During pregnancy, the target TSH level, as recommended by the American Thyroid Association, is 0.3-3.0 mIU/L, T3 ranges from 80 to 200 nanograms per deciliter (ng/dL), and T4 ranges between 4.5 and 11.7 mcg/dL. Still, the laboratory or doctor might use a slightly different range. When both T3 and T4 are very low, it is considered to be hypothyroidism. Make sure that the TSH levels are monitored and reviewed every six weeks throughout the pregnancy.