The Associations Of Urinary Iodine During Pregnancy With Fetal Growth And Birth Outcomes

Objectives: To assess fetal growth characteristics by ultrasonography and examine tracking of fetal growth characteristics during gestation and the relationship between these fetal growth characteristics and adverse birth outcomes;to assess maternal urinary iodine during early pregnancy and further examine the relationship between urinary iodine and fetal growth and birth outcomes.Methods: Participants in the present study were all from the Tongji Maternal and Child Health Cohort(TMCHC).Urine samples were collected during pregnancy for measuring urinary iodine concentration(UIC)and creatinine(Cr)concentrations.Ultrasonic fetal biometry and outcome measurements were collected.The crown-rump length(CRL),head circumference(HC),femur length(FL)and estimated fetal weight(EFW)were evaluated via ultrasonography in each trimester.The birth outcomes included birth HC,FL,length and weight.Tracking was assessed by Pearson correlation and multivariate linear and logistic regression models.We used mixed-effect models and multivariate logistic regression models to assess associations of fetal growth characteristics with adverse birth outcomes.The multiple linear regression model and mixed-effect model were used to examine the association of urinary iodine with fetal growth characteristics and birth outcomes.Results: 1.Among 5886 participants,4569 ultrasound records were taken in the first trimester,4984 in the second trimester and 5404 in the third trimester,and there were 5739 pregnant women having a birth outcome.There were more significant tracking coefficients(correlation coefficient,regression coefficient,odds ratio)between third trimester(HC,FL,EFW)and birth(HC,FL,weight)than between first(CRL)and second(HC,FL,EFW)trimester and birth.These tracking coefficients were not influenced by maternal characteristics and fetal gender.First,second and third trimester fetal growth characteristics were positively associated with risks of small size for gestational age(SGA),and negatively associated with large for gestational age(LGA)at birth(P < 0.05).A one-point increase in growth velocity of HC and FL was associated with decreased risk of preterm birth.2.There were 2087 participants in the study.The median UIC and UIC adjusted by Cr were 178 ?g/L and 234 ?g/gCr,respectively.Of 2087 women,19.8%(n = 414)were with a urine iodine level less than 150 ?g/gCr,and these women could be defined as at risk of iodine deficiency in early pregnancy.About 34.8%(n = 726)had adequate iodine intake(150-249 ?g/gCr),32.1%(n = 669)had iodine intake above the requirements(250-499 ?g/gCr),and 13.3%(n = 278)had excessive iodine intake(?500 ?g/gCr).Compared to the group of adequate iodine intake,the FL in the group of insufficient iodine intake decreased by 0.33 mm(95% CI:-0.63,-0.03,P = 0.029)in second trimester and 0.35 mm(95% CI:-0.66,-0.05,P = 0.023)in third trimester(all P < 0.05),and there was no significant correlation between maternal iodine status and birth HC,FL,length and weight.The mixed-effect models showed thatfetal longitudinal growth in group of maternal insufficient,more than adequate or excessive iodine intake was significantly decreased(all P < 0.05).Conclusions: The ultrasound examination during pregnancy can effectively detect fetal growth characteristics,and most fetal growth characteristics tracked moderately during gestation.Fetal growth characteristics of each trimester can predict the risk of abnormal birthweight,of which increased growth rate can predict low risk of preterm birth.This study population was iodine sufficient during early pregnancy.Maternal iodine insufficiency,more than adequacy and excess adversely affected fetal growth,which increased the risk of adverse birth outcomes.There is an urgent need for ongoing monitoring of iodine status among pregnant women in order to optimize iodine nutrition during pregnancy and avoid undesirable outcomes.