The influence of parity on multinodular goiter prevalence in areas with moderate iodine deficiency.

Despite the observation that parity may increase the risk of thyroid carcinoma, very few studies have investigated the possible repercussion of parity on thyroid benign pathology. Recently, parity has been identified as one of the factors contributing to a larger thyroid size in healthy females. The aim of this work was to investigate a possible role for parity on the prevalence of multinodular goiter in iodine deficient areas. For this purpose, the reproductive histories of 2 cohorts of women, normal (Group I, 235 cases) and non-toxic multinodular goiter (NTMNG) affected (Group II, 274 cases) were compared. All subjects were euthyroid and had no previous history of thyroid function abnormalities. The number of full-term previous pregnancies (2.55+/-0.11 vs 1.77+/-0.10) and age (47.7+/-0.76 vs 42.3+/-0.83 yr) were found significantly higher (p<0.001) in multinodular goiter (MNG) patients than controls. Parity and age were found to be directly correlated (p<0.001), nevertheless the partial correlation coefficients demonstrated an independent and statistically significant difference for both variables between normal and NTMNG. Therefore, the independent effects of parity and age were further investigated. The effect of age on NTMNG prevalence seems to be weaker, in fact significant differences (p<0.001) for age between patients and controls were detected only when the effect of parity was absent (nulliparous), while with increasing gestations the effect of age disappeared. Our results indicate that age plays a minor role compared to parity which can therefore be considered as a stronger risk factor. In conclusion, the present study shows that, at least in iodine deficient regions, non-toxic multinodular goiter women show a statistically significant higher parity rate than healthy controls. Age may play a certain role but only when additional stronger risk factors are absent.