Kellie:  This is an interesting situation.  It would be helpful to have
the actual numbers of all her thyroid levels.  There is not usually a
"false normal" from pregnancy.  Pregnancy, oral contraceptives and
hormone replacement can cause the T4 to be falsely high, while the T3RU
is low and the TSH is normal.  This is due to an elevation in a protein
called thyroxine binding globulin, not due to an actual increase in T4
hormone, so it does not mean that the woman is hyperthyroid.  The tipoff
is that the T4 and T3RU are opposite (in true hyper- or hypothyroidism,
both are up or down) The TSH is low with hyper- and high with
hypothyroidism, so it is very useful when questions come up based on the basic panel.
However, in rare cases of pituitary failure, where other pituitary
hormones are also low, the TSH can be low, causing the thyroid to be
underproductive, with all thyroid levels low as a result.  One possible
reason for the TSH to be low when the T4 is normal is T3 toxicosis, so a
T3 by RIA is necessary.  The bottom line is this woman needs a further
evaluation.  If her Ob/gyn doesn't regularly deal with endocrine
problems, perhaps her family physician, internist or even a referral to
an endocrinologist would be appropriate. Alicia.  [log in to unmask]