Thanks for writing to health care magic.
I can understand your concern.
You should have described the spots and their location. Certain pigmented lines like linea nigra which is a dark line from the umbilicus
to pubis appear during the second trimester. Any way since you are going for a ultrasound
tomorrow discuss with your doctor the same. Most of these are normal during pregnancy
Continue to ask further queries as required.
Hope this helps.
Dr Y V Siva Sankara Murty
Associate Professor of Pediatrics