Nutritional status of iodine in pregnant women in Catalonia (Spain): study on hygiene-dietetic habits and iodine in urine

Iodine is a fundamental micronutrient for the organism which should be regularly administered through foods. Its function is essential for the synthesis of thyroid hormones which in turn act on the different organs and systems of the organism especially in the development of the central nervous system (CNS) from the earliest stages of embryonic and foetal development.

The ingestion of iodine depends on the type of foods consumed, their origin and preparation. Depending on the geographical area, products from the earth may have scarce iodine content. However, foods of marine origin are rich in this micronutrient [1]. In addition, it should be taken into account that foods lose iodine during their preparation: 20% is lost on frying, 23% on baking and 58% on boiling [2]. Some studies have shown that the iodine content of cows' milk differs according to what the animals are fed [3].

All these factors and alimentary habits make it difficult for the daily iodine requirements of the population to be covered through diet. Moreover, iodine is not stored in the body and must therefore be continually replenished. In normal conditions there is equilibrium between iodine intake and urinary elimination, and determination of iodine in urine (ioduria) constitutes a good indicator of iodine intake [4], with assessment of ioduria in a casual urine sample providing adequate information on the nutritional status of iodine [5].

During pregnancy there is an increase in thyroid hormone requirements due to the physiological modifications produced in response to the metabolic demands of pregnancy. This increase can only be achieved by a proportional increase in hormone production which directly depends on the availability of iodine in the diet. Moreover, gestation produces a physiological increase in the elimination of iodine in the urine because of a rise in glomerular filtration. In cases with an underlying deficit in iodine these modifications of pregnancy may not be compensated leading to failure of the mechanisms of adaptation. It is therefore very important to increase iodine intake from the beginning of gestation and even beforehand if possible, similar to the recommendations of supplementation of folic acid. The thyroid hormones available for embryonic and foetal tissue during the first trimester of gestation depend exclusively on maternal hormones and thus, a deficit in maternal iodine can have negative repercussions on prenatal development [6].

According to the World Health Organization (WHO) together with the United Nations International Children's Emergency Fund (UNICEF) and the International Council for Control of Iodine Deficiency Disorders (ICCIDD) the iodine needs of pregnant women have been established as 200 μg/L/day [4]. The ICCIDD has recently raised this recommendation to 250-300 μg/L/day. Maternal iodine intake may be calculated by the determination of ioduria (level of iodine in urine) taking into account that the factor of dilution in urine is greater in pregnant women than in the remaining population. The value of ioduria indicating optimum iodine intake during gestation should be between 150 and 230 μg/L [7]. Studies carried out in different European countries such as France, England, Germany, Switzerland, Ireland and Hungary have demonstrated the highly variable values of iodine deficiency (values less than 150 μg/L) in pregnant women, from 3.5% in England to 57.1% in Hungary [8–13].

Another aspect to consider within hygienic-dietetic habits of pregnant women is smoking and the repercussion this may have on maternal thyroid function. Smoking is considered a goitrogenic substance since it inhibits the absorption of iodine during both gestation and the period of lactation [14]. Smoking during gestation is associated with changes in the levels of thyroid function in both the mother and the foetus. The concentration of Thyroid-stimulating Hormone (TSH) in the mother (in the first and third trimester of gestation) and in the blood of the umbilical cord are lower and the T3 levels are higher which may trigger adverse effects for both [15, 16]. It has also been reported that smoking during the period of lactation increases the risk of iodine deficiency which may lead to brain damage in the lactating child [14].

Iodine deficiency is not only a problem in developing countries but also affects most of the industrialised countries to a greater or lesser degree. It has currently been estimated that half of the population lives in areas in which there is a risk of having disorders due to iodine deficiency such as what occurs in several European countries such as Germany, Belgium, Denmark, Spain, France, Greece, Ireland and Italy. Zones with endemic goitre or some other alterations related to iodine deficiency have been detected in Spain [17–19].

Until several years ago the fundamental problem of iodine deficiency lay in endemic goitre but in the last decades studies have demonstrated a wide spectrum of disorders caused by iodine deficiency during pregnancy such as an increase in the number of abortions and dead foetuses, an increase in neonatal morbimortality and hearing defects in infants [20], a reduction in intellectual capacity and growth, congenital abnormalities with permanent neuromotor damage [21, 22] as well as the attention deficit syndrome and hyperactivity [23, 24]. According to the WHO, lack of iodine is the most frequent cause of mental retardation and irreversible brain lesions in the world [4].

Recent studies have demonstrated that iodine intake during gestation is low, even in areas where theoretically there are institutional prevention programmes to promote the consumption of iodised salt [18, 25–27]. All these studies have been determining factors for the Spanish and the Catalan Societies of Endocrinology and Nutrition, the Spanish Society of Gynaecology and Obstetrics and the Ministry of Health and Social Policies to consider pregnant women as a risk group for disorders as a consequence of iodine deficit and to thereby recommend a diet rich in iodine and iodised supplements. Iodine deficiency in this population, albeit moderate, represents a high risk of cerebral lesions in the foetus [19, 22].

The contribution of the quantity of iodine necessary for a good health status has been included as a basic human right: "All children have the right to an adequate intake of iodine to ensure normal development", especially children yet to be born and thus, "All mothers have the right to adequate iodine ingestion during gestation to ensure that their child achieves an optimum mental development" [28, 29].

Some of the interventions most frequently studied during gestation have been the cessation of smoking and the promotion of maternal breastfeeding. McBride [30] hypothesised that pregnancy may be an "appropriate time for learning" to give up smoking since there is a greater perception of risk in this period and of personal results in pregnancy which provoke affective or strong emotional response and redefines social function or the self-conception of a woman, especially when failure in fulfilment of a social function results in social stigmatisation. This "appropriate time for learning" is not only appropriate for smoking cessation but also for any other health habit of the pregnant woman such as, for example, alimentary habits.

Some studies have demonstrated that the effectiveness of individual versus group Education for Health is similar [31–33] in different populational groups (diabetics, infant asthmatics or pregnant women), while others have reported favourable results in group interventions [34, 35].

The interest in group education has grown in the last years, although very few studies have formally evaluated their effectiveness compared with individual education. In general, group versus individual education carries a reduction in health care costs in hospitalisations, medical consultations and the consumption of drugs for some chronic diseases such as diabetes mellitus and rheumatic diseases as well as different aspects of maternal-foetal health [36].

However, there are numerous difficulties involved in the development of group education such as for example the inadequate or imprecise definition of the educational objectives, the difficulties in evaluating the process and the results as well as the variable attendance of the patients and the limitations in the material and human resources available. Nonetheless, there is sufficient evidence to clearly indicate that these interventions are possible and effective.

The relevance of this study lays not only in knowing the type of educational intervention (group or individual), with modification of alimentary habits in pregnant women being the most effective, but also in performing a follow up of both hygienic-dietetic habits in the consumption of iodine rich foods and ioduria during the three trimesters of gestation. It is particularly of note that in the first trimester, the critical time in embryonic development, midwives in primary care centres should carry out a health care education intervention (individual or group) on these habits with special emphasis on the consumption of foods with high iodine content and iodine supplements.

If the results obtained by this study demonstrate the presence of generalised iodine deficiency during gestation, new studies would be required in other areas of Catalonia and the rest of Spain and would support the need to implement systematic programmes of iodine supplementation during gestation as well as the incorporation of specific educational programmes on alimentary habits.

The hygienic-dietetic habits of a pregnant woman has repercussion on both the nutritional status of the mother and the development and growth of the foetus. According to data obtained in a previous study carried out within the Primary Care setting of Catalonia, there is reduced consumption of foods rich in iodine since 71% report eating fish less than three times per week, 18% do not drink milk daily, only 42% use iodised salt for food condimentation and preparation and 18% of the pregnant women surveyed continue to smoke during gestation. We therefore consider that:

One of the strengths of the present study is its design which is pragmatically oriented with respect to the needs of time and material resources.

Another strength of the study is the large number of midwives and patients involved, reinforcing the external validity of the data.

Since no register of women in the first trimester of pregnancy is available, selection of the study population can not be approached with a simple randomised sample but will rather be performed by consecutive sampling which could lead to a selection bias, the self-selection of the volunteer. To determine the possible presence of such a bias the administrative, sociodemographic and obstetric variables of the women who refuse to participate in the study will be analysed.

To increase the validity and reliability of the data collection of the hygienic-dietetic habits by individualised interview, the midwives have been especially trained in this task following a training session prior to initiation of the pilot study and a support investigator will be available to solve any doubts which may arise.

The difficulty in determining iodine intake through diet will be compensated by the determination of iodine levels in urine which is considered a good marker of iodine ingestion according to the WHO, UNICEF and ICCIDD [4, 45].

To avoid the phenomenon of contamination which may appear when the intervention influences the subjects in the control group (frequent when the same work centre of the professionals belongs to different study groups), randomisation of the intervention will be performed by the PCN and not by study subjects. Although the unit of randomisation is the primary care unit, the intervention is given at the individual level and the outcomes are also measured at this level. The estimation of the design effect will be taken into account in all the main analyses.

Since participant losses and withdrawals randomly occur, any subject exclusion from the analysis may later affect group comparability. To preserve this all the patients included in the study will be evaluated according to the intention to treat principle and thus, all the patients will be analysed as pertaining to the group to which they were initially assigned independently of the treatment they have actually received.

Lastly, it should be pointed out that if the questionnaire on the nutritional status of iodine is found to be valid and reliable, it may be a valuable tool for the detection of iodine deficiency during gestation in midwife consulting offices without the need to request ioduria. The midwife may thereby intervene rapidly and adequately in such a situation informing the woman as to the role of iodine in foetal development and underline the importance of foods rich in iodine.

If the results obtained demonstrate the presence of iodine deficiency in an important proportion of the gestating population, this would support the implementation of preventive interventions to improve and intensify health care education programmes in pregnant women as well as to make the public health authorities aware of the importance and repercussions of iodine deficiency and attempt to systematically implement supplementation of foods containing iodine, a measure which already prevails in some countries such as Argentina.

The IODEGEST Study Group:

PASSIR Sabadell: (Coordination Montse Abella). Nuria Sampedro, Glòria Miralpeix, Montse Villanueva, Concepción Manzano, Judit Cos.

PASSIR Cerdanyola: (Coordination Pilar Soteras). Fermina Casas, Coloma Graells, Mireia Llucià, Rosalia Ibars.

PASSIR Mollet: (Coordination Encarna López). Montserrat Manzanares, Irene Lorente, Eva Artieda, Meritxell Casajoana, Dolors Muñoz, Llucia Burgos, Angelica Hidalgo.

PASSIR Osona: (Coordination Anna Fusté). Dolors Lladó, Rosa Subirats, Angelina Masoliver, Imma Trujillo, Rosa Banús, Dolors Salas, Montse Pujol, Dolors Grau, Roser Sanglas, Anabel Mayos.

PASSIR Bages: (Coordination Náyade Crespo). Rosa Codina, Rosa Forn, Montserrat Galí, Antonia Hidalgo, Teresa Macià, Mercè Vendrell, Montserrat Sallent, Montserrat Ribera, Rosa Oller, Teresa Riba, Esther Romero, Adelaida Expósito, Encarnació Santaeulàlia, Anna Vilaseca.

PASSIR Granollers: (Coordination Dolors Guix). Gemma Olivera, Merche García, Rosa Sans, Marta Roman, Mª Jose Vila, Maite Martinez, Esther Serrano, Sonia Díaz, Carolina Alcaine, Susana Sancho, Remei Fenollosa, Encarna Gascón, Núria Risques, Araceli Santamaria, Remei Corominas, Xavi Espada, Maria Helena Perez, Concepción de la Fuente, Assumpta Prats, Maria Rosa Cabedo, Carme Magem, Mercedes Vigil, Carmen Biern, Montse Bach, Joana Relat.

PASSIR Mútua Terrassa: (Coordination Engracia Coll). Carmen Bayascas, Olga Ezquerro, Patricia Reategui, Anna Campos, Rosa Bach.

PASSIR Anoia: (Coordination Inés Molina). Eva Martinez, Anna Bartolí, Rosa Ferrer, Rocio Hernandez.