The value depends on the specific test and what it shows. The blood test for spina bifida was notable for false positives - my doctor in the late 90s told me not to bother with it - but there are other diagnostic tools now that are more accurate. Surgery can be done for infants with spina bifida in the womb, in some cases, so it is worth pursuing if more than one indicator points in that direction.
Thank you for the correction; if I’m wrong, I always want to know! I prefer truth over fondly held wrong opinions.