by: Crystal Jang

What is Sirenomelia?

Sirenomelia is a lethal condition characterised by rotation and fusion of the legs, resulting in what often looks like a fish tail. It occurs when the umbilical cord fails to form two arteries, thus preventing a sufficient blood supply from reaching the fetus. As a result, the single artery steals the blood and nutrition from the lower body and diverts it back up to the placenta. Due to malnutrition, the fetus fails to develop two separate limbs.


Treatment is applicable for newborns who survive even 24 hours after delivery. Affected newborns having functioning kidneys are recommended for surgical procedures and management. Surgical operations to rebuild the gastrointestinal and urinary outlet tracts are essential for such patients. The extent of procedures and therapies for Mermaid syndrome patients depends on the severity of the birth defect.

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Since the actual reason for Mermaid syndrome is still unknown, doctors cannot recommend procedures and safety guidelines to prevent its occurrence. Hence, the prevention of this severe form of caudal regression is almost impossible.


Sirenomelia sequence is characterized by the developing symptoms and signs that signify its occurrence. The primary indicators are fused feet and legs along with a number of warning signs including:

  • Miniature, fused, small and poorly structured pelvic bones
  • Malfunctioning kidneys
  • Imperforated anus
  • Blind ending colon
  • Inborn anomaly in the upper portions of the body including lungs, heart, arms, brain and spine
  • Poorly structured and small external and internal genitalia
  • Immature and underdeveloped lungs arising due to oligohydramnios, often leading to death.


Physicians recommend that physical examination of newborn baby is mandatory to determine the diagnosis. A few tests which help to detect the existence of Mermaid syndrome among the infants include:


This procedure helps to conduct the prenatal diagnosis which is obvious at the second trimester of pregnancy.


This procedure helps to perform an antenatal diagnosis of Sirenomelia sequence and helps doctors to determine the right treatment option for it.


The exact cause of sirenomelia is unknown. Researchers believe that both environmental and genetic factors may play a role in the development of the disorder. Most cases appear to occur randomly for no apparent reason (sporadically), which suggests environmental factors or a new mutation. Most likely, sirenomelia is multifactorial, which means that several different factors may play a causative role. In addition, different genetic factors may contribute to the disorder in different people (genetic heterogeneity).

Mermaid syndrome occurs due to abnormal development of the umbilical cord blood vessels. Normally umbilical cord contains two umbilical arteries and one umbilical vein. In sirenomelia there is one of each. Even if there are two arteries one of them is blocked. This is what causes improper development of legs and prevent their separation.

The condition may be caused by certain illnesses which affect either the mother or the fetus, improper and poor prenatal care by the expectant mother and there is also a theory that genetic abnormalities may be a culprit of this syndrome.

Is this sex-linked, a mutation, or is it due to heredity?

Nobody knows the answer... YET!



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More about Sirenomelia

  • Sirenomelia, also known as ‘Mermaid Syndrome’, is extremely rare. It affects 1 in 100,000 babies and is 100 times more likely to occur in identical twins. Usually, those born with this condition die within days.
  • commonly found in males
  • Sirenomelia got its name from Greek Mythology. A siren was an animal with a head of a woman, tail of a bird. Until sirens were seen more of an aquatic animal.
  • SIrenomelia is also known as Mermaid Syndrome because of the physical looks.

History of Sirenomelia

  • There are very small snippets about this disease in the past but here are snippets here and there which claim that fetuses born with sirenomelia were sometimes preserved in jars and put on display in ‘freak shows’ during the 19th century—but these sources are frustratingly vague. There is brief mention of the condition in a four-volume atlas published in 1891 titled Human Monstrosities, but nothing that hints at how medical practitioners understood sirenomelia in earlier periods.
  • There are however, are some history found in the early 20th-century example at the National Museum of Health and Medicine in Washington D.C. There are also three fetuses in the Anatomical Museum of the Second University of Naples, which have undergone 3D bone reconstructions (two pictured below).