Context Ensuring a healthy pregnancy and achieving optimal gestational weight gain (GWG) are important for maternal and child health. Nevertheless, the nutritional advice provided during pregnancy is often conflicting, suggesting limited adherence to clinical practice guidelines (CPGs). Objective The aim of this review was to identify all CPGs on maternal nutrition and GWG and to critically appraise their methodological quality. Data Sources The MEDLINE/PubMed, Cochrane, Guidelines International Network, and BMJ Best Practice databases, along with gray literature, were searched from inception until February 2019 for CPGs and consensus, position, and practice papers. Study Selection Clinical practice guidelines published in English and containing advice on maternal nutrition or GWG were eligible. Data Extraction Two authors independently extracted data on items pertaining to maternal nutrition or GWG, and CPGs were appraised using the AGREE II instrument. Results Twenty-two CPGs were included. All scored adequately in the “scope” domain, but most were considered inadequate with regard to stakeholder involvement, rigor of development, applicability, and editorial independence. Many CPGs lacked patient or dietician involvement, and more than half did not disclose funding sources or conflicts of interest. Guidance on GWG was based mostly on Institute of Medicine thresholds, while nutrition recommendations appeared scattered and heterogeneous. Conclusion Despite the importance of maternal nutrition and the plethora of advising bodies publishing relevant guidance, there is room for substantial improvement in terms of development standards and content of nutritional recommendations. Systematic review registration PROSPERO registration number CRD42019120898.

Iodine deficiency is one of the three key micronutrient deficiencies highlighted as a major public health issue by the World Health Organisation (WHO) and it represents a particular challenge for pregnant women and young children. Indeed, iodine is required for the synthesis of thyroid hormones, which are critical for normal neurodevelopment of the infant. Thus, iodine deficiency has been coined "the most common cause of preventable mental impairment worldwide" (1) . With recent evidence that most UK school-girls are iodine deficient (2) , this study aimed to assess iodine status of women of childbearing age in Scotland, along with habitual intake of iodine-rich foods.Women (n = 381, aged 18-44, median age 30 years, SD 8) were recruited in the West of Scotland from July 2010 to August 2011. A casual spot urine sample was collected, and urinary iodine (UI) was analysed using persulfate digestion followed by Sandel-Kolthoff colorimetric reaction (3) . Iodine status was classified according to the WHO cut-offs, with mild iodine deficiency defined as UI < 100 mg/l, moderate deficiency as UI < 50 mg/l, and severe deficiency as UI < 20 mg/l (4) . Socio-demographic data was collected, and iodine-rich foods consumption was measured using a food frequency questionnaire based on a modified version of an existing questionnaire (5) . The median urinary iodine was 75 mg/l, indicative of mild iodine deficiency; 64 % of the samples had a urinary iodine concentration below 100 mg/l while 31 % of the samples had a urinary iodine concentration below 50 mg/l. Deprivation (SIMD) quintiles were equally represented among the sample. There was no significant difference in urinary iodine concentration between deprivation quintiles, ethnicity, education and income categories, or age categories (18-26 y, 27-35 y and 36-44 y). Multivariate linear regression revealed a strong correlation between urinary iodine and milk intake (r s = 0.15, p < 0.004), but not fish intake.Our results are consistent with data obtained recently UK-wide for girls aged 14-15 (2) . According to the WHO, no more than 20 % of a population should have urinary iodine values below 50 mg/l (4) , but sour sample exceeds this threshold. The absence of iodine prophylaxis in the UK makes women of childbearing age and their future offspring a vulnerable group. With iodine requirement increasing from 140 to 250 mg per day during pregnancy, it is essential that women of childbearing age are provided with sufficient information to make dietary choices ensuring adequate amounts of iodine to cover their needs.