Katherine H Campbell, MD, MPH

Dr Campbell is Assistant Professor, Yale School of Medicine, and Medical Director, Yale Maternal-Fetal Medicine Practice, New Haven, Connecticut.

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	Dr Campbell is Assistant Professor, Yale School of Medicine, and Medical Director, Yale Maternal-Fetal Medicine Practice, New Haven, Connecticut.

	Dr Copel is Professor, Yale School of Medicine, and Vice Chair, Department of Obstetrics, Gynecology & Reproductive Sciences, Yale University, New Haven, Connecticut.

	Neither author has a conflict of interest to report in respect to the content of this article.

	A 20-year-old gravida 1 presented for a targeted anatomy ultrasound in the setting of an elevated maternal serum alpha fetoprotein (MSAFP) (7.14 MoM) obtained from routine prenatal screening. Transabdominal ultrasound revealed a full-thickness abdominal wall defect to the right of the umbilical cord insertion with herniation of abdominal contents. Free-floating loops of bowel were seen in the amniotic fluid without evidence of a covering membrane. The patient underwent serial ultrasounds to assess fetal growth and well-being. At 38 weeks’ gestation, fetal testing revealed a biophysical profile (BPP) that was 4/10 (2 points for fluid and fetal breathing). The patient was subsequently admitted to labor and delivery for repeat fetal testing and ultimately induction. She patient proceeded to have an uncomplicated vaginal delivery. At delivery, the lower half of the neonate’s body was placed in a sterile plastic bag to protect the exposed fetal bowel and promptly handed off to the waiting pediatricians. The neonate underwent a successful reduction of gastroschisis with a silastic silo and subsequent bioclosure of the defect and was discharged from the neonatal intensive care unit at 6 weeks of age.

	The term gastroschisis is derived from the Greek words “gastro,” meaning stomach, and “schism,” meaning cleft. The condition is described as a full-thickness paraumbilical defect in the abdominal wall.

 In the majority of cases, this defect lies to the right of a normally inserted umbilical cord. Abdominal wall defects are usually small (<4 cm), however, their presence invariably leads to herniation of the fetal mid gut (ileum and jejunum) (Figure 1A). 

The intestinal loops float freely in the amniotic fluid and, by definition, are not covered by peritoneal membrane (Figure 1B). Additional organs can herniate including the stomach, liver, spleen, and the genitourinary tract, but that is not common.

	Fetal assessment with ultrasound after the first trimester reveals free-floating loops of bowel with a “cauliflower-like” appearance in the setting of a normal umbilical cord insertion (Figure 2). Differentiating between gastroschisis and omphalocele is critical. By definition, omphalocele is a ventral wall defect that results in midline herniation of abdominal viscera into the base of the umbilical cord. Prior to the 1950s, gastroschisis was considered a variant of omphalocele. Now, however, the differing pathophysiologies, unique risk factors, and different perinatal outcomes of the 2 conditions are appreciated.

	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.

 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.

	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.

 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.

 However, many of the findings have shown only weak associations, including infection, nutrition, medication use, and tobacco exposure.

 Young maternal age continues to be the single strongest risk factor for fetal gastroschisis.

	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.

 Omphalocele, in contrast, is commonly associated with additional structural anomalies (60%–70%) and chromosomal abnormalities (15%–20%).

	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’ gestation

	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.

 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.

	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.

 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.

	Prior to widespread use of routine early fetal ultrasound assessment, abnormal MSAFP was often the first indication that a birth defect might be present. Elevated MSAFP is seen in virtually all cases of fetal gastroschisis and can be fairly high with median MSAFP multiples of the median (MoMs) from 7.0–9.4 MoMs, which are higher than seen with fetal omphalocele (median MSAFP 4.2 MoMs).

	Most cases of gastroschisis are diagnosed by ultrasound. Correct identification of gastroschisis has improved as technological advances have improved the clarity of ultrasound images and interpretation skills have developed. Older population studies show detection rates of approximately 85%, while newer population studies show rates of approximately 97.5%.

	Transabdominal ultrasound assessment reveals loops of fetal bowel in the amniotic cavity which are free-floating and not covered by a membrane. Closer examination of the umbilical cord insertion reveals a normally inserted umbilical cord with a small abdominal wall defect virtually always located to the right of the cord insertion. In contrast, omphalocele presents as a smooth, rounded mass containing abdominal contents. The mass is centrally located at the level of the umbilical cord insertion disrupting the normal cord insertion anatomy and the umbilical vessels can be seen coursing across the surface of the mass. Often, gastroschisis is described as having a cauliflower-like appearance, due to the presence of amniotic fluid between bowel loops creating acoustic interfaces at near and fall bowel walls.

	Gastroschisis may be seen on ultrasound after resolution of physiologic gut herniation by 12 weeks’ gestation.

 The main differential diagnosis at that time includes other abdominal wall defects (omphalocele, ectopia cordis, Pentalogy of Cantrell), amniotic bands and body stalk abnormalities, bladder extrophy, and umbilical cord cysts. Due to the association between fetal anomalies (structural and chromosomal) and omphalocele, early differentiation between omphalocele and gastroschisis is critical to provide correct antepartum counseling to a patient. Although risk of additional birth defects and chromosomal abnormalities is low, associated gastrointestinal abnormalities are more common in gastroschisis.

	Amniotic fluid is an irritant to the sensitive intestinal tissue and prolonged exposure of the bowel to amniotic fluid induces inflammation, bowel wall edema, and abnormal motility (hypoperistalsis). In fact, extra-abdominal bowel dilation (defined as diameter greater than 10 mm) is a common finding in gastroschisis, and since the 1980s, dilation of extra-abdominal bowel has been examined as a marker for possible poor postnatal prognosis. A retrospective review of 191 cases of gastroschisis revealed that 45% had extra-abdominal bowel dilation, but no association with adverse neonatal outcome.

 In addition, a systematic review of 10 observational studies concluded that fetuses with isolated gastroschisis and extra-abdominal bowel dilation are not at increased risk of adverse perinatal outcome compared with fetuses without dilation.

 Due to the current lack of association between antenatal appearance of extra-abdominal bowel and neonatal outcome, delivery planning should not be based on prenatal assessment of extra-abdominal fetal bowel.

	While extra-abdominal bowel dilation is common and does not appear to be significantly associated with postnatal prognosis, it is important to note that there is a significant association between gastroschisis and other gastrointestinal abnormalities. A systematic review and analysis found a 17% risk of gastrointestinal complications including atresia, stenosis volvulus, perforation, or necrosis.

 In utero bowel obstruction (mechanical or anatomical) may be suspected when progressive intraabdominal dilation of the stomach and intestines is appreciated. Polyhydramnios may serve as a marker for intestinal obstruction and be a risk factor for a more complicated postnatal course.

 The presence of additional gastrointestinal abnormalities can affect the postnatal course by increasing neonatal morbidity and mortality and prolonging postnatal recovery.

	Fetal growth restriction is more common in fetuses with gastroschisis. In part, this is due to the abnormal size of the fetal abdominal circumference (AC). However, even when controlling for the abnormal fetal AC, fetal growth restriction is more common in fetuses with gastroschisis. Additional ultrasound findings can include oligohydramios and abnormal fetal testing.

	Significant variability exists in antepartum management of pregnancies complicated by fetal gastroschisis. This is due, in part, to the lack of high-quality studies that could guide uniform clinical practice.

 Given the prevalence of early ultrasound assessment in the first trimester, early diagnosis of gastroschisis is possible.

	Both detailed fetal anatomical survey and fetal echocardiogram in the second trimester are indicated when gastroschisis is identified. A thorough search for additional structural abnormalities will allow for optimal patient counseling and delivery planning. Due to the low association between gastroschisis and chromosomal abnormalities, invasive testing has not been routinely advocated. However, presence of additional anomalies should prompt further consideration for invasive genetic testing. Prenatal chromosomal microarray will identify chromosomal aneuploidy, large changes in the structures of the chromosomes as well as submicroscopic abnormalities that are not detected by karyotype analysis alone. Data on the yield of microarray in isolated gastroschisis remain limited.

	Given the association between gastroschisis and fetal growth restriction (25%), spontaneous preterm birth (25%), and stillbirth (5%), serial ultrasound evaluation of fetal growth is warranted.

 Earlier gestational age at delivery has been associated with worse perinatal outcome,

 so optimal delivery planning is critical in cases of threatened preterm labor, including consideration for steroid administration to accelerate fetal maturity.

	Assessment of fetal bowel for dilation and wall thickening has been commonly advocated and performed because of the possibility of adverse outcome in the setting of extra-abdominal bowel dilation; however, a systematic review did not find significant association between dilated extra-abdominal bowel and adverse perinatal outcome.

 In contrast, intraabdominal bowel dilation has been associated with postnatal diagnosis of bowel atresia and more complicated repair.

 It is important to note that existing data conflict on the implications of both extra- and intra-abdominal bowel dilation and the association with perinatal outcome. Additional well-designed studies are needed in this area.

	Antenatal testing recommendations are mainly based on expert opinion and retrospective studies, given the association of gastroschisis with stillbirth.

 A suggested algorithm is to begin antenatal monitoring with nonstress test and amniotic fluid volume assessment or BPP at 32–36 weeks’ gestation, with earlier initiation of testing for more complicated cases (eg, in the presence of fetal growth restriction or amniotic fluid volume abnormalities).

	There is no single delivery management algorithm, and due to the association of gastroschisis with stillbirth, earlier delivery has been advocated.

 A retrospective cohort study that included 860 cases of gastroschisis from a reference population of more than 2 million singleton pregnancies found that risk of stillbirth may be minimized with delivery as early as 37 weeks’ gestation.

 In settings of normal fetal growth and fetal testing, the delivery plan can be made on a case-by-case basis, but due to the increased risk of stillbirth with advancing gestational age, fetuses with gastroschisis should undergo delivery planning by 39 weeks’ gestation. Although newer literature may support elective delivery planning prior to 39 weeks’ gestation, this is not currently standard of care and delivery prior to 39 weeks should be reserved for obstetrical indication.

	The recommended mode of delivery is vaginal, with cesarean delivery reserved for obstetrical indication as there is no evidence that cesarean delivery improves the outcome in uncompromised gastroschisis. Use of this obstetrical management algorithm is increasing, as seen in a recent population-based study that showed a rate of attempted vaginal delivery of 59.7% in 2005 and 68.8% in 2013.

	Due to the exposed fetal bowel, the neonate is at risk for insensible losses of fluid and heat (Figure 4). 

Reprinted from Obstetric Imaging (Copel JA, ed.) 2012Upon delivery, the neonate should be placed in a sterile plastic bag up to the level of the chest and handed to waiting pediatricians for assessment. The neonate should be placed on its side to avoid kinking the bowel while awaiting pediatric surgery assessment. A nasogastric tube generally is placed to decompress the stomach and intravenous access is obtained.

 One preferred method of closure for uncomplicated gastroschisis is placement of a Silastic spring-loaded silo (Figure 5).

 The defects are reduced in 1–3 days and bioclosure with umbilical cord may be used (Figure 6). If complications are suspected, exploration in the operating room is required. Approximately 17% of cases are complex due to the presence of additional gastrointestinal pathologies, and will likely require exploratory and corrective surgery prior to placement of the silo.

 Herniated bowel can also be reduced with a staged closure, if needed. The most common postnatal complications are overcoming poor mucosal function and hypoperistalsis of the fetal bowel. The neonatal mortality rate ranges from 2% to 17%, with higher rates for complex cases.

Reprinted from Obstetric Imaging (Copel JA, ed.) 2012

	Gastroschisis is a result of a full-thickness paraumbilical defect that allows herniation of free-floating fetal bowel into the amniotic cavity. Incidence of this birth defect is increasing worldwide and young maternal age at the time of pregnancy is a significant risk factor for the condition. Fetal gastroschisis is rarely associated with aneuploidy and is commonly isolated. Nearly all cases are associated with elevated MSAFP and the defect is readily diagnosed on ultrasound. Affected fetuses are at increased risk for growth restriction, preterm birth, and stillbirth. Approximately 10% of cases are associated with intestinal atresia requiring more extensive postnatal management and intervention. The atresia may or may not be diagnosed prior to birth. Recommended mode of delivery is vaginal with cesarean delivery reserved for usual obstetrical indications.

Reprinted from Obstetrical Imaging (Copel JA, ed.) 2012

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