Iodine is an essential dietary micronutrient required for thyroid hormone synthesis and neurodevelopment in utero. Evidence of iodine insufficiency among British women is of particular concern in the context of pregnancy. The Mothers and Babies at Yorkhill (MABY) study is a Glasgow-based longitudinal cohort study assessing the iodine and thyroid status of pregnant women and their offspring.
Pregnant women were recruited from antenatal clinics (2015-2016) at gestational week (GW) 28+/-1. Maternal blood and urine samples were collected at GW28, GW36; and from both infant and mother in the first week of life. A validated iodine-specific food frequency questionnaire (FFQ) was completed at GW28 and postnatally. Optional maternal hair and breastmilk samples were also collected postnatally. Maternal and infant urinary iodine status (UI) were determined using the Sandell-Kolthoff method.
Pregnant women (n=710) had a median age of 33 (IQR 30-35). Iodine intake at GW28 (100% FFQ completion) was insufficient at 136μg/day (IQR 101191); or 199μg/day (IQR 121-274) including iodine-containing supplements (used by 40%). At GW28, urine and blood samples were collected from 94% & 94% of participants, and 83% & 78% at GW36, respectively. A total of 609 women gave birth and were followed-up (4% dropout, 5% loss at follow-up, 5% exclusion: early delivery & health issues) together with their singleton infants (54%F:46%M). Postnatal maternal data collection (n=609) was: 99% FFQ, 95% urine, 98% blood, 53% hair and 36% breastmilk. Birthweight was 3535g (IQR 3242-3848) and gestational age 40.1 weeks (IQR 39.3-41.0). Urine and blood spots were obtained from 76% and 89% of infants. Maternal UI was 121μg/L (IQR 61206) at GW28 (n= 574); 121μg/L (IQR 62201) at GW36 (n=503), and 77μg/L (IQR 32166) postnatally (n=580), indicative of iodine insufficiency. Neonatal UI (n=463) was 118μg/L (IQR 71201), with 65% of infants breastfed, 21% formula-fed, and 14% mixed-fed at 5-days of life.
In this population, only 34% of women met the WHO recommendation for iodine intake at GW28, according to FFQ data (food plus supplement intake). Based on maternal UI, the population is iodine insufficient, with only 42% (GW28) and 41% (GW36) above the 150 μg/L WHO pregnancy sufficiency threshold. By contrast, UI was over the 100 μg/L sufficiency threshold in 59% of infants five days postpartum, indicating preferential mother-to-infant iodine transport. Public health strategies are required to counteract iodine insufficiency during pregnancy and should include focus on improving maternal iodine intake during the prenatal period.
19 Sep 2019 - 21 Sep 2019