If you are a borderline thyroid
patient (? hypothyroid) then please make sure you take treatment for that as it is a MUST procedure for a pregnant lady irrespective of the nature of hypothyroidism- permanent one or temporary one, borderline or frank one.
The high doses of gestin
are given for sustainance of pregnancy
. You have not mentioned if you have had any history of miscarriages. But in difficult and precious pregnancies the OB people prefer to give Gestin these days. Generally no major side effects in a pregnant woman as it is pro-pregnancy hormone.