Physiologic umbilical herniation occurs during the eighth week of development when the fetal midgut extends into the extraembryonic coelom, occupying the proximal segment of the umbilical cord. This herniation is associated with the development of normal bowel rotation in fetal life.

The bowel undergoes a 270° counterclockwise rotation, the first 90° of which occurs by week 10, extracoelomically at the base of the umbilicus. The remaining 180° clockwise turn occurs after the bowel returns to the abdomen. Rotation occurs around the axis of the superior mesenteric artery. Theoretically, this may occur because of the large fetal liver and kidneys and because the rapid development of midgut outgrows the abdominal cavity at this stage of development. The midgut returns to the abdominal cavity at 12 weeks of menstrual age.

Physiologic umbilical herniation should not persist beyond 12 weeks of gestation. After 12 weeks\' gestation, one must consider omphalocele as the cause of mass in the base of the umbilical cord and beyond the confines of the abdominal wall.

Physiologic midgut herniation should not exceed 7 mm in diameter and that physiologic herniation should not be apparent in fetuses with a crown-rump length greater than 44 mm.

Omphalocele

The diagnosis of omphalocele should not be made before 12 weeks gestation or a crown-rump length of 45 mm or less , unless the anterior abdominal mass is greater than 7 mm  or contains the liver or stomach .Prenatal US diagnosis of omphalocele is based on demonstration of a midline anterior abdominal wall defect, a herniated sac with visceral contents,and umbilical cord insertion at the apex of the sac.

The size of the omphalocele is best measured by using the ratio of the transverse diameter of the omphalocele to the transverse diameter of the abdomen. When the ratio of the diameter of the omphalocele to the transverse diameter of the abdomen is less than 60%, the lesion usually contains bowel and not liver

                                                           Gastroschisis

 Gastroschisis is an evisceration to the right of the umbilical chord normally inserted. It has an incidence of 1/10,000 to 1/15,000 births. It has a heterogeneous etiology, resulting in many cases from either an accident or vascular insult in the development of the right omphalomesenteric artery, what leads to necrosis of the base of the umbilical chord. The umbilical chord remains intact, medially to the defect. The defect size varies from 2 to 5 centimeters.

 
                                                    Omphalocele                            | Gastroschisis
Localization                      |  Umbilical cord wrapping               |  To the right of umbilical cord             
Membrane                       |  Yes                                                     |  No
Herniated structures      |  Intestines and/or liver                    |  Mostly intestines
Chromosomal disorders|  Frequent                                           |  Infrequent
Associative syndromes   |  Yes                                                     |  No