Thyroid-Stimulating Hormone in Singleton and Twin Pregnancy: Importance of Gestational Age–Specific Reference Ranges

Abstract

Coassolo and colleagues are to be congratulated for building a very large database on women with prior cesarean. 1 This important work and its related findings should help in the difficult task of counseling a patient between a trial of labor and elective repeat cesarean. In their latest publication, 1 they concluded that the risk of uterine rupture was not increased at or beyond 41 weeks of gestation. The rate of uterine rupture in 1,643 women who delivered at or beyond 41 weeks (1.46%) was almost significantly greater than at less than 41 weeks (0.97%) (relative risk 1.51, 95% confidence interval [CI] 0.97-2.36). However, the difference was reduced after adjustment for confounding factors (odds ratio 1.25, 95% CI 0.78 -1.98).These findings are slightly different from ours. 2 We recorded a higher rate of uterine rupture (odds ratio 2.85, 95% CI 1.27-6.42) in women delivering at or beyond 41 weeks of gestation. Due to the smaller size of our study and the rarity of uterine rupture, the CI was very large. It is possible that the real relative risk for uterine rupture at or beyond 41 weeks is closer to 1.5 than 2.9. However, to find such a difference, the calculation of gestational age must be accurate, because inaccuracies will most likely mix the 2 groups (before and after 41 weeks) and reduce the difference between them. In our study, the large majority, if not all, of patients had a first-or second-trimester ultrasound examination for the purpose of dating before 20 weeks of gestation. Although Coassolo et al 1 wrote that women with an unknown or inaccurate gestational age estimate at delivery were excluded; they did not define their method of obtaining an accurate gestational age estimate. We believe that such a study should only include women who underwent antenatal ultrasound before 20 weeks to obtain accu-rate estimated dates of delivery and accurate results.

Thyroid Function Tests During First-trimester of Pregnancy: A Review of Literature

“…w e demonstrate elevated T4 she is really in state o f concluded that the induced elevation of T4 may b e hyperthyroidism but, it is the new physiological condition responsible for the morning sickness, nausea and and the metabolic regulation of pregnant women which vomiting of first-trimester of pregnancy, this finding is in realized and on that base, extra thyroxin requirement is agreement with many other studies in different part of requested, T4 is elevated, not for the sake o f the world (Al-Yatama et al, 2002;Caffrey, 2000; hyperthyroidism, but for the sake growing fetus demand Haddow et al, 2008;Sheehan, 2007). and the maternal new physiological conditions, therefore Laboratory assessment of thyroid function test the establishment of reference intervals and the during early stage of pregnancy and measurement of TSH, methodology of thyroid hormone measurements in each T4,T3,TBG, hCG and thyroid auto-antibodies, all help the region is a great importance (Dash et al, 2005). We argue clinician to properly address a pregnant women with that if the maternal serum thyroxin level, is at normal level hyperthyroidism.…”

Autoimmune Thyroid Disease in Pregnancy: A Review

“…47,49 Of note, it has been reported that the upper 95% Cl for plasma TSH in the first trimester is 2.5 mU=L. 47 It is known that the TSH level descends 60%-80% by week 10 and recovers slowly thereafter, but it may not reach the preconception normal range until gestation ends. 45 …”

“…Interpretation of thyroid function tests should be trimester-specific, 28,47,48 and locally generated trimester-specific reference levels should be applied when available. 47,49 Of note, it has been reported that the upper 95% Cl for plasma TSH in the first trimester is 2.5 mU=L. 47 It is known that the TSH level descends 60%-80% by week 10 and recovers slowly thereafter, but it may not reach the preconception normal range until gestation ends.…”

11 Hypothyroidism in Pregnancy

“…Pregnant women of Moroccan, Turkish or Surinamese descent residing in the Netherlands have TSH values 0.2-0.3 mIU/l lower than Dutch non pregnant women [87]. TSH concentrations are lower in multiple pregnancies since hCG concentrations are higher [88].…”