What are the other Names for this Condition? (Also known as/Synonyms)

• Mermaid Syndrome
• Midline Disorder
• Sirenomelia Sequence

What is Sirenomelia? (Definition/Background Information)

• Sirenomelia is an extremely rare medical condition (birth defect) characterized by complete and partial fusion of both legs. It is also known as the Mermaid Syndrome
• Sirenomelia is usually diagnosed before birth, around the second trimester, by fetal ultrasound or sonogram. If diagnosed early in the pregnancy and depending on the severity of the syndrome, the healthcare provider may advice the expectant parents on the potential risks of continuing the pregnancy
• Currently, the exact cause of Sirenomelia is not known, although both environmental and genetic factors could be involved. It is also believed by the medical and scientific community that the missing umbilical artery and vein during gestation, may contribute to the disorder
• Most of the fetuses either die in the womb or survive a few hours or days after birth. Sirenomelia is associated with a number of other congenital anomalies as well, and the associated prognosis is not considered to be good
• If a baby survives the time period following birth (neonatal period), a surgical separation of the lower extremity may be recommended, depending upon the health status of the baby 

Who gets Sirenomelia? (Age and Sex Distribution)

• Sirenomelia is a rare disorder, reportedly affecting one in 60,000-100,000 pregnancies
• The disorder affects developing fetusus of both genders. Based on current statistics, male fetuses are reported to be more susceptible to Sirenomelia than female fetuses (a male-female ratio of 2.7:1 has been noted)
• When compared to fraternal twins or single pregnancies, the chances of developing this condition is greater in identical twin pregnancy (in one of the twin babies)

What are the Risk Factors for Sirenomelia? (Predisposing Factors)

The following are some suspected risk factors for a fetus developing Sirenomelia:

• Being a developing male fetus
• Being one twin of identical twins during gestation: The fetus of an identical twin has a greater risk for developing Sirenomelia than a fetus of a fraternal twin or a single pregnancy
• Early developmental impairment as a result of a fetus having only one umbilical artery and vein, in place of two each. During gestation, the developing fetus with one umbilical artery instead of two, is considered a risk factor for Sirenomelia

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Sirenomelia? (Etiology)

The exact cause of Sirenomelia is not known. However, the scientific and medical communities believe that:

• Certain genetic factors that predispose an individual to the disorder may play a role. These genetic factors may get triggered under certain specific environmental conditions and lead to Sirenomelia
• A developmental abnormality, in which there is only one umbilical artery in place of two, restricts the supply of blood to the lower portions of the fetus is a possible factor that can contribute to Sirenomelia

What are the Signs and Symptoms of Sirenomelia?

Some signs and symptoms associated with Sirenomelia include:

• Fused legs or absence of foot structures (most typical sign)
• Abnormal kidneys
• Vertebral/spine abnormalities
• Absence of genitalia
• Incomplete or underdeveloped reproductive system 

How is Sirenomelia Diagnosed?

• Sirenomelia is usually diagnosed before birth, around the second trimester through fetal ultrasound or sonogram
• A physical examination of the baby immediately after birth is sufficient to diagnose Sirenomelia

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Sirenomelia?

The severity of Sirenomelia varies among babies. Many babies die during birth; those who survive may face severe complications including: 

• Renal abnormalities, such as kidney failure, or absence of either one or both kidneys
• Heart conditions
• Pulmonary defects include immature, small, or abnormal lungs structures
• Absence of bladder, large and small intestines, and other organs
• Severe abnormalities in the upper extremities (arms)
• Severe abnormalities in the brain or spine
• Inability to walk or move normally without help/assistance
• Urethral agenesis, which is the congenital absence of urethra

How is Sirenomelia Treated?

Treatment of Sirenomelia during pregnancy:

• If diagnosed early in pregnancy, then depending on the severity of the syndrome, the healthcare provider may advice on the potential risks of carrying on with the pregnancy

Treatment of Sirenomelia after birth:

• Surgical separation of the lower extremity may be attempted, if the child is healthy enough for a surgical procedure
• In some cases, the child’s lower extremity may have to be amputated
• If organs that process waste are absent in a child, an external waste pouch may have to be created
• Kidney transplant may be considered, if original kidneys fail or are absent
• Reconstructive surgeries may be necessary to enable proper body functioning

How can Sirenomelia be Prevented?

• There are no reported methods of preventing Sirenomelia
• Regular visits to a healthcare provider during pregnancy might facilitate early detection of any abnormality in the fetus. In such cases, necessary steps can be taken to address the medical issues

What is the Prognosis of Sirenomelia? (Outcomes/Resolutions)

• If Sirenomelia is diagnosed early in the pregnancy, the expectant parents may be advised on the future course of action that can be taken
• Those who make it through birth, typically survive for a couple of hours or days
• Overall, the prognosis of Sirenomelia is not favorable

Additional and Relevant Useful Information for Sirenomelia:

The following DoveMed website link is a useful resource for additional information:

http://www.dovemed.com/diseases-conditions/rare-disorders/