A nuchal cord occurs when the umbilical cord becomes wrapped around the fetal neck 360 degrees. Nuchal cords are common, with prevalence rates of 6% to 37%. Up to half of nuchal cords resolve before delivery.

The first sign of umbilical cord prolapse is usually a sudden decrease in fetal heart rate that is severe and does not immediately resolve. On a fetal heart tracing, this would usually look like moderate to severe variable decelerations. Occasionally, the cord can be seen or felt on vaginal examination, particularly with overt cord prolapse.

There are three types of umbilical prolapse that can occur:

- overt umbilical cord prolapse: descent of the umbilical cord past the presenting fetal part. In this case, the cord is through the cervix and into or beyond the vagina. Overt umbilical cord prolapse requires rupture of membranes. This is the most common type of cord prolapse.

- occult umbilical prolapse: descent of the umbilical cord alongside the presenting fetal part, but has not advanced past the presenting fetal part. Occult umbilical prolapse can occur with both intact or ruptured membranes.

- funic (cord) presentation: presence of the umbilical cord between the presenting fetal part and fetal membranes. In this case, the cord has not passed the opening of the cervix. In funic presentation, the membranes are not yet ruptured.

In 1962, J. Selwyn Crawford MD from the British Research Council defined a nuchal cord as one that is wrapped 360 degrees around the fetal neck. Dr. Crawford commented "It is all the more remarkable, therefore, that little work has been done ... to analyze its effects during labor and delivery". To date, there is no prospective case control double-blind study looking at nuchal cords and observational studies vary in opinion as to the degree of poor outcomes. Also not included in these studies is which umbilical cord form (of the 8 different possible structures) was considered a nuchal cord.

Ultrasound diagnosis of a cord around the neck was first described in 1982. “Coils occur in about 25% of cases and ordinarily do no harm, but occasionally they may be so tight that constriction of the umbilical vessels and consequent hypoxia result.” Williams Obstetrics 16th Edition, has only one single sentence in the entire textbook regarding cords around the neck. By contrast, the First Edition of the Encyclopædia Britannica from 1770 had 20 pages of information about Umbilical Cord Pathology with drawings of Umbilical Cord Entanglement. The Royal College of Obstetricians and Gynaecologists has these images on its brochure. There are currently three recent texts on ultrasonography which demonstrate the ability of ultrasound to identify umbilical cord issues with reliability as of 2009.

A study published in 2004 was done to establish the sensitivity of ultrasound in the diagnosis of a nuchal cord. Each of 289 women, induced the same day, underwent a transabdominal ultrasound scan with an Aloka 1700 ultrasound machine with a 3.5 MHz abdominal probe, using gray-scale and color Doppler imaging immediately prior to induction of labor. Presence of the cord was sought in the transverse and sagittal plane of the neck. A nuchal cord was diagnosed if the cord was visualized lying around at least 3 of the 4 sides of the neck. A cord was actually present at delivery in 52 of the 289 women. Only 18 of the 52 cords or 35% of the nuchal cords were detected on ultrasound done immediately before delivery, and 65% of nuchal cords were not detected. Of the 237 cases where there was no cord at delivery, ultrasound had false positive results, i.e. diagnosed a cord in 44 of the 237 cases (19%) in which there was no cord present at all. In this study, ultrasound was only 35% accurate at finding a single loop, and only 60% accurate at detecting a nuchal cord wrapped multiple times around the neck.

In no study was it possible by ultrasound to distinguish between a loose or a tight cord, although at least 3 attempted to do so. Peregrine concludes that ultrasound diagnosis of nuchal cords will only be useful if doctors are able to do so reliably and predict which of those fetuses are likely to have a problem., However, perinatologists routinely look for umbilical cord issues in monoamniotic twins. Studies have shown an improvement in outcomes where cord entanglement was prenatally identified in these cases. Ultrasound measurement of the velocity of flow in the cord may be useful in the management of twins and chronically growth-retarded fetuses. Of course this depends on the training of the sonographer. To date there are no ultrasound courses which teach the identification of nuchal cord to physicians or technicians. A recent review by Wilson of the American Academy of Ultrasonography Technicians recommends the documentation of umbilical cord issues.

Clapp, et al, attempted to find out at what rate nuchal cords come and go during pregnancy. He recruited 84 healthy, non-smoking, non-substance abusing women carrying a single fetus, with certain dates before the 20th week of gestation. They all agreed to 4 extensive ultrasounds at 24-26, 30-32, 36–38 weeks gestation and during labor and delivery. They evaluated fetal biometry, fetal tone, fetal motion including breathing movements, amniotic fluid volume, fetal flow redistribution, velocity flow profiles from the umbilical artery at the body wall and placental insertion and at the origin of fetal middle cerebral artery. Finally, color flow Doppler imaging was used to determine whether a nuchal cord was present. Clapp reports that in 60%, or 50 of the 84 fetuses studied, a nuchal cord was seen on ultrasound at one of the 4 evaluations. He found that the presence of a nuchal cord linearly increases as the pregnancy continues. Larson, et al, found this to be true. She found, of the 13,895 singleton deliveries, a nuchal cord linearly increased every week of gestation, appearing in 6% at 20 weeks to 29.0% at 42 weeks gestation.

On cardiotocography (CTG), umbilical cord compression can present with variable decelerations in fetal heart rate.

Umbilical cord compression may be relieved by the mother switching to another position. In persistent severe signs of fetal distress, Cesarean section may be needed.

Velamentous cord insertion is an abnormal condition during pregnancy. Normally, the umbilical cord inserts into the middle of the placenta as it develops. In velamentous cord insertion, the umbilical cord inserts into the fetal membranes (choriamniotic membranes), then travels within the membranes to the placenta (between the amnion and the chorion). The exposed vessels are not protected by Wharton's jelly and hence are vulnerable to rupture. Rupture is especially likely if the vessels are near the cervix, in which case they may rupture in early labor, likely resulting in a stillbirth. This is a serious condition called vasa previa. Not every pregnancy with a velamentous cord insertion results in vasa previa, only those in which the blood vessels are near the cervix.

When a velamentous cord insertion is discovered, the obstetrician will monitor the pregnancy closely for the presence of vasa previa. If the blood vessels are near the cervix, the baby will be delivered via cesarean section as early as 35 weeks to prevent the mother from going into labor, which is associated with a high infant mortality. Early detection can reduce the need for emergency cesarean sections.

Symptoms vary depending on whether the spinal cord, brain stem, nerves or their blood supply is affected by the pressure.

Symptoms become apparent when the neck is bent. They include:

- Posterior head pain

- Neck weakness

- Periods of confusion

- Dysarthria (difficulty swallowing or talking due to loss of muscle control)

- Dizziness

- Loss of sensation

- Cranial nerve disturbance

- Loss of the ability to know how joints are positioned

- Lhermitte's sign ('electric shock sensation' down spine and/or to the extremities when the neck is flexed forward)

- Weakness of the arms and legs

- Orthostatic hypotension

- Patients will go into a pool and notice that below their belly button the water is not as cold as it is above.

Complications from this can include hydrocephalus, pseudotumor cerebri or syringomyelia because it blocks the flow of fluid around the brain and spinal cord.

The signs and symptoms of diastematomyelia may appear at any time of life, although the diagnosis is usually made in childhood. Cutaneous lesions (or stigmata), such as a hairy patch, dimple, Hemangioma, subcutaneous mass, Lipoma or Teratoma override the affected area of the spine is found in more than half of cases. Neurological symptoms are nonspecific, indistinguishable from other causes of cord tethering. The symptoms are caused by tissue attachments that limit the movement of the spinal cord within the spinal column. These attachments cause an abnormal stretching of the spinal cord.

The course of the disorder is progressive. In children, symptoms may include the "stigmata" mentioned above and/or foot and spinal deformities; weakness in the legs; low back pain; scoliosis; and incontinence. In adulthood, the signs and symptoms often include progressive sensory and motor problems and loss of bowel and bladder control. This delayed presentation of symptoms is related to the degree of strain placed on the spinal cord over time.

Tethered spinal cord syndrome appears to be the result of improper growth of the neural tube during fetal development, and is closely linked to spina bifida.

Tethering may also develop after spinal cord injury and scar tissue can block the flow of fluids around the spinal cord. Fluid pressure may cause cysts to form in the spinal cord, a condition called syringomyelia. This can lead to additional loss of movement, feeling or the onset of pain or autonomic symptoms.

Cervical diastematomyelia can become symptomatic as a result of acute trauma, and can cause major neurological deficits, like hemiparesis, to result from otherwise mild trauma.

The following definitions may help to understand some of the related entities:

- Diastematomyelia (di·a·stem·a·to·my·elia) is a congenital anomaly, often associated with spina bifida, in which the spinal cord is split into halves by a bony spicule or fibrous band, each half being surrounded by a dural sac.

- Myeloschisis (my·elos·chi·sis) is a developmental anomaly characterized by a cleft spinal cord, owing to failure of the neural plate to form a complete neural tube or to rupture of the neural tube after closure.

- Diplomyelia (diplo.my.elia) is a true duplication of spinal cord in which these are two dural sacs with two pairs of anterior and posterior nerve roots.

In children, symptoms may include:

- Lesions, hairy patches, dimples, or fatty tumours on the lower back

- Foot and spinal deformities

- Weakness in the legs (loss of muscle strength and tone)

- Change in or abnormal gait including awkwardness while running or wearing the tips or side of one shoe

- Low back pain

- Scoliosis (abnormal curvature of the spine to the left or right)

- Urinary irregularities (incontinence or retention)

Tethered spinal cord syndrome may go undiagnosed until adulthood, when sensory, motor, bowel, and bladder control issues emerge. This delayed presentation of symptoms relates to the degree of strain on the spinal cord over time.

Tethering may also develop after spinal cord injury. Scar tissue can block the flow of fluids around the spinal cord. Fluid pressure may cause cysts to form in the spinal cord, a condition called syringomyelia. This can lead to additional loss of movement or feeling, or the onset of pain or autonomic nervous system symptoms.

In adults, onset of symptoms typically include:

- Severe pain (in the lower back and radiating into the legs, groin, and perineum)

- Bilateral muscle weakness and numbness

- Loss of feeling and movement in lower extremities

- Urinary irregularities (incontinence or retention)

- Bowel control issues

Neurological symptoms can include a mixed picture of upper and lower motor neuron findings, such as amyotrophy, hyperreflexia, and pathologic plantar response, occurring in the same limb. Profound sensory changes, such as loss of pain, temperature, and proprioceptive sensations, are common. Last, progressive symptoms of a neuropathic bladder are noted on over 70% of adult patients, versus only 20% to 30% of children. These symptoms include urinary frequency and urgency, feeling of incomplete voiding, poor voluntary control, and urge and stress incontinence. Chronic recurrent infections are common and occasionally lead to nephrolithiasis (kidney stones), renal failure, or renal transplantation. Female patients also give a history of ineffective labor and postpartum rectal prolapse, presumably due to an atonic pelvic floor.

Twin reversed arterial perfusion sequence—also called TRAP sequence, TRAPS, or acardiac twinning—is a rare complication of monochorionic twin pregnancies. It is a severe variant of twin-to-twin transfusion syndrome (TTTS). The twins' blood systems are connected instead of independent. One twin, called the "acardiac twin" or "TRAP fetus", is severely malformed. The heart is missing or deformed, hence the name acardiac, as are the upper structures of the body . The legs may be partially present or missing, and internal structures of the torso are often poorly formed. The other twin is usually normal in appearance. The normal twin, called the "pump twin", drives blood through both fetuses. It is called "reversed arterial perfusion" because in the acardiac twin the blood flows in a reversed direction.

TRAP sequence occurs in 1% of monochorionic twin pregnancies and in 1 in 35,000 pregnancies overall.

Syringomyelia is a generic term referring to a disorder in which a cyst or cavity forms within the spinal cord. This cyst, called a syrinx, can expand and elongate over time, destroying the spinal cord. The damage may result in loss of pain, paralysis, weakness, and stiffness in the back, shoulders, and extremities. Syringomyelia may also cause a loss of the ability to feel extremes of hot or cold, especially in the hands. It may also lead to a cape-like bilateral loss of pain and temperature sensation along the upper chest and arms. Each patient experiences a different combination of symptoms. These symptoms typically vary depending on the extent and, often more critically, to the location of the syrinx within the spinal cord.

Syringomyelia has a prevalence estimated at 8.4 cases per 100,000 people, with symptoms usually beginning in young adulthood. Signs of the disorder tend to develop slowly, although sudden onset may occur with coughing, straining, or myelopathy.

Syringomyelia causes a wide variety of neuropathic symptoms due to damage of the spinal cord and the nerves inside. Patients may experience severe chronic pain, abnormal sensations and loss of sensation particularly in the hands. Some patients experience paralysis or paresis temporarily or permanently. A syrinx may also cause disruptions in the parasympathetic and sympathetic nervous systems, leading to abnormal body temperature or sweating, bowel control issues, or other problems. If the syrinx is higher up in the spinal cord or affecting the brainstem as in syringobulbia, vocal cord paralysis, ipsilateral tongue wasting, trigeminal nerve sensory loss, and other signs may occur. Rarely, bladder stones can occur in the onset of weakness in the lower extremities.

Classically, syringomyelia spares the dorsal column/medial lemniscus of the spinal cord, leaving pressure, vibration, touch and proprioception intact in the upper extremities. Neuropathic arthropathy, also known as a Charcot joint, can occur, particularly in the shoulders, in patients with syringomyelia. The loss of sensory fibers to the joint is theorized to lead to damage of the joint over time.

Symptoms usually occur very quickly and are often experienced within one hour of the initial damage. MRI can detect the magnitude and location of the damage 10–15 hours after the initiation of symptoms. Diffusion-weighted imaging may be used as it is able to identify the damage within a few minutes of symptomatic onset.

Clinical features include paraparesis or quadriparesis (depending on the level of the injury) and impaired pain and temperature sensation. Complete motor paralysis below the level of the lesion due to interruption of the corticospinal tract, and loss of pain and temperature sensation at and below the level of the lesion. Proprioception and vibratory sensation is preserved, as it is in the dorsal side of the spinal cord.

Rachischisis (Greek: "rhachis - ῥάχις" - spine, and "schisis - σχίσις" - split) is a developmental birth defect involving the neural tube. This anomaly occurs in utero, when the posterior neuropore of the neural tube fails to close by the 27th intrauterine day. As a consequence the vertebrae overlying the open portion of the spinal cord do not fully form and remain unfused and open, leaving the spinal cord exposed. Patients with rachischisis have motor and sensory deficits, chronic infections, and disturbances in bladder function. This defect often occurs with anencephaly.

Craniorachischisis is a variant of rachischisis that occurs when the entire spinal cord and brain are exposed - simultaneous complete rachischisis and anencephaly. It is incompatible with life; affected pregnancies often end in miscarriage or stillbirth. Infants born alive with craniorachischisis die soon after birth.

Basilar invagination is invagination (infolding) of the base of the skull that occurs when the top of the C2 vertebra migrates upward. It can cause narrowing of the foramen magnum (the opening in the skull where the spinal cord passes through to the brain). It also may press on the lower brainstem.

This is similar to Chiari malformation. That, however, is usually present at birth.

Posterior spinal artery syndrome is much rarer than its anterior counterpart as the white matter structures that are present are much less vulnerable to ischemia since they have a better blood supply. When posterior spinal artery syndrome does occur, dorsal columns are damaged and ischemia may spread into the posterior horns. Clinically the syndrome presents as a loss of tendon reflexes and loss of joint position sense

Tethered spinal cord can be caused by various conditions but the main cause is when tissue attachments limit the movement of the spinal cord in the spinal column which causes abnormal stretching of the cord. The tethered spinal cord syndrome is correlated with having the causes:

- Spina bifida

- Occulta

- Mylomeningocele

- Meningocele

- History of spinal trauma

- History of spinal surgery

- Tumor(s) in the spinal column

- Thickened and/or tight filum terminale

- Lipoma(s) in the spinal column

- Dermal Sinus Tract (congenital deformity)

- Diastematomyelia (split spinal cord)

Tethered spinal cord is a disorder and not a mechanism so it does not spread to other people and there are no measures that can be done to prevent it beforehand. The only preventative measure that is successful is to surgically untether the spinal cord though there might already be irreversible damage.

Treatment is determined based on the primary cause of anterior cord syndrome. When the diagnosis of anterior cord syndrome is determined, the prognosis is unfortunate. The mortality rate is approximately 20%, with 50% of individuals living with anterior cord syndrome having very little or no changes in symptoms.

Diastematomyelia (occasionally diastomyelia) is a congenital disorder in which a part of the spinal cord is split, usually at the level of the upper lumbar vertebra.

Diastematomyelia is a rare congenital anomaly that results in the "splitting" of the spinal cord in a longitudinal (sagittal) direction. Females are affected much more commonly than males. This condition occurs in the presence of an osseous (bone), cartilaginous or fibrous septum in the central portion of the spinal canal which then produces a complete or incomplete sagittal division of the spinal cord into two hemicords. When the split does not reunite distally to the spur, the condition is referred to as a diplomyelia, or true duplication of the spinal cord.

Transient ischemic attacks (TIAs) rarely affect the spinal cord and usually affect the brain; however, cases have been documented in these areas. Spinal ateriovenous malformations are the main cause and are represented later in this article. However, TIAs can result from emboli in calcific aortic disease and aortic coarctation.

The onset of myelomalacia may be so subtle that it is overlooked. Depending on the extent of the spinal cord injury, the symptoms may vary. In some cases, the symptom may be as common as hypertension. Though every case is different, several cases reported loss of motor functions in the extremities, areflexia or sudden jerks of the limbs, loss of pain perception, or even paralysis; all of which are possible indicators of a damaged and softened spinal cord. In the most severe cases, paralysis of the respiratory system manifests in death.

Foix–Alajouanine syndrome is a disorder caused by an arteriovenous malformation of the spinal cord. The patients present with symptoms indicating spinal cord involvement (paralysis of arms and legs, numbness and loss of sensation and sphincter dysfunction), and pathological examination reveals disseminated nerve cell death in the spinal cord and abnormally dilated and tortuous vessels situated on the surface of the spinal cord. Surgical treatment can be tried in some cases. If surgical intervention is contraindicated, corticosteroids may be used.

The condition is named after Charles Foix and Théophile Alajouanine.

The acardiac twin is a parasitic twin that fails to properly develop a heart, and therefore generally does not develop the upper structures of the body. The parasitic twin, little more than a torso with or without legs, receives its blood supply from the host twin by means of an umbilical cord-like structure (which often only has 2 blood vessels, instead of 3), much like a fetus in fetu, except the acardiac twin is outside the host twin's body. Although the reason is not fully understood, it is apparent that deoxygenated blood from the pump twin is perfused to the acardiac twin. The acardiac twin grows along with the pump twin, but due to inadequate oxygenation it is unable to develop the structures necessary for life, and presents with dramatic deformities.

Although no two acardiac twins are alike, twins with this disorder are grouped into 4 classes: Acephalus, anceps, acormus, and amorphus.

- Acephalus – The most common type, lacking a head, though it may have arms. Thoracic organs are generally absent, and disorganized & unidentifiable tissues take their place.

- Anceps – The acardius has most body parts, including a head with face and incomplete brain. Organs, though present, are crudely formed.

- Acormus – This type has no apparent body and the umbilical cord is seemingly attached to the neck, but x-rays or dissection reveal thoracic structures in the apparent head. One had a leg apparently attached to the head. This may be due to embryopathy degenerating a once normal embryo.

- Amorphus – This extreme form not only lacks a head and limbs, but also any internal organs, and consists of tissues with blood vessels branching from the umbilical cord. Some may only be stem cell tumors.

The acardiac twin may also be described as a "hemiacardius", which has an incompletely formed heart, or a "holoacardius", in which the heart is not present at all.

SCIWORA may present as a complete spinal cord injury (total loss of sensation and function below the lesion) or incomplete spinal cord injury (some sensation and/or function is preserved). It is present in a significant number of children with SCI. Notably, the clinical symptoms can present with a delay of hours to days after the trauma. This phenomenon was primarily seen in children but was reported in adults as well. The duration of symptoms varies widely. A full recovery can be achieved without treatment within minutes to hours and permanent injuries might prevail. Overall, there seems to be a relation between extent of damage to the spinal cord and the clinical prognosis. The prognostic value of intra- and extra-medullary MRI findings is subject of ongoing research in the field of SCIWORA.