THYROID DISEASE

A   23-year-old primigravida    is  at  30  weeks’  gestation.  She has lost    4   pounds

during  the past    two months. She states  her heart   “feels  like    it  is  racing,”    and

her resting pulse   is  135 beats/min.  There   is  a   noticeable  tremor  when    she

holds   her arms    out straight.   Her eyes    appear  prominent   and protruding. She

is  complaining of  frequent    uterine contractions.

In normal thyroid physiology, increased thyroid blood flow leads to
thyromegaly. In pregnancy, increased glomerular filtration rate (GFR) enhances
iodine excretion, lowering plasma iodine concentrations. Estrogen causes an
increase in liver-produced thyroid binding globulin (TBG), thus increasing total
T3 and T4. However, free T3 and T4 remain unchanged. Fetal thyroid
function begins as early as 12 weeks with minimal transfer of T3 or T4 across
the placenta.