A 6-week old fetus should have a heart beat of around 100/min. and that should pick up to 140/min by the 8th week of gestation. A lower heart beat is an indication of impending fetal loss. Treatment can be aimed at trying to treat maternal conditions and also fetal conditions, the most common cause is a congenital heart block
. The outcome is not so good but there are instances where the fetal heart rates have picked up with a normal outcome. Wish you good luck.