Hi i just reasonly notice a light brownish line vertical going down my thumb and my index finger. i never notice it before. i'm also in my second trim?

Hyperpigmentation : It is really common in pregnancy to have increased pigmentation/darkening of skin although this is typically seen on the face and belly. You may find this link helpful https://www.dermnetnz.org/topics/skin-problems-in-pregnancy/

Melanocytic hyperpla: Melanocytic hyperplasia caused by a proliferation of melanocytes within the nail matrix or nail bed epithelium is a diagnostic challenge for the clinician and the pathologist. Differentiating a benign pigmented lesion of the nail (lentigo or nevus) from early nail melanoma may be extremely difficult. Please see a dermatologist as melaonma is real and serious