From the picture it doesn't look like a wart but Seborrheic keratosis.
It is a common non-cancerous skin condition which comes as waxy brown, black or tan elevated skin lesions. There may be itching or needle pricking sensation associated with it sometimes.
The main reason for sudden appearance may link to Hormone dysbalance, Frequent sun exposure, Family history, or Continued exposure to Stress.
Next Steps
Take a proper homeopathic course of treatment where your full case is studied in detail, with keeping in mind your pregnancy so that your individual, specific medicine can be chosen.
Health Tips
Homeopathic medicine do its wonder but you need to have faith and patience. Since the selection of medicine depends on the answers patients give, it is advisable to be as open and forthcoming as you can with your consulting doctor. Spare no tiny details.