An acardiac fetus is a rare malformation specific to multiple monozygotic pregnancies. This involves a fetus deprived of a heart that develops under complete vascular dependence on a healthy second twin.

Its frequency is estimated to be 1/35,000 births, or 1% of monozygotic twin pregnancies(1,2). Its course is constantly lethal to the affected fetus. ^{1, 2}

Currently, the contribution of Doppler ultrasound to antenatal diagnosis and monitoring of this pathology is essential. Different therapeutic methods have been proposed to preserve the prognosis of the healthy fetus. ^{3, 4}

Herein, we report a case of an acardiac fetus diagnosed in the obstetrics and gynecology department at Ibn Jazzer University Hospital.

This is the case of a 36-year-old female patient with B-positive blood type, without medical history, Gravida 3, Para 4. Her first pregnancy was carried to term without incident with delivery by cesarean section of a female baby with a birth weight of 3000 g. The second pregnancy was also carried to term with delivery by cesarean section of a polymalformed male baby, complicated with neonatal death.

The current pregnancy was well-monitored, the serologies for toxoplasmosis, hepatitis, and syphilis were negative, and the serology for rubella showed a state of long-standing immunity.

The first ultrasound was performed at 11 weeks by her gynecologist and showed a monochorionic monoamniotic twin pregnancy. The first twin had a normal morphology and cardiac activity, while the second twin had no cardiac activity ( Figure 1) Figure 1. .

At 23 weeks an ultrasound check was carried out and showed: ➢

For the First twin: A healthy female fetus with measurements coherent with the presumed age of pregnancy without stunted growth. There were no visible malformations at this age ( Figure 1).

For the second twin: The acardiac monster shows: ( Figure 2) •

Alobar holoprosencephaly with thalamic fusion and a very large single ventricle without visible hemispherical parenchyma.

The patient was referred for follow-up and management after 24 weeks.

A weekly ultrasound check was carried out, showing: a favorable evolution of the healthy twin; on the other hand, for the acardiac twin, an increase in volume with obvious polyhydramnios was observed.

A diabetes screening was done, returned pathological.

The etiological investigation was completed with EBV and CMV serology, and control of toxoplasmosis serology with a negative result.

The evolution was marked by the appearance of uterine distension (uterine height = 50 cm) with uterine contractions (the cervical length = 2.6 cm) Hence tocolytic treatment was initiated as well as fetal lung maturation at 30 weeks.

At 34 weeks + 4 days, the patient presented with significant respiratory difficulty; hence, a cesarean section was decided in collaboration with the neonatologists and gave birth to two babies: -

The first was female, weight = 2150 g, size = 44 cm, cranial perimeter = 31 cm. Her Apgar scores at the first and fifth minutes were 9 and 10, respectively.

Acardiac fetuses were first cited in 1533 by Benedetti and were described in the 19th century by Geoffroy-Saint-Hilaire. ⁵

In 1977, James estimated the incidence of acardiac fetuses at 1 in 35,000 births and 1% of monozygotic pregnancies. ⁶

A literature review of 340 cases carried out by James revealed that the complication more frequently affects monozygotic monoamniotic pregnancies than diamniotic multiple pregnancies. ⁶

The acardiac fetus results from an extreme form of twin-to-twin transfusion syndrome, described under the term “twin-reversed-arterial-perfusion-sequence”: TRAP sequence. ³

This fetus, also called the “container twin”, is perfused in a retrograde manner by a viable twin called the “pump twin”. He receives blood from the normal fetus. ⁷

The acardiac fetus is never viable, with a mortality rate of 100% intrauterine survival is only possible through the coexistence of a twin, which ensures its circulation and needs. ^{8, 9}

This pathology has been described for monozygotic, monochorionic multiple pregnancies. ^{6, 10}

Two main theories have been proposed regarding the etiology of this malformation. ⁸

The first antenatal diagnosis of the acardiac fetus by ultrasound was reported, in the literature, in 1978. ¹¹

The age of pregnancy at the time of diagnosis varies from 12 to 34 weeks; on average, the diagnosis is made at 23 weeks, the date of morphological ultrasound. ^{12, 13}

For our case, the ultrasound diagnosis was made at 23 weeks.

In the first trimester, according to Baron, diagnosis can be suspected in the presence of the following: •

A monochorionic twin pregnancy.

For Abboud, ultrasound and Doppler can guide diagnosis by showing the absence of cardiac activity, poor definition of the head and trunk, hypertrophy of soft tissues, and the existence of blood flow through the umbilical cord.

Ultrasound control 15 days after the first detection is of great diagnostic and prognostic value. It could specify the growth rate of the malformed fetus; if its dimensions have increased, the diagnosis will be strongly suspected.

In the second trimester, 30 of 35 acardiac fetuses were discovered in the second trimester. This was the case in our observation. ³

Borrell proposed diagnostic criteria in case of the absence of cardiac activity: •

Limb movements.

According to Monteaguado, the diagnosis will be made when an amorphous mass is visualized without proper movements, including cystic formations and major malformations of the spine and extremities. ¹³

As for MRI’s contribution to diagnosis, an MRI was performed in 2005 by Hata for an acardiac fetus at 24 weeks whose Doppler ultrasound did not show umbilical blood flow. This made it possible to prove the existence of this flow. It shows better sensitivity to detect even minimal flow, which exceeds the capabilities of ultrasound detection. ¹⁶

Our patient did not benefit from an MRI.

In summary, despite progress in diagnostic and therapeutic techniques, an acardiac fetus remains problematic. Ultrasonography prevails as the diagnostic technique of choice.

During pregnancy monitoring, ultrasound can detect the onset of complications affecting the fetus pump.

There is no consensus on therapeutic management. Therefore, a perfect collaboration between obstetricians and neonatologists would improve the prognosis of such pregnancies.