what is the risk that i'm taking the 70/30 insuline and i'm pregnant

70/30 insulin is premixed N & R: it's 70% N (also called NPH) and 30% R (also called Regular). So what the doctor advised is to allow you to mix N and R in differing ratios than the 70/30 ratio that's the only one available in the premix.

During pregnancy, it's critical to maintain scrupulous control of your blood glucose levels to protect the developing baby as well as yourself, and many physicians are now using Lantus and Humalog or similar insulins given in a basal-bolus method, rather than using N and R. Talk to your doctor about starting a basal-bolus program, or an insulin pump. If he/she is unfamiliar with these concepts, you should ask for a referral to a full diabetes team for managing your diabetes during pregancy. The team should include an endocrinologist, diabetes nurse educator, and diabetes dietitian. You also will need to have your eyes checked, and of course, you'll want an obstetrician who's used to dealing with diabetes pregnancies.

There's lots of other recommendations for pregnancy: see Planning a Pregnancy.

Hope this helps!