085 - Tiroide e Gravidanza: Le risposte del laboratorio
Rivista: RIMeL - IJLaM, Vol. 4, N. 3-S1, 2008 (MAF Servizi srl ed.)
E. Toffalori, P. Caciagli
During pregnancy hormonal and metabolical variations
occur and may determine a physiological modification of
the thyroid functionality both in healthy women and those
with thyroid pathology. Few weeks after conception, se-
rum TBG increases two- to three-fold. This leads to an
increase in the total amount of thyroid hormones of 1.5
times greater than pre-pregnancy values, since these hor
mones sharply increase in the first weeks and plateau in the
second trimester. There is now consensus that serum FT4
and FT3 levels decrease below the normal mean in the
second and third trimesters. This decrease in free hormone
is further amplified when the iodine nutrition status of
the mother is restricted or deficient. Changes in FT4 concentrations
during pregnancy are controversial and may
be attributable to the diverse techniques used for measurement.
In the first trimester of pregnancy the greatest concentra-
tion of hCG occurs, which is associated to a decrease in
serum TSH levels that may also reach 20%. The hCG ßsubunits
has thyroid-stimulating activity since it becomes
attached to the TSH receptor of the thyroid. This leads to
an increase in iodide uptake, cAMP production and thyroid
hormone secretion with a TSH decrease. The renal clearance
of iodide increases and during pregnancy iodine intake
should double. These changes can complicate the interpretation
of maternal thyroid function tests, also because
of the frequency of the sub-clinic thyroid disorders
both in women and during pregnancy. In recent years several
studies have demonstrated that the use of reference
intervals of normal people for pregnant women leads to
an underestimation of deficiencies in the maternal thyroid
functionality with a high level of risk for both the mother
and the neurological development of the fetus and child.