Fetal atrioventricular septal defect

Atrio-ventricular septal defect (AVSD) is characterized by an incomplete division of the atria and ventricles, resulting in a single common valve between the atria and ventricles. This condition is commonly seen in children with Down syndrome. Typically, there are 2 big categories of AV canal (AVSD): partial AV canal and complete AV canal. Complete AV canal can further be subdivided regarding balanced and unbalanced. There may also be associated anomalies, as more complex anatomical variants (such as those with heterotaxy, total abnormal pulmonary venous connection/return, interruption of inferior vena cava with with azygos continuation, etc.). Unbalanced AV canal may present complex variations, with: outflow tract obstruction (pulmonary or systemic), the inflow(s) committed to one ventricle, the hypoplasia of one of the ventricular chambers, etc.). 

Both types of AV canal defects can result in varying degrees of blood flow mixing between the left and right sides of the heart, leading to pulmonary overcirculation (often less marked in infants with T21, as they have higher PVR), eventual signs of heart failure, and other potential complications in the long-term if not corrected (failure to thrive, pulmonary hypertension, etc.). Treatment include surgical repair of the defect, which often involves closing the septal defect and separating the common valve into two distinct valves. The repair of unbalanced AV complete is more complex and depends on the underlying anatomy.

More on post-natal atrio-ventricular septal defect here (see presentation).

Case of balanced atrio-ventricular septal defect

Fetal case of complete atrioventricular septal defect. The atrial and ventricular components with common atrioventricular orifice. There is balanced ventricles with no left or right-sided atrioventricular valvular regurgitation. No evidence of LVOT obstruction or antenatal suspicion of coarctation. Both atrioventricular valves are at the same level (in normal anatomy: tricuspid valve implanted lower than the mitral valve).

Cases by Dr Wadi Mawad - pediatric cardiologist at the Montreal Children's Hospital: Balanced, unbalanced, single-ventricle AVSD with TAPVR:

Common AV valve opening equally over 2 well developed ventricules

Unbalanced AVSD

AVSD with abnormal total pulmonary venous connection. A hint is the large separation between the descending aorta and the posterior aspect of the LA. These structures are usually in very close proximity. When they are not, TAPVC should be suspected and excluded.

AVSD with abnormal total pulmonary venous connection demonstrated by colour flow

Neonatal Guidance in anticipation of fetal balanced AVSD

This is information that I typically include in my antenatal consultations. However, this needs to be adapted to your institution and practice. It is only provided here as a matter of reference:

An atrioventricular septal defect is associated with Trisomy 21, although it may occur with other genetic conditions as well as in isolation (without any recognized genetic component). When balanced, these babies usually require a surgery around 3-6 months. Babies with concomitant trisomy 21 often have higher early pulmonary vascular resistance. As such, they have a tendency to have less pronounced or delayed signs of pulmonary overcirculation compared to their non-trisomy 21 counterpart with AVSD. Pulmonary overcirculation presents with respiratory difficulties, sometimes requiring respiratory support, as well as tachypnea, work of breathing. These infants often require caloric support and may have some failure to thrive. Many of these patients will require post-natal chronic diuretic therapy to manage their congestive heart failure. These patients will usually have a progressive pulmonary edema and heart failure as the PVR are dropping, due to increase Qp/Qs.  Patients with AVSD will be followed by cardiology throughout life, even in adulthood.


NICU team will be at delivery and baby is admitted to the NICU for especially cardiac and genetic evaluation. During the consultation with the family, we explain the functioning of the unit, the visiting policies, the support to breastfeeding and lactation. Also, during the consultation is discussed the breastfeeding practices, support and presence of lactation consult in NICU, breast pumps support, skin to skin practices, voice recording, music therapy, family rooms, potential for psychological support, support by the social services and benefits from the foundation (such as En Coeur foundation). We usually indeed discuss skin to skin policy, and the “bring a book from home” to read every day (or speak to baby every day). At the Montreal Children’s Hospital, we also have a book program for families in order to stimulate language acquisition early.


AVSD, due to the “goose-neck” deformity of the left ventricular outflow tract, is at risk of LVOT obstruction and hypoplastic arch. During fetal echocardiography, the fetal cardiologist may assess for the risk of left outflow obstruction (although it may be very challenging to completely predict prenatally). In situations where the LVOT obstruction risk is low, the baby is most commonly stable at birth and can be fed. If no breastmilk available, human milk from a bank should be considered – until at least the LVOT obstruction or hypoplastic arch is ruled out.


In terms of length of hospitalization, parents should be aware that some may require only a few days, while other may stay much longer in the NICU or hospital depending on the capacity to feed, glucose control, hypotonia, respiratory fatigue-obstruction, temperature control and need for enteral-feeding support (especially if T21 is present). Indeed, trisomy 21 may be associated on its own with other various anomalies. Information should be given during consultation about common problems (hypotonia, feeding difficulties, developmental delays, intellectual disabilities, language delays, hypothyroidism, hematological problems, requirement of special education, etc.) of infants with Trisomy 21 (if present). These patients must be followed actively by a general pediatrician. Also, infants with Trisomy 21 should be referred for early rehabilitation to maximize their development potential, with occupational therapy and physiotherapy (as part of the early intervention program). In Quebec, babies with concomitant trisomy 21 have access to rehabilitation and the earlier confirmatory genetic diagnosis allows for rapid access to resources (via social worker and occupational therapy) for OT, PT, language, etc., as well as for special access programs. Babies with T21 have lifelong health related conditions and need surveillance. She has my phone number and email for in case of future questions or clarifications.

For a fetus with balanced atrioventricular septal defect without prenatally identified outflow tract obstruction. These babies are likely to be asymptomatic at birth. Baby is admitted to NICU to have cardiac and genetic evaluations, with surgery planned around 3 to 6 months of age depending on his/her pulmonary over circulation symptoms. Typical plan includes:


For the baby:

- Regarding AVSD, delivery can be done vaginally at term unless other obstetrical concerns arise.

- At birth, presence of the neonatal resuscitation team.

- Birth occurs in a perinatal centre with pediatric/fetal cardiology expertise. In our context, we recommend delivery at the Montreal Children's Hospital due to the risk (although rare) of significant LVOT obstruction or hypoplastic arch leading to a coarctation physiology.

- No contraindications for vaginal delivery and delayed cord clamping based solely on the cardiac defect.

- Baby can be given 20 minutes with mother if stable before admission to NICU and can be introduced breastfeeding


Upon arrival to the NICU:

- If baby is stable, no peripheral IV insertion is needed. Baby may feed upon admission with breastfeeding, expressed breast milk and (if really not possible to have mom at bedside to breastfeeding) with pasteurized human milk (depending on eligibility by your institution). Please obtain support from lactation consultant and social worker (eligible for EnCoeur benefits in Quebec). Baby may need gavage if neurological/hypotonia difficulties related to feeds (or respiratory obstruction or TTN) - especially when concomittant trisomy 21.

- If signs of respiratory distress, cyanosis, IV insertion may be required.

- Cardiology and Genetic consultation after admission.

- Consider abdominal/head ultrasounds, as well as ophthalmology and audiology evaluation during NICU stay.

- Some newborn with AVSD are at risk of arch obstruction, as such, femoral pulses should be evaluated at every care and 4 limb blood pressure monitored q4hours until the first postnatal echocardiography confirms no arch obstruction.

If Trisomy 21 concomittant: 

- Evaluation by occupational therapy, and reference to early intervention/rehabilitation program (eligible with T21).

- I have provided to the family our contact information in case of further questions in the upcoming future.

- CBC in the context of T21.

- Will need regular surveillance/evaluation of T21 infants as per AAP standards (such as for hypothyroidism)

- Evaluate that the baby has no signs of intestinal obstruction, patent anus and esophagus. Please do one chest-abdo xray before feeding to make sure no signs of intestinal obstruction (ultrasound does not seem to show that, but there was some borderline high amniotic fluid)

- Will need hypoglycemia protocol (may be hypotonic and having inefficient feeding efforts)

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