Abstract
BackgroundThe relationship between congenital hypothyroidism (CH) and multiple pregnancy has not been fully studied in Japan.MethodsComplete nationwide data of assisted reproductive technology (ART) in Japan from 2005 to 2009 presented by the Japan Society of Obstetrics and Gynecology, which include information on CH and birth defects were used for analyses. Diseases were reclassified according to the International Classification of Diseases, tenth edition (ICD-10, 2003 version). The relative risk (RR) and 95% confidence interval (CI) of the incidence rate for CH was calculated with singletons as the reference group. Additional birth defects with CH were examined. The probandwise concordance rate of multiples and recurrence risk ratio were calculated.ResultsThere were 18 patients with CH, consisting of 12 singletons and 6 multiples. The incidence rates of CH per 1,000 live births in singletons and multiples are 0.14 (=12/87,145) and 0.31 (=6/19,533), respectively. The incidence rate was more than twofold higher in multiple births than in singleton births, but the difference was not statistically significant (RR=2.2, 95% CI 0.8–5.9). Additional birth defects were present in three patients with CH (17%=3/18). The multiples were affected by other birth defects more frequently (33%=2/6) than the singletons (8%=1/12). The six multiple-births patients were derived from one concordant twin pair, which consisted of two twin patients; three discordant twin pairs, which consisted of three twin patients; and one discordant triplets set, which consisted of one triplet patient. Thus, the probandwise concordance rate was 33.3% (=2/(2+4)). The estimated recurrence risk ratio was 1976 (for the total ART population) or 609 (for the Japanese general population).ConclusionsCH was more frequent in multiples compared to singletons. A higher percentage of additional birth defects was also observed in multiples compared to singletons. The familial aggregation of CH was suggested.
Highlights
The relationship between congenital hypothyroidism (CH) and multiple pregnancy has not been fully studied in Japan
Another population-based study in the U.S showed that the incidence rates of CH in twins doubled as compared to that in singletons, and the incidence rate was even higher with triplets/+ [6]
Many studies reported a higher incidence rate of extrathyroidal additional birth defects among neonates with CH compared with the general population [8,12,13,14,15,16,17,18,19,20,21,22,23,24], especially congenital heart disease [8,14,17,21,22,23,24,25]
Summary
The relationship between congenital hypothyroidism (CH) and multiple pregnancy has not been fully studied in Japan. Using the same CH registry, Olivieri et al [11] showed that the incidence rate of CH in multiples was more than 3-fold higher compared to singletons. Many studies reported a higher incidence rate of extrathyroidal additional birth defects among neonates with CH compared with the general population [8,12,13,14,15,16,17,18,19,20,21,22,23,24], especially congenital heart disease [8,14,17,21,22,23,24,25]
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