Hypothyroidism due to any cause can cause misscarriages.
Anti-TPO + with high TSH means like autoimmune hypothyroidism
or hashimotos thyroiditis
Endometrial thickness has nothing to do with thyroid gland.
But it will be very difficult for you to get conceive and maintain pregnancy if your TSh will be hgh than 2.2.
High TSh can cause high prolactin as well and that do lead to less endometrial thickness
is a common thing before or after pregnancy
Hope this helps