Folic acid supplements and risk of facial clefts: national population based case-control study

There were three sources of data on possible "other defects" in our
clefts cases: the original Birth Registry record filled out at birth, the
record of the surgery clinic performing the corrective surgery, and the
mother's questionnaire completed after birth. If any of these three
sources reported that a case had any birth defect in addition to the
cleft, we excluded that case from the analyses restricted to "isolated
clefts."

I hope this answers your question. If not, feel free to contact me
directly at wilcox@niehs.nih.gov.

Competing interests:
None declared