Intestinal Atresias


The incidence of fetal bowel obstruction is about 1:2000 pregnancies.


The diagnosis of fetal bowel obstruction is usually made when dilated bowel loops are noted on ultrasound examination done either routinely or as part of the investigation for fetal polyhydramnios (abnormally increased amount of amniotic fluid). Other findings in ultrasound that may suggest the presence of bowel obstruction include:

  • Polyhydramnios – one of the mechanisms that control the amount of the amniotic fluid surrounding the fetus is the normal process of swallowing of the fluid by the fetus. Once the fetus cannot swallow the fluid to bowel obstruction, the fluid accumulates in the uterine cavity, resulting in polyhydramnios. The higher the obstruction is, the more likely it will result in polyhydramnios.
  • Echogenic / bright bowel
  • Free fluid in the fetal abdominal cavity (ascites) – the result of perforation of the bowel wall due to increased in the pressure inside the bowel in cases of long-standing obstruction

 Association / etiology

Fetal bowel obstruction may be either an isolated finding, or may be associated with or the result of several conditions including Genetic disorders – including chromosomal disorders, cystic fibrosis or other genetics diseases

  • Fetal structural abnormalities
  • Fetal infections (e.g., Cytomegalovirus)


The site of bowel obstruction can occur at any point along the gastrointestinal tract. In many cases the exact type of bowel obstruction cannot be accurately determined during fetal life and the final diagnosis is made only following delivery.

The main causes of bowel obstruction are described in the table below according to the site of obstruction:






Esophageal atresia  1:5000
  • Obstruction at the level of the esophagus.
  • Difficult diagnosis during fetal life.
  • In about 90% there is a connection with the trachea
Structural anomalies:- ~60% – VACTREL (vertebrae, anal atresia, cardiac, TEF, Renal, limb/radial)

Chromosomal disorders  5-10%

Mortality  – ~20%, depends on associated anomalies

Morbidity – dysphagia

Pyloric atresia Rare
  • Obstruction at the outlet of the stomach.

Signs include markedly enlarged stomach, and polyhydramnios

May be associated with a skin disorder named Epidemyolysis bullosa  in up to 30-40% of cases ExcellentManagement by laparoscopoic pyloroplasty soon after delivery.
Duodenal atresia 1:5000
  • Obstruction in the part of the small bowel immediately continuous with the stomach called duodenum.
  • The classic sign in ultrasound is the “Double Bubble”, reflecting the presence of a second bubble near the stomach that results  from the dilatation of the segment of the duodenum between the site of obstruction and the stomach.
Structural anomalies – 70% (GI, cardiac)Trisomy 21 – in ~30% of cases Depends on the presence of associated anomalies
Small bowel atresia 1:10,000

  • Obstruction due to abnormal development of a segment of bowel anywhere along the small bowel.
  • Some cases have been suggested to be due to vascular problem with the limited blood supply to a certain segment of bowel leading to mal-development of that segment and obstruction of the bowel at this site.
  • Signs include dilated bowel loops, polyhydramnios, , ascites, calcifications
Structural anomalies -cardiac, malrotation, neural tube defects, vertebra – especially if involves the proximal (first part) of small bowel

Chromosomal abnormalities – uncommon (<1%), especially if involves the distal (second part) of small bowel

Excellent if isolated
Meconium ileus 1:3000
  • Obstruction of the small bowel by unusually thick meconium (fetal stool)
  • Seen in 15-20% of fetuses affected by Cystic Fibrosis
  • Signs include bright (hyperechogenic) bowel, bowel dilatation, as well as lack of gallbladder
Up to 95% of cases has Cystic Fibrosis
Volvulus 1:6000
  • Obstruction of the bowel due to twisting of bowel loops around each other.
  • Signs include dilatation of bowel loops, as well as twisting of the bowel loops around each other (Whirlpool sign).
Related to malrotation of the bowel. Variable. Long standing volvulus can lead to bowel ischemia and necrosis with subsequent risk of short bowel syndrome
Hirschprung disease 1:5000

M:F 4:1hprung diseasentroversial; apparently there is physiological defecation (peak 28-34w)ustra in late gestation)hort bowel

  • Malfunction of the large bowel due to lack of innervation of bowel wall, usually starting from the anus
  • May have hereditary basis in about 5% of cases, especially if involves the whole large bowel.
  • Signs is ultrasound include dilatation of the large bowel. Risk for perforation and ascites is higher than in cases of small bowel obstruction.
  • Diagnosis is confirmed by means of biopsy of bowel wall after delivery
Structural anomalies – in 10-20% of cases, including  – GI, GU, CNS, craniofacial, skin, musculoskeletal

Trisomy 21  in 3-10% of cases

Multiple endocrine neoplasia type 2A – hereditary genetic syndrome associated with increased risk for endocrine tumors

Depends on the extent of large bowel involvement, associated anomalies
Anal atresia 1:5000
  • Difficult diagnosis in fetal life.
  • The diagnosis is usually made at the time of physical examination of the newborn.
Structural anomalies:- ~60% – VACTREL association (vertebrae, anal atresia, cardiac, TEF, Renal, limb/radial)

Associated with ~50 different genetic syndromes

Chromosomal abnormalities – in 8% of cases – including trisomy 21, 18, 13

Depends on the presence of associated anomalies

Investigation in cases of fetal bowel obstruction
In cases of suspected bowel obstruction, the investigation should include the followings:

  • Detailed ultrasound aimed at:
    • Determining the site of obstruction
    • Presence of associated anomalies
    • Evidence of bowel perforation and ascites
    • Presence of polyhydramnios
  • Genetic studies
    • Amniocentesis for karyotype
    • Assessment of the parents for Cystic Fibrosis mutations
  • Testing for fetal infection – by means of maternal blood test and amniocentesis

Complications of bowel obstruction

Bowel obstruction may have several consequences, including:

  • Bowel ischemia – this can be especially seen in cases of Volvulus. Diffuse long standing ischemia may lead to significant degree of bowel necrosis. After delivery the necrotic segments of bowel are resected, and, when extensive, this may result in short-bowel syndrome.
  • Bowel perforation and meconium peritonitis – following bowel perforation, the meconium (fetal stool) may leak to the abdominal cavity and lead to irritation of abdominal tissue, eventually resulting in extensive inflammatory response and adhesions.
  • Preterm labor – in cases complicated by polyhydramnios (large amount of amniotic fluid) which leads to over-distension of the uterine wall, which may, in turn, result in premature contractions or preterm premature rupture of membranes.




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Fetal Medicine: 416-586-4800 x 7756
Fax: 416-586-3216

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Fax: 416-586-5109

Main clinic hours: Monday to Friday, 8am to 4pm

Prenatal Diagnosis & Medical Genetics

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phone: 416-586-4800 x 4523
fax numbers:
416-586-4723 or 416-586-8384

Perinatal Mental Health

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Phone: 416-586-4800 x 8325
Fax: 416-586-8596