**2. Embryology/pathophysiology and demographics**

The embryologic developmental of the ventral body wall is reflected in its malformations. There are two types of defects, respectively, defects in the primaxial component and defects in the abaxial component. The first type of defects is often linked to neural tube-closure defects, whereas the second one manifest as limb–body wall or ventral body wall defects [2, 3]. Several hypotheses with respect to AWDS known as ventral body wall defects have been issued [4]. The embryologic origin of ectopia cordis, gastroschisis and bladder exstrophy is not yet known, but is thought to be more closely linked than that for omphalocele [5, 6]. It is considered that an abnormal closure of the ventral body wall folds during the 4th week of development is the main cause for these entities. In cases of gastroschisis, exposure to a teratogenic factor was suggested to be influential [7]. Some studies suggest that poor socioeconomic status and prenatal care, as well as teratogens (e.g. recreational drugs, salicylates, paracetamol and pseudoephedrine) may be important contributors to the development of gastroschisis [8, 9]. A combination of genetic and environmental factors was also thought to be involved in the origin of gastroschisis, and also ectopia cordis and bladder exstrophy [10–12]. Chromosomal abnormalities are diagnosed in 1.2% of infants with gastroschisis [13], whereas approximately half infants (54–57%) with omphalocele present with aneuploidies or gene disorders [14]. However, one risk factor associated with gastroschisis was identified in young maternal age, mothers under 20 years old having the highest risk [10]. The oldest embryologic hypothesis date from 1963, and state the potential teratogenic effect on the folds, which result in gastroschisis [15]. Another theory pleads for the rupture of the amniotic membrane at the base of the umbilical cord [16] or for the disruption of the omphalomesenteric (yolk-sac and vitelline) artery, resulting in infarction and necrosis at the base of the umbilicus [17]. As there is no evidence that for the amniotic rupture almost exclusively on the right side and that the omphalomesenteric artery offers blood supply to the paraumbilical region of the abdominal wall [18], the first and oldest theory may be overlooked [5]. On the other hand, omphalocele is a different entity, with a known etiology, thought to be the failure to return of the loops of bowel after the physiological herniation from the 6th to 10th week post-fertilization, when the fetal midgut extends into the extraembryonic celom, occupying the proximal segment of the umbilical cord [19]. A physiological hernia seldom exceeds 7 mm in diameter or rarely persists after 12 weeks of gestation, when the midgut returns to the abdominal cavity [20]. Other pathogenic theories include failure of complete lateral-body migration and closure of the body wall [15]. Omphalocele is more prevalent in older mothers.

The prevalence of the two most frequent entities of AWDs is reported to be for gastroschisis 3.09 per 10,000 births, with a live birth prevalence of 2.63 per 10,000 and for omphalocele 3.29 and 1.13 per 10,000, respectively [21]. The prevalence of gastroschisis has increased in the last years, whereas that of omphalocele has remained stable [22]. Regarding the prenatal diagnosis of AWDs, both omphalocele and gastroschisis are easily diagnosed at the 11–14 weeks nuchal scan. So, large studies report sensitivity for both congenital anomalies from 90 to 100% [23, 24]. In fact, reports show that 22 and 35% of the chromosomally normal cases of gastroschisis and omphalocele, respectively, were diagnosed before 14 weeks, and 50 and 30% between 14 and 23 weeks. The overall prenatal detection rate was 91.6% for gastroschisis and 83.3% for omphalocele [21].
