A prospective study was undertaken in 87 healthy pregnant women with thyroid antibodies and normal thyroid function at initial presentation [asymptomatic autoimmune thyroid disorders (AITD)]. The aims of the study were to assess whether women with AITD constitute a group at risk of developing subclinical hypothyroidism during pregnancy, and whether a mild thyroid function impairment may be associated with obstetrical repercussions. The women investigated were selected among a cohort of 1660 consecutive pregnancies on the basis of 1) no previous history of thyroid disease, 2) euthyroidism at initial presentation, and 3) positive thyroglobulin antibodies and/or thyroid peroxidase antibodies (TPO-Ab). Women with AITD had a basal TSH value significantly higher, albeit still normal, in the first trimester (1.6 vs. 0.9 mU/L; P < 0.001) than that in women with healthy pregnancies used as controls. Despite a 60% average reduction in TPO-Ab titers during gestation, serum TSH remained higher in women with AITD than in controls throughout gestation: at delivery, 40% of the cases had serum TSH levels above 3 mU/L, and 16% had serum TSH levels above 4 mU/L. A TRH test carried out in the days after parturition showed an exaggerated response in 50% of the cases. Furthermore, free T4 concentrations were in the range of hypothyroid values in 42% of the women. Obstetrical repercussions were observed, namely increased rates of spontaneous miscarriage and premature deliveries. In conclusion, women with asymptomatic AITD who are euthyroid in early pregnancy carry a significant risk of developing hypothyroidism progressively during gestation, despite a marked reduction in antibody titers. Hypothyroidism results from the reduced ability of the gland to adjust to the changes in thyroidal economy associated with pregnancy. At the individual level, progression to subclinical hypothyroidism was broadly predictable on the basis of serum TSH levels and TPO-Ab titers in the first trimester. Hence, these parameters provide useful markers to identify women who carry a higher risk, allowing for a close monitoring of thyroid function during pregnancy and the administration of L-T4 in specific cases. Taken together with the known incidences of postpartum thyroiditis and hypothyroidism in women with AITD, the present observations in our opinion justify systematic screening of thyroid autoimmunity during pregnancy.
Public health strategies and preventive policies should be focused on more common human risk factors such as disregarding traffic rules and regulations, drivers' rushing, and alcohol consumption due to their greater population attributable fraction and more intuitive impacts on society.
Normal moveout (NMO) correction is routinely applied to traces of each common-midpoint (CMP) gather before forming a stack section. Conventional NMO correction has the drawback of producing stretching as a natural result of convergence of the NMO trajectories. Although this problem exists on completely hyperbolic reflections, the reflections will be further deviated from the desirable zero-offset equivalent if they indicate nonhyperbolic behavior. We have addressed this issue and developed a new method of stretch-free NMO correction in two steps: first, a novel way of rectifying NMO correction trajectories in a shifted hyperbolic NMO base, and second, a prioritized successive process of mapping data samples into an NMO-corrected gather. We have determined the advantage of the proposed method over two preceding methods: isomoveout and local stretch zeroing. The effectiveness of the new method in producing a stretch-free NMO gather was tested on synthetic data generated by ray tracing and a real data set of 200 CMP gathers of an Iranian oil field. The proposed method can be used in the presence of hyperbolic and nonhyperbolic events, and it recovers the amplitudes of interfering reflections to extend the usable offsets.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.