The sac, which is formed from an outpouching of peritoneum, protrudes in the midline, through the umbilicus (navel).

It is normal for the intestines to protrude from the abdomen, into the umbilical cord, until about the tenth week of pregnancy, after which they return to inside the fetal abdomen.

The omphalocele can be mild, with only a small loop of intestines present outside the abdomen, or severe, containing most of the abdominal organs. In severe cases surgical treatment is made more difficult because the infant's abdomen is abnormally small, having had no need to expand to accommodate the developing organs.

Larger omphalocele are associated with a higher risk of cardiac defects.

Caused by malrotation of the bowels while returning to the abdomen during development. Some cases of omphalocele are believed to be due to an underlying genetic disorder, such as Edward's syndrome (trisomy 18) or Patau syndrome (trisomy 13).

Beckwith–Wiedemann syndrome is also associated with omphaloceles.

There are no signs during pregnancy. About sixty percent of infants with gastroschisis are born prematurely. At birth, the baby will have a relatively small (<4 cm) hole in the abdominal wall, usually just to the right of the belly button. Some of the intestines are usually outside the body, passing through this opening. In rare circumstances, the liver and stomach may also come through the abdominal wall. After birth these organs are directly exposed to air.

Concerns that arise due to abdominal wall defects can be threatening and require immediate and intensive medical care. Some infections may persist for long periods of time and lead to serious complications, such as feeding problems, which can cause the infant to require several surgeries. Since these complications can be severe, it is recommended that parents work closely with a team of physicians throughout the duration of the treatment. After the treatment is completed, children with abdominal wall defects may need additional help. Additional services are usually necessary for with omphalocele and the associated chromosomal abnormalities and birth defects that also arise. Treatments in these cases are long-term and focus on the physical and developmental difficulties that the children will endure. The parents may find this process difficult and need assistance in dealing with the process by a service that is provided by the healthcare team.

Gastroschisis is a birth defect in which the baby's intestines extend outside of the body through a hole next to the belly button. The size of the hole is variable, and other organs including the stomach and liver may also occur outside the baby's body. Complications may include feeding problems, prematurity, intestinal atresia, and intrauterine growth retardation.

The cause is typically unknown. Rates are higher in babies born to mothers who smoke, drink alcohol, or are younger than 20 years old. Ultrasounds during pregnancy may make the diagnosis. Otherwise diagnosis occurs at birth. It differs from omphalocele in that there is no covering membrane over the intestines.

Treatment involves surgery. This typically occurs shortly after birth. In those with large defects the exposed organs may be covered with a special material and slowly moved back into the abdomen. The condition affects about 4 per 10,000 newborns. Rates of the condition appear to be increasing.

Imperforate anus is associated with an increased incidence of some other specific anomalies as well, together being called the VACTERL association:

- V – Vertebral anomalies

- A – "Anal atresia"

- C – Cardiovascular anomalies

- T – Tracheoesophageal fistula

- E – Esophageal atresia

- R – Renal (kidney) and/or radial anomalies

- L – Limb defects

Other entities associated with an imperforate anus are trisomies 18 and 21, the cat-eye syndrome (partial trisomy or tetrasomy of a maternally derived number 22 chromosome), Baller-Gerold syndrome, Currarino syndrome, caudal regression syndrome, FG syndrome, Johanson-Blizzard syndrome, McKusick-Kaufman syndrome, Pallister-Hall syndrome, short rib-polydactyly syndrome type 1, Townes-Brocks syndrome, 13q deletion syndrome, urorectal septum malformation sequence, and the OEIS complex (omphalocele, exstrophy of the cloaca, imperforate anus, spinal defects).

The syndrome has five characteristic findings:

- Omphalocele

- Anterior diaphragmatic hernia

- Sternal cleft with or without ectopia cordis

- Diaphragmatic pericardium defects (no diaphragmatic pericardium)

- Intracardiac defect: ventricular septal defect, diverticulum of the left ventricle, Tetralogy of Fallot

There are several forms of imperforate anus and anorectal malformations. The new classification is in relation of the type of associated fistula.

The classical Wingspread classification was in low and high anomalies:

- A low lesion, in which the colon remains close to the skin. In this case, there may be a stenosis (narrowing) of the anus, or the anus may be missing altogether, with the rectum ending in a blind pouch.

- A high lesion, in which the colon is higher up in the pelvis and there is a fistula connecting the rectum and the bladder, urethra or the vagina.

- A persistent cloaca (from the term cloaca, an analogous orifice in reptiles and amphibians), in which the rectum, vagina and urinary tract are joined into a single channel.

Imperforate anus is usually present along with other birth defects—spinal problems, heart problems, tracheoesophageal fistula, esophageal atresia, renal anomalies, and limb anomalies are among the possibilities.

Abdominal wall defects are a type of congenital defect that allows the stomach, the intestines, or other organs to protrude through an unusual opening that forms on the abdomen.

During the development of the fetus, many unexpected changes occur inside the womb. Specifically the stomach, intestines, or other organs begin to develop outside the fetus’ abdomen through the abnormal hole in the abdomen and, as development progresses, the abdominal wall eventually encloses these organs. In some cases of defect either the umbilical opening is too oversized or has developed improperly which allows the organs to remain outside or to squeeze through the abdominal wall.

There are two main types of abdominal wall defects that result due to the changes during development. They are omphalocele and gastroschisis. Gastroschisis develops when the abdominal wall does not completely close, and the organs are present outside of the infant’s body. Omphalocele occurs when some of the organs protrude through the muscles of the abdomen in the area surrounding the umbilical cord. Omphalocele can be either minor, with only some of the organs exposed, or severe, with most, if not all of the abdominal organs being exposed.

The causes of umbilical hernia are congenital and acquired malformation, but an apparent third cause is really a cause of a different type, a paraumbilical hernia.

Importantly, an umbilical hernia must be distinguished from a paraumbilical hernia, which occurs in adults and involves a defect in the midline near to the umbilicus, and from omphalocele.

Pentalogy of Cantrell (or thoraco-abdominal syndrome) is a rare syndrome that causes defects involving the diaphragm, abdominal wall, pericardium, heart and lower sternum.

Its prevalence is less than 1 in 1000000.

It was characterized in 1958.

A locus at Xq25-26 has been described.

Additional symptoms include:

- anencephaly (failure of major sections of the brain to form)

- encephalocele (cranial contents protrudes from the skull)

- cyclopia (the two eye cavities fuse into one)

- agnathia

- cleft palate

- arthrogryposis

- clubfeet

- holoprosencephaly

- spina bifida

- low-set ears

- pulmonary hypoplasia

- omphalocele

- gastroschisis

- cardiovascular disorders

- diaphragmatic hernias

- gastrointestinal atresia

- single umbilical artery

- renal abnormalities

- genu recurvatum

- hydramnios

Most children with BWS do not have all of these five features. In addition, some children with BWS have other findings including: nevus flammeus, prominent occiput, midface hypoplasia, hemihypertrophy, genitourinary anomalies (enlarged kidneys), cardiac anomalies, musculoskeletal abnormalities, and hearing loss. Also, some premature newborns with BWS do not have macroglossia until closer to their anticipated delivery date.

Given the variation among individuals with BWS and the lack of a simple diagnostic test, identifying BWS can be difficult. In an attempt to standardize the classification of BWS, DeBaun et al. have defined a child as having BWS if the child has been diagnosed by a physician as having BWS and if the child has at least two of the five common features associated with BWS (macroglossia, macrosomia, midline abdominal wall defects, ear creases/ear pits, neonatal hypoglycemia). Another definition presented by Elliot et al. includes the presence of either three major features (anterior abdominal wall defect, macroglossia, or prepostnatal overgrowth) or two major plus three minor findings (ear pits, nevus flammeus, neonatal hypoglycemia, nephromegaly, or hemihyperplasia).

While most children with BWS do not develop cancer, children with BWS do have a significantly increased risk of cancer. Children with BWS are most at risk during early childhood and should receive cancer screening during this time.

In general, children with BWS do very well and grow up to become adults of normal size and intelligence, usually without the syndromic features of their childhood.

The affected infant tends to be short, with a disproportionately large head. The fetal head of Infants born with iniencephaly are hyperextended while the foramen magnum is enlarged and opens through the widened pedicles. The defective neural arches directly into the upper cervical reach of the spinal canal, causing the formation of a common cavity between most of the spinal cord and the brain. The skin of the anterior chest is connected directly to the face, bypassing the formation of a neck, while the scalp is directly connected to the skin of the back. Because of this, those born with this anomaly either have a highly shortened neck or no neck at all. This causes extreme retroflexion, or backward bending, of the head in a "star-gazing" fashion. The spine is severely distorted as well along with significant shortening due to marked lordosis. The vertebrae, especially cervical, are fused together in abnormal shapes and their numbers are reduced. The spinal cord is almost always defective while the ventricular system is often dilated and the cortex is thinned. Sometimes, in the case of iniencephaly apertus, an encephalocele (sac-like protrusions of the brain through an opening in the cranium) forms.

Due to the rarity and rapid postpartum mortality of ectopia cordis, limited treatment options have been developed. Only one successful surgery has been performed as of now, and the mortality rate remains high.

The prognosis of ectopia cordis depends on classification according to three factors:

1. Location of the defect

- Cervical

- Thoracic

- Thoracoabdominal

- Abdominal

2. Extent of the cardiac displacement

3. Presence or absence of intracardiac defects

Some studies have suggested a better prognosis with surgery in cases of thoracoabdominal ectopia cordis or less severe pentalogy of Cantrell. In general, the prognosis for ectopia cordis is poor—most cases result in death shortly after birth due to infection, hypoxemia, or cardiac failure.

Abdominal wall defects are common in newborns with BWS and may require surgical treatment. These defects can range in severity from omphalocele (most serious) to umbilical hernia and diastasis recti (least serious). An "omphalocele" is a congenital malformation in which a newborn's intestines, and sometimes other abdominal organs, protrude out of the abdomen through the umbilicus. Newborns with an omphalocele typically require surgery to place the abdominal contents back into the abdomen in order to prevent serious infection or shock. An "umbilical hernia" is also a defect in which abdominal contents come through weak abdominal wall muscle at the umbilicus. In general, newborns with umbilical hernias do not require treatment because often these hernias spontaneously close by age four. If, after this time, a hernia is still present, surgery may be recommended. "Diastasis recti" is a separation of the left and right sides of the rectus abdominis muscle that are normally joined together. Children with diastasis recti usually require no treatment because the condition resolves as the child grows.

Neonatal hypoglycemia, low blood glucose in the first month of life, occurs in about half of children with BWS. Most of these hypoglycemic newborns are asymptomatic and have a normal blood glucose level within days. However, untreated persistent hypoglycemia can lead to permanent brain damage. Hypoglycemia in newborns with BWS should be managed according to standard protocols for treating neonatal hypoglycemia. Usually this hypoglycemia can easily be treated with more frequent feedings or medical doses of glucose. Rarely (<5%) children with BWS will continue to have hypoglycemia after the neonatal period and require more intensive treatment. Such children may require tube feedings, oral hyperglycemic medicines, or a partial pancreatectomy.

Macroglossia, a large tongue, is a very common (>90%) and prominent feature of BWS. Infants with BWS and macroglossia typically cannot fully close their mouth in front of their large tongue, causing it to protrude out. Macroglossia in BWS becomes less noticeable with age and often requires no treatment; but it does cause problems for some children with BWS. In severe cases, macroglossia can cause respiratory, feeding, and speech difficulties. Children with BWS and significant macroglossia should be evaluated by a craniofacial team.

The best time to perform surgery for a large tongue is not known. Some surgeons recommend performing the surgery between 3 and 6 months of age. Surgery for macroglossia involves removing a small part of the tongue so that it fits within the mouth to allow for proper jaw and tooth development.

Nevus flammeus (port-wine stain) is a flat, red birthmark caused by a capillary (small blood vessel) malformation. Children with BWS often have nevus flammeus on their forehead or the back of their neck. Nevus flammeus is benign and commonly does not require any treatment.

Hemihypertrophy (hemihyperplasia) is an abnormal asymmetry between the left and right sides of the body occurring when one part of the body grows faster than normal. Children with BWS and hemihypertrophy can have an isolated asymmetry of one body part, or they can have a difference affecting the entire one side of the body. Individuals who do not have BWS can also have hemihypertrophy. Isolated hemihypertrophy is associated with a higher risk for cancer. The types of cancer and age of the cancers are similar to children with BWS. As a result, children with hemihypertrophy should follow the general cancer screening protocol for BWS.

Hemihypertrophy can also cause various orthopedic problems, so children with significant limb hemihyperplasia should be evaluated and followed by an orthopedic surgeon.

Hemihyperplasia affecting the face can sometimes cause significant cosmetic concerns that may be addressed by a cranial facial team.

The cranial malformations are the most apparent effects of acrocephalosyndactyly. Craniosynostosis occurs, in which the cranial sutures close too soon, though the child's brain is still growing and expanding. Brachycephaly is the common pattern of growth, where the coronal sutures close prematurely, preventing the skull from expanding frontward or backward, and causing the brain to expand the skull to the sides and upwards. This results in another common characteristic, a high, prominent forehead with a flat back of the skull. Due to the premature closing of the coronal sutures, increased cranial pressure can develop, leading to mental deficiency. A flat or concave face may develop as a result of deficient growth in the mid-facial bones, leading to a conditir prognathism. Other features of acrocephalosyndactyly may include shallow bony orbits and broadly spaced eyes. Low-set ears are also a typical characteristic of branchial arch syndromes.

Common relevant features of acrocephalosyndactyly are a high-arched palate, pseudomandibular prognathism (appearing as mandibular prognathism), a narrow palate, and crowding of the teeth.

Many organ systems are affected by triploidy, but the central nervous system and skeleton are the most severely affected. Common central nervous system defects seen in triploidy include holoprosencephaly, hydrocephalus (increased amount of cerebrospinal fluid within the brain), ventriculomegaly, Arnold-Chiari malformation, agenesis of the corpus callosum, and neural tube defects. Skeletal manifestations include cleft lip/palate, hypertelorism, club foot, and syndactyly of fingers three and four. Congenital heart defects, hydronephrosis, omphalocele, and meningocele (spina bifida) are also common. Cystic hygromas occur but are uncommon. Triploid fetuses have intrauterine growth restriction beginning early in the pregnancy, as early as 12 weeks, and does not affect the head as severely as the body. Oligohydramnios, low levels of amniotic fluid, is common in triploid pregnancies.

Placental abnormalities are common in triploidy. Most frequently, the placenta is enlarged and may have cysts within. In some cases, the placenta may be unusually small, having ceased to grow.

Triploid syndrome, also called triploidy, is an extremely rare chromosomal disorder, in which a fetus has three copies of every chromosome instead of the normal two. If this occurs in only some cells, it is called mosaic triploidy, and is less severe.

Malpuech syndrome is congenital, being apparent at birth. It is characterized by a feature known as facial clefting. Observed and noted in the initial description of the syndrome as a cleft lip and palate, facial clefting is identified by clefts in the bones, muscles and tissues of the face, including the lips and palate. The forms of cleft lip and palate typically seen with Malpuech syndrome are midline (down the middle of the lip and palate) or bilateral (affecting both sides of the mouth and palate). Facial clefting generally encompasses a wide range of severity, ranging from minor anomalies such as a (split) uvula, to a cleft lip and palate, to major developmental and structural defects of the facial bones and soft tissues. Clefting of the lip and palate occurs during embryogenesis. Additional facial and ortho-dental anomalies that have been described with the syndrome include: hypertelorism (unusually wide-set eyes, sometimes reported as telecanthus), narrow palpebral fissures (the separation between the upper and lower eyelids) and ptosis (drooping) of the eyelids, frontal bossing (prominent eyebrow ridge) with synophris, highly arched eyebrows, wide nasal root and a flattened nasal tip, malar hypoplasia (underdeveloped upper cheek bone), micrognathia (an undersized lower jaw), and prominent incisors. Auditory anomalies include an enlarged ear ridge, and hearing impairment associated with congenital otitis media (or "glue ear", inflammation of the middle ear) and sensorineural hearing loss.

Another feature identified with Malpuech syndrome is a caudal appendage. A caudal appendage is a congenital outgrowth stemming from the coccyx (tailbone). Present in many non-human animal species as a typical tail, this feature when seen in an infant has been described as a "human tail". This was observed by Guion-Almeida (1995) in three individuals from Brazil. The appendage on X-rays variously appeared as a prominent protrusion of the coccyx. On a physical examination, the appendage resembles a nodule-like stub of an animal tail.

Deficiencies such as mental retardation, learning disability, growth retardation and developmental delay are common. Psychiatric manifestations that have been reported with the syndrome include psychotic behavior, obsessive–compulsive disorder, loss of inhibition, hyperactivity, aggression, fear of physical contact, and compulsive actions like echolalia (repeating the words spoken by another person). Neuromuscular tics have also been noted.

Urogenital abnormalities, or those affecting the urinary and reproductive systems, are common with the syndrome. Malpuech et al. (1983) and Kerstjens-Frederikse et al. (2005) reported variously in affected males a micropenis, hypospadias (a congenital mislocation of the urinary meatus), cryptorchidism ( or undescended testes), bifid (split) and underdeveloped scrotum, and an obstructive urethral valve. An affected boy was also reported by Reardon et al. (2001) with left renal agenesis, an enlarged and downwardly displaced right kidney, cryptorchidism and a shawl scrotum. Other malformations that have been noted with the syndrome are omphalocele and an umbilical hernia.

Congenital abnormalities of the heart have also been observed with Malpuech syndrome. From a healthy Japanese couple, Chinen and Naritomi (1995) described the sixth child who had features consistent with the disorder. This two-month-old male infant was also affected by cardiac anomalies including patent ductus arteriosus (PDA) and ventricular septal defect. The opening in the ductus arteriosus associated with PDA had been surgically repaired in the infant at 38 days of age. A number of minor skeletal aberrations were also reported in the infant, including wormian bones at the lambdoid sutures.

A breech birth occurs when a baby is born bottom first instead of head first. Around 3-5% of pregnant women at term (37–40 weeks pregnant) will have a breech baby.

Most babies in the breech position are born by a caesarean section because it is seen as safer than being born vaginally.

As most breech babies are delivered by caesarean section in developed countries, doctors and midwives may lose the skills required to safely assist women giving birth to a breech baby vaginally. Delivering all breech babies by caesarean section in developing countries may be very difficult to implement or even impossible as there are not always resources available to provide this service.

Of those fetuses that do survive to gestation and subsequent birth, common abnormalities may include:

- Nervous system

- Intellectual disability and motor disorder

- Microcephaly

- Holoprosencephaly (failure of the forebrain to divide properly).

- Structural eye defects, including microphthalmia, Peters' anomaly, cataract, iris or fundus (coloboma), retinal dysplasia or retinal detachment, sensory nystagmus, cortical visual loss, and optic nerve hypoplasia

- Meningomyelocele (a spinal defect)

- Musculoskeletal and cutaneous

- Polydactyly (extra digits)

- Cyclopia

- Proboscis

- Congenital trigger digits

- Low-set ears

- Prominent heel

- Deformed feet known as rocker-bottom feet

- Omphalocele (abdominal defect)

- Abnormal palm pattern

- Overlapping of fingers over thumb

- Cutis aplasia (missing portion of the skin/hair)

- Cleft palate

- Urogenital

- Abnormal genitalia

- Kidney defects

- Other

- Heart defects (ventricular septal defect) (Patent Ductus Arteriosus)

- Dextrocardia

- Single umbilical artery