Our baby was born without a sacral bone. I took prenatal vitamins, I did yoga and Tai chi, I was very careful with my diet. What could I have done wrong?

You may not be at fault in any way. Sometimes nature takes its own course and it has nothing to do with our actions or inactions.

Sacral agenesis (the absence of a sacral bone at the base of the spine) is uncommon, but not unheard of. About one in every 25,000 children born have some kind of sacral anomaly or defect. Sometimes, the bone is completely missing as with your child. In other cases, only half of the sacrum is present or there may be a part missing on both sides.

Depending on the type of sacral agenesis that is present, there may be bowel or bladder problems as well. Again, no one is exactly sure why this deformity occurs. There’s a link between mothers with diabetes and children born with sacral agenesis. But what the connection is to diabetic-related insulin deficiency (if there is one), remains a mystery.

Scientists have also identified specific genetic mutations that may be inherited. In families with this trait, there may be more than one child born with sacral agenesis. There have also been reports of certain drugs being linked with sacral agenesis. For example, the antiobiotics minoxidil and septra and other drugs such as appetite suppressants have been associated with this birth defect.

Animal research has linked certain solvents and chemicals (e.g., sulfamides, lithium, retinoic acid) with sacral defects. But there doesn’t seem to be one particular cause that is consistently linked with this problem. It may be multifactorial, meaning that when several factors are present at the same time or combined together, then something gets disrupted in the formation of this part of the body.