Effect of Iodine Nutrition on Pregnancy Outcomes in an Iodine-Sufficient Area in China.

Many studies focused on the association between thyroid disease and pregnancy outcomes. The present study explored the effect of iodine nutrition during the first trimester on pregnancy outcomes. One thousand five hundred sixty-nine pregnant, euthyroid women at ≤12 weeks of gestation in an iodine-sufficient area in China were recruited. According to the World Health Organization (WHO) criteria for iodine nutrition during pregnancy, participants were divided into four groups: adequate iodine (median urinary iodine concentration (UIC), 150-249 µg/L), mild deficiency (UIC, 100-150 µg/L), moderate and severe deficiency (UIC, <100 µg/L), and more than adequate and excessive (UIC, ≥250 µg/L) groups. Pregnancy outcomes, including abortion, gestational hypertension, pre-eclampsia, gestational diabetes mellitus (GDM), placenta previa, placental abruption, preterm labor, low birth weight infants, macrosomia, breech presentation, and cord entanglement, were obtained during follow-up. The results showed that there was no significant difference in general characteristics, including age, body mass index, abdominal circumference, systolic blood pressure, diastolic blood pressure, heart rate, smoking rate, and drinking rate, among the four groups. In the more than adequate and excessive group, thyroid-stimulating hormone (TSH) was greater and free thyroxine (FT4) was lower than any other groups but still within normal range. The thyroglobulin (Tg) level was greater in the moderate and severe deficiency group. The incidence of GDM was significantly greater in women with mild iodine deficiency than in women with adequate iodine nutriture (18.38 vs. 13.70%, p < 0.05). Compared with the adequate group, incidence of macrosomia was significantly greater in the more than adequate and excessive group (12.42 vs. 9.79%, p < 0.05). Mild iodine deficiency was an independent risk factor for GDM (odds ratio = 1.566, 95% confidence interval = 1.060-2.313, p = 0.024); more than adequate and excessive iodine was an independent risk factor for macrosomia (OR = 1.917, CI = 1.128-3.256, p = 0.016). In summary, during 1st trimester, both mild iodine deficiency and excessive iodine intake had adverse impacts on pregnancy outcomes in an iodine-sufficient area.

The Urine Iodine to Creatinine as an Optimal Index of Iodine During Pregnancy in an Iodine Adequate Area in China.

CONTEXT: Iodine nutrition is a global event, especially for pregnant women. OBJECTIVE: To develop applicable index of iodine intake for population during pregnancy. DESIGN, SETTING, AND PARTICIPANTS: From 2012 to 2014, pregnant women at less than 8 weeks of gestation (n = 222) and reproductive-age women (n = 827) participated in this study. The pregnant women were evaluated at follow-up visits at 8, 12, 16, 20, 28, and 36 weeks of gestation and 3 and 6 months postpartum. MAIN OUTCOME MEASURES: Twenty-four-hour urine samples were collected at weeks 8 of gestation. Urine iodine (UI) and creatinine (Cr) and serum thyroglobulin were measured in all of the subjects. Circulatory iodine was measured using inductively coupled plasma-mass spectrometry at 8, 20, and 36 weeks of gestation and 6 months postpartum. RESULTS: The median UI concentration decreased from 183.6 to 104.2 µg/L during pregnancy. The serum iodine (SI) changes were similar to the UI to creatinine ratio (UI/Cr). The SI level was lowest at the eighth week of gestation (60.5 µg/L), which rose significantly until 20 weeks (106.5 µg/L) and then began to decline (36 wk, 84.7 µg/L). The 24-hour UI excretion measurement was regarded as the gold standard. The area under the receiver-operating characteristic curve for UI/Cr was 0.92 for iodine deficiency diagnoses and 0.78 for SI. The area for SI was 0.82 for excessive iodine diagnoses and 0.75 for UI/Cr. The areas under these curves were significantly different (P < .001). The areas under the receiver-operating characteristic curve for UI were 0.61 (P = .11) and 0.65 (P = .08) for iodine deficiency and excessive iodine diagnoses, respectively. Additionally, for thyroglobulin, these values were 0.54 (P = .53) and 0.53 (P = .74), respectively. CONCLUSIONS: Iodine intake, as assessed by spot UI concentration in pregnant women, is inaccurate and increases the prevalence of iodine deficiency. The UI/Cr better reflects the 24-hour iodine excretion and circulating iodine levels during pregnancy and the postpartum period.

Assessment of thyroid function during first-trimester pregnancy: what is the rational upper limit of serum TSH during the first trimester in Chinese pregnant women?

CONTEXT: Guidelines of the American Thyroid Association (ATA) proposed that the upper limit of the TSH reference range should be 2.5 mIU/L in first trimester, but the reported ranges in China are significantly higher. OBJECTIVE: Our objective was to establish a rational reference range of serum TSH for diagnosis of subclinical hypothyroidism in the first trimester of pregnant women in China. DESIGN: We screened 4800 pregnant women in the first trimester and 2000 women who planned to become pregnant and evaluated 535 pregnant women in follow-up visits during the second and third trimester. RESULTS: Median concentrations of serum TSH decreased significantly from the seventh week of gestation. The median of TSH from 4 to 6 weeks was significantly higher than from 7 to 12 weeks (2.15 [0.56-5.31] mIU/L vs 1.47 [0.10-4.34] mIU/L, P<.001); however, there was no significant difference compared with nonpregnant women (2.07 [0.69-5.64] mIU/L; P=.784). The median of free T4 was not significantly altered in the first trimester. The prevalence of subclinical hypothyroidism in the 4800 pregnant women was 27.8% on the diagnostic criteria of TSH>2.5 mIU/L and 4.0% using the reference interval derived by our laboratory (0.14-4.87 mIU/L).Additionally, of 118 pregnant women who had serum TSH>2.5 mIU/L in the first trimester, only 30.0% and 20.3% of them at the 20th and 30th week of gestation had TSH>3.0 mIU/L. CONCLUSIONS: The reference range for nonpregnant women can be used for the assessment of pregnant women at 4 to 6 weeks of gestation. The upper limit of serum TSH in the first trimester was much higher than 2.5 mIU/L in Chinese pregnant women.