Can lou gehrig's disease be detected before birth?

No. There is no available technique, either via ultrasound or amniocentesis which can do this.
Lou Gehrig. Lou gehrig's disease is a disorder of adults and not child. I am not aware of any diagnostic tests that determine a fetus has lou gehrig's disease.
No. Approximately 14 cases of ALS are diagnosed each day nationwide. Most of those who develop the disease are between 40 and 70 years of age. The average expected survival time for those suffering from ALS is three to five years. At any given time, approximately 30, 000 people in the United States are living with the disease. The cause of ALS remains unclear, and no cure exists.