Pregnant women shouldn't drink. It's become gospel, because of the danger of fetal alcohol spectrum disorder. Alcohol can disturb the normal development of a fetus, leading to a lifetime of learning disabilities and social problems. But the percentage of children born with the disorder has remained constant, despite the warnings. And not all fetuses of drinking mothers suffer. Now research with rats has shown why some fetuses are naturally protected. Which could lead to ways to protect the vulnerable ones. The work is in the FASEB Journal. The key is a gene called Di03, which governs the levels of thyroid hormone in the brain. If mom passes on a normal Di03, no problem. And a male fetus that inherits a problem Di03 variation from mom but a normal Di03 from dad should be okay. But alcohol can stop dad's normal Di03 gene from working. Now mom's bad Di03 allows the brain to be flooded with thyroid hormone, damaging the hippocampus. The hope is that gene screening could ID women whose fetuses would be at-risk, and that dietary supplements or drugs could block alcohol's effect. And keep a child from suffering from a parent's addiction.