I live in nz (iodine-deficient soil), 6 weeks pregnant, hypothyroid, take 100mcg levo a day and have been advised not to take iodine. is this right?

Iodine deficiency: You need to know the cause of your hypothyroidism. If it is iodine deficiency, then you need iodine supplement. If it is autoimmune thyroiditis (Hashimoto's in most cases), then it has nothing to do with iodine deficiency and iodine supplement is not going to be helpful. Sounds like it's the latter in your case if you are taking levothyroid.

Good question: It is usual practice to monitor thyroid levels and increase Levothyroxine dose - typically we expect an increase of 50% - this will take care of maternal needs however NZ does have low iodine levels http://www.health.govt.nz/our-work/preventative-health-wellness/nutrition/iodine and iodine supplementation is typically recommended in pregnancy and breastfeeding for foetal and infant development.