How Mermaid Syndrome Works

As is sometimes the case with genetic anomalies and mutations, sirenomelia or "mermaid syndrome" conjures certain fanciful images that have nothing to do with the traumatic effects associated with the actual medical anomaly.

Sirenomelia is so named because the birth defect involves the apparent fusing of the legs into a single lower limb, with the out-turned feet often resembling fish fins. The defect also commonly affects the kidneys, large intestines and genitalia. The condition sometimes affects the spine, brain and lungs as well.

According to, this rare condition occurs when a fetus develops only one umbilical artery (which pumps blood from the fetus to the placenta) and one umbilical vein (which returns blood to the fetus), while normal fetuses develop two umbilical arteries and one umbilical vein. The altered arrangement causes less blood and nutrition to reach the lower body, leading to the fused limbs and underdeveloped array of organs.

According to the Madisons Foundation, the condition affects roughly 1 in every 60,000 to 100,000 live births. Of the 300 reported cases, few survived more than several days -- and they required extensive medical care. As far as I can tell, the only living individuals with sirenomelia are Shiloh Pepin of the United States (you can visit her family's Web site here), Milagros Cerrón Arauco of Peru (here's a video on her case) and Tiffany Yorks of the United States.

It's hard not to be awed by these three survival stories. At the same time, does this rare condition receive more media attention due to its sensational aspects? I can't help but think of children born every day with conditions that don't make for as snappy a headline.

For more information on how you can help children with birth deflects and fight preventable defects around the world, visit the the March of Dimes.

Learn more at How Childbirth Works How Pregnancy Works Should you save your baby's umbilical cord blood?'s Birth & Infancy Channel