Siamese is an exceptional obstetric malformation, occurring once in every 50,000 to 60,000 births [1] [2] , with a perinatal mortality rate of 60%. It results from incomplete separation of the embryonic disc before the third week of pregnancy, the aetiology of which remains poorly understood. In fact, two theories explain its aetiopathogenesis: the theory of incomplete fusion of a single embryo and that of fusion between two embryos [3] . Conjoined twins are classified according to the most important site of union, with the suffix pagus meaning fixed. Several classifications have been described [4] . Prenatal diagnosis of conjoined twins was first reported by Wilson et al. [5] , who demonstrated the crucial role of ultrasound not only in diagnosis but also in establishing the degree of conjunction. Prenatal diagnosis of Siamese twins, the main aim of which is to assess the viability of the twins, offers a wide range of management options depending on the presumed prognosis. These include termination of pregnancy, continued pregnancy and delivery with subsequent separation, or even selective fetal reduction in higher-order multiple pregnancies. Despite a detailed assessment of prenatal lesions, this entity remains a real surgical challenge, as it is not always possible, not always easy, and the prognosis is uncertain, even with experienced teams. In the Central African Republic, a country with limited resources, this case of siamese poses a real management problem, as it is often diagnosed late and compromises the woman’s life. The aim of our analysis, through our clinical case and a review of the updated literature, is to study the value of early antenatal diagnosis while detailing the various difficulties encountered in the management of this type of anomaly and to insist on multidisciplinary collaboration in a tertiary hospital structure in the hope of improving the mother and newborn baby prognosis.

This was a 20-year-old parturient, 2nd gesture and 2nd parity, spontaneous pregnancy partially monitored with only three contacts; no obstetric ultrasound had been performed. She was referred to the department for retention of the last head following an initially unsuccessful unassisted home birth. Her family then took her to the local Level I maternity hospital. When the foetus could not be expelled despite attempts at obstetric manoeuvres, the parturient was referred to the maternity ward of the community university hospital for treatment. On admission, the fetus was in good general condition, BP 120/76 mmHg, pulse 105/min FR 22 cycle/min, 3 CU/10mn, all fetal limbs were at the vulva and the back was forward, while fetal heart sounds were absent. On vaginal touch, the fetal head was noted to be above the superior strait at the −4/5th level. On the basis of the above, we confirmed the referral diagnosis and sought to understand the aetiology. We carried out an obstetric ultrasound in the delivery room, which revealed two fetal cephalic poles with biparietal perimeters measuring 87 mm and 90 mm, respectively, without revealing the other fetal podalic pole or the plane of the back, which was unusual, leading us to conclude that there was a twin pregnancy malformation with probable fusion of the cephalic poles. Hence the indication for a maternal rescue caesarean section, which resulted in the laborious extraction of a stillborn Siamese twin weighing 3400 g female, followed by delivery of a single placenta and closure of the placenta section by section. Figure 1 is an image of our case.

Conjoined twins are rare, with a prevalence of between 1 in 50,000 pregnancies in utero and 1 in 250,000 live births [1] [2] . Its rarity is due to the rarity of twin pregnancies (approximately 1% to 2% of pregnancies), the rarity of monozygotism (approximately 35% of twin pregnancies), the rarity of embryo division after the 14th-day post-fertilisation or partial fusion of the two primitive lines leading to conjoined twins. Conjoined twins are generally incompatible with life, meaning that 65% of cases are stillborn, while of those born alive, 35% die within the first 24 hours [6] . Only 25% survive to an age where surgical separation can be considered [7] . The aetiopathogeny of conjoined twins has always been, and remains to this day, a subject of debate, with many hypotheses being considered and others completely abandoned:

Others are still being discussed. However, none of them has really been proven.

There are currently 2 main theories concerning the mechanism of formation of conjoined twins:

Siamese twins are one of the rarest congenital malformations and still present a major challenge in terms of antenatal and neonatal treatment. Ante-natal diagnosis is more often established in the first trimester, but in our country, with limited resources and despite low household incomes, it is sometimes delayed and only observed at the time of delivery and in the face of the various obstetric complications that ensue. Incorporating compulsory obstetric ultrasound into the criteria for the holistic management of pregnant women could avoid the surprises and complications associated with the dystocic delivery of Siamese twins, in addition to training providers in the obstetric sector.

The patient’s informed consent had been obtained.