While the exact cause is unknown, it has been speculated that the condition has a combination of environmental and genetic causes, and that various types of the condition may have differing causes.Sacral agenesis syndrome (a type of caudal regression syndrome involving agenesis of the lumbar spine, sacrum, and coccyx, and hypoplasia of the lower extremities) is a well-established congenital anomaly associated with maternal diabetes mellitus. Other causes are presumably involved, as demonstrated by the rare overall incidence of caudal regression syndrome (1:60,000) compared to diabetes; however, the condition does have a greatly increased incidence among infants born to mothers with diabetes, estimated at 1 in 350 newborns of mothers with diabetes.The dominant inherited sacral agenesis (also referred to as Currarino syndrome) is very often correlated with a mutation in the Hb9 (also called HlxB9) gene (shown by Sally Ann Lynch, 1995, Nature Genetics).It was previously thought to be related to sirenomelia ("Mermaid syndrome") but has now been determined not to be related to this condition. Prognosis
There are four levels (or types) of malformation. The least severe indicates partial deformation (unilateral) of the sacrum. The second level indicates a bilateral (uniform) deformation. The most severe types involve a total absence of the sacrum.Depending on the type of sacral agenesis, bowel or urinary bladder deficiencies may be present. A permanent colostomy may be necessary in the case of imperforate anus. Incontinence may also require some type of continence control system (e.g., self-catheterization) be utilized.
Twin-to-twin transfusion syndrome (TTTS), also known as feto-fetal transfusion syndrome (FFTS), twin oligohydramnios-polyhydramnios sequence (TOPS) and stuck twin syndrome, is a complication of monochorionic multiple pregnancies (the most common form of identical twin pregnancy) in which there is disproportionate blood supply between the fetuses. This leads to unequal levels of amniotic fluid between each fetus and usually leads to death of the undersupplied twin and, without treatment, usually death or a range of birth defects or disabilities for a surviving twin, such as underdeveloped, damaged or missing limbs, digits or organs (including the brain), especially cerebral palsy.The condition occurs when the vein–artery connections within the fetuses shared placenta allow the blood flow between each fetus to become progressively imbalanced. It usually develops between week 16 and 25 of pregnancy, during peak placental growth. The cause of the developmental effects on a surviving fetus may include necrotic embolisms from a dead fetus, low blood volume due to pooling in the dead fetus or velamentous cord insertion (insertion of the umbilical cord into the chorioamniotic membranes).The primary treatment of TTTS is fetoscopy and laser ablation of the interconnecting blood vessels to cut off the exchange of blood between the fetuses. This treatment is associated with an 85% survival rate of at least one fetus. Other treatments include periodic removal of amniotic fluid (serial amniocentesis), which is associated with a 66% survival rate of at least one fetus. Without treatment, there is an almost 100% mortality rate of one or all fetuses.