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Kung
Goitrogenesis during pregnancy and neonatal hypothyroxinaemia in a borderline iodine sufficient area.Kung AW, Lao TT, Chau MT, Tam SC, Low LC. Clin Endocrinol (Oxf). 2000 Dec;53(6):725-731. [abstract only]
"OBJECTIVE: Severe iodine deficiency disorders (IDDs) may have been eradicated in many parts of the world, but milder forms still exist and may escape detection. We evaluated the impact of pregnancy on the maternal and fetal thyroid axis in Hong Kong, a coastal city in southern China with borderline iodine intake.
DESIGN: A prospective study performed in a maternity hospital. PATIENTS: Two hundred and thirty pregnant women were prospectively studied and their neonates assessed at birth. MEASUREMENTS: Urine iodine concentration, thyroid function tests and thyroid volume (TV) by ultrasound were determined in the mothers during pregnancy and up to 3 months postpartum and in the neonates.
RESULTS: Increased urinary iodine concentration was seen from first trimester onwards and the proportion of women having urine iodine concentration of < 0.4 micromol/l decreased from 11.3% in the first trimester to 4.7% in the third trimester. There was progressive reduction in circulating fT4 and fT3 concentrations and free thyroxine index (FTI) with increasing gestation and the percentage of women having subnormal levels at term were 53.2%, 61.1% and 4.8%, respectively. The serum TSH concentration during pregnancy doubled towards term. In the first trimester, multiparous women had significantly larger TV than the nulliparous women (P < 0.001). By the third trimester, TV had increased by 30% (range 3-230%) so that the goitre incidence was 14.1%, 21.8%, 25.9% during the three trimesters of pregnancy, and 24.3% and 21.9% at 6 weeks and 3 months postpartum (ANOVA, P < 0.05). The change in thyroid volume during pregnancy correlated positively with the change in thyroglobulin (r = 0.225, P < 0.002) and negatively with urinary iodine concentration (r = - 0.149, P < 0.02). Fourteen women with excessive thyroidal stimulation in the second trimester (defined as those with thyroglobulin (Tg) concentrations in the highest tertile and FTI in the lowest tertile) were found to have lower urine iodine concentrations and larger TV (both P < 0.005) throughout pregnancy, and their neonates had higher cord TSH (P < 0.05), Tg (P < 0.05) and slightly larger TV (P = 0.06) as compared to the findings in 216 pregnant women without evidence of thyroid stimulation. Seven neonates (50%) born to these women had subnormal fT4 levels at birth.
CONCLUSION: In a borderline iodine sufficient area, pregnancy posed an important stress resulting in higher rates of maternal goitrogenesis as well as neonatal hypothyroxinaemia and hyperthyro- trophinaemia. An adequate iodization program is necessary to eliminate iodine deficiency disorders during pregnancy."
Iodine insufficiency and neonatal hyperthyrotropinaemia in Hong Kong.Kung AW, Lao TT, Low LC, Pang RW, Robinson JD. Clin Endocrinol (Oxf). 1997 Mar;46(3):315-9. [abstract only]
"OBJECTIVES: 23% of the neonatal hypothyroidism in Hong Kong is transient. The present study aims to evaluate iodine excretion in healthy pregnant women in Hong Kong and to determine whether iodine insufficiency may occur in the local population to account for the type of neonatal thyroid dysfunction seen in our screening programme.
SUBJECTS: Pilot screening of urinary iodine excretion was determined in 253 healthy pregnant women between 32 and 36 weeks gestation. Fetal and maternal thyroid function in relation to urinary iodine excretion was evaluated in another 55 pregnant women who had given birth to infants with cord blood TSH > or = 16 mIU/I (95th percentile of the cord blood TSH screening programme) and the results were compared to a control group of 160 healthy women whose infants had cord blood TSH < 16 mIU/I.
RESULTS: Using a cut-off value of 0.79 mumol/l, a level as defined by WHO as iodine deficiency, we found that 35.8% of the pregnant women had urinary iodine concentrations below this cut off value. We demonstrated that the existence of borderline iodine supply affected the maternal and fetal thyroid function as evidenced by (i) a negative correlation between maternal TSH and urinary iodine concentration, (ii) higher cord blood TSH in those infants whose mothers had a low urinary iodine concentration as compared to those in whose mothers it was normal, (iii) women who had given birth to infants with cord blood TSH > or = 16 mIU/I had lower urinary iodine concentrations and serum fT4 levels as compared to mothers who had given birth to infants with normal cord TSH levels, and their offspring also had higher cord blood thyroglobulin levels.
CONCLUSION: Although Hong Kong is not a goitrous area, borderline iodine deficiency exists. Iodization of salt in our community could obviate the necessity for iodine supplements in pregnant women and other at-risk groups."
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