Epidemiology and risk factors
Worldwide, incidence of gastroschisis has increased over the past 2–3 decades for reasons that are not well understood. Recent data from the Centers for Disease Control and Prevention have shown a 30% increase in incidence in US cases from 3.6 to 4.9 per 10,000 live births when comparing 1995–2005 with 2006–2012.2 In a multinational study that examined 25 birth defect registries, a significant temporal increase in gastroschisis incidence was also observed, while no similar trend was seen for 36 other malformations examined.3
Young maternal age and low maternal body mass index have long been recognized as risk factors for gastroschisis, with rates as much as 7-fold higher in women younger than age 20.2 Due to the temporal trend of increasing disease incidence combined with these risk factors, epidemiologists have proposed various environmental factors as possible links to the underlying etiology.4 However, many of the findings have shown only weak associations, including infection, nutrition, medication use, and tobacco exposure.5,6 Young maternal age continues to be the single strongest risk factor for fetal gastroschisis.2
As opposed to omphalocele, gastroschisis is less commonly associated with chromosomal abnormalities or additional birth defects. In an international population-based study, 14% of gastroschisis cases were associated with other birth defects, central nervous system anomalies being the most common, and 1.2% of gastroschisis cases were associated with chromosomal anomalies.7 Omphalocele, in contrast, is commonly associated with additional structural anomalies (60%–70%) and chromosomal abnormalities (15%–20%).8
Understanding the development of gastroschisis requires appreciation of normal embryonic development of the midgut, abdominal wall, and umbilical cord. As the embryo develops, the ventral body wall closes by 7 weeks’ gestation (35 days post conception). At that time, midgut growth is rapid and the expanding intestines herniate into the umbilical cord soon after abdominal wall closure. The midgut subsequently returns to the abdominal cavity by 11–12 weeks’ gestation9 (Figure 3a, 3b).
Several hypotheses involve mechanisms that could lead to the development of fetal gastroschisis, all of which include defective formation (malformation) or disruption of the body wall. A well-known hypothesis involves infarction and necrosis of the body wall near the base of the umbilical cord due to disruption of the right omphalomesenteric (vitelline or yolk sac) artery.10,11 The vascular pathogenesis proposal prompted research into the culpability of various vasoactive substances including cocaine, tobacco, and common over-the-counter decongestants. However, no consistent association has been shown between early pregnancy exposure to these substances and subsequent development of gastroschisis.5,6
Another hypothesis proposes failure of abdominal body folding impeding the merging of the yolk sac with the body stalk. With embryonic maturation, the intestinal loop attached to the vitelline duct herniates through the defect and into the amniotic cavity instead of undergoing the anticipated transient physiological gut herniation into the umbilical cord.12 A third mechanism proposes that the yolk sac and related vitelline structures fail to be incorporated into the umbilical stalk. This failure leads to persistence of the vitelline duct and yolk sac outside the main body stalk and abdominal wall as the abdominal folds close normally. In this scenario, the developing midgut has 2 areas of egress at the time of physiologic gut herniation, leading to abnormal herniation of the expanding midgut into the vitelline duct and amniotic cavity.10