex cardiac mass (2A + 2V for both)	Shared single complex cardiac mass (2A + 2V for both)	Yes	Another atrium and hypopl V	NND F1/F2
	D26	Thoracopagus	PS + shared single complex cardiac mass	PS + shared single complex cardiac mass	Yes	No	TOP
	D27	Thoracopagus	Shared single complex cardiac mass + single arterial trunk	Shared single complex cardiac mass with single arterial trunk	Yes	No	NND F1/F2
	D28	Parapagus	RV hypopl + PS	DORV + PS	Yes	No	NND F1/F2
	D29	Thoracopagus	TAtr IC	RV hypopl	—	—	NND F1/F2
	D30	Thoracopagus	Normal cardiac connection	AVSD + RV hypopl	Yes	No	NND F1/F2
	D31	Thoracopagus	RV hypopl + VSD	TGA + VSD	Yes	No	TOP
	D32	Thoracopagus	TAtr 1A	DOSV + PS	Yes	No	NND F1/F2
	D33	Thoracopagus	SV + PS	DORV + PS	Yes	No	TOP
	D34	Thoracopagus	RV hypopl + PS	DORV + AVSD + PS	Yes	No	NND F1/F2
	D35	Thoracopagus	Normal cardiac connection	SV + AP	Yes	No	NND F1/F2
	D36	Thoracopagus	SV + RV hypopl + AP	DOSV	Yes	No	NND F1/F2
	D37	Thoracopagus	SV + EP	SV + AP	Yes	No	TOP
	D38	Thoracopagus	SV + AP	DOSV + EP	Yes	No	TOP
	D39 ∗	Thoracopagus	VSD	DORV + hypoplastic LV	No	Group C	Inf D F1/F2

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