ارتباط بین وضعیت ویتامین D و دیابت بارداری: یک مطالعه مورد- شاهدی

نوع مقاله : اصیل پژوهشی

نویسندگان

1 استادیار گروه زنان و مامایی، دانشکده پزشکی، دانشگاه علوم پزشکی آبادان، آبادان، ایران.

2 دکترای پزشکی، دانشکده پزشکی، دانشگاه علوم پزشکی آبادان، آبادان، ایران.

3 استادیار گروه آمار زیستی، دانشکده پزشکی، دانشگاه علوم پزشکی آبادان، آبادان، ایران.

4 استادیار گروه داخلی، دانشکده پزشکی، دانشگاه علوم پزشکی آبادان، آبادان، ایران.

10.22038/ijogi.2024.74814.5860

چکیده

مقدمه: دیابت بارداری (GDM) از مهم‌ترین علل بروز عوارض در طول بارداری است که شیوع بالایی دارد و شناسایی عوامل مؤثر بر فیزیوپاتولوژی آن به‌عنوان راهکاری جهت پیشگیری و درمان، امری ضروری است، لذا مطالعه حاضر با هدف بررسی سطح سرمی ویتامین D در زنان باردار مبتلا به دیابت بارداری و سالم انجام شد.
روشکار: این مطالعه موردی شاهدی 1402-1401 بر روی 198 زن باردار (99 نفر مبتلا به دیابت بارداری و 99 نفر در گروه شاهد بدون دیابت بارداری) مراجعه کننده به مراکز درمانی دانشگاه علوم پزشکی آبادان انجام گرفت. پس از اخذ رضایت از افراد و ثبت اطلاعات دموگرافیک، سطح سرمی ویتامین D افراد ثبت شد. تجزیه و تحلیل داده­ ها با استفاده از نرم‌افزار آماری SPSS (نسخه 24) و آزمون‌های تی مستقل و آزمون همبستگی پیرسون انجام شد. میزان p کمتر از 05/0 معنی‌دار در نظر گرفته شد.
یافته ­ها: میانگین سطح ویتامین D در زنان دارای GDM به‌صورت معناداری کمتر از زنان باردار گروه شاهد بود (97/16 در مقابل 76/26 نانوگرم بر میلی‌لیتر). با گروه‌بندی زنان باردار بر اساس سن، سن بارداری، گروید و BMI، زنان مبتلا به GDM از میانگین سطح ویتامین D کمتری نسبت به زنان باردار گروه شاهد برخوردار بودند (05/0>p). در بررسی همبستگی در زنان دارای GDM، سطح ویتامین D ارتباط معکوس و معناداری با قند 1 ساعته (212/0- =r، 035/0=p) و قند 2 ساعته (223/0- =r، 026/0=p) داشت، اما ارتباط معناداری با سطح FBS مشاهده نشد. حساسیت و ویژگی ویتامین D در تشخیص GDM در نقطه برش 05/18 برابر با 7/69% و 7/74%، ارزش اخباری مثبت و منفی برابر با 4/73% و 2/71% و دقت کل برابر با 2/72 % بود و میزان توافق نیز در حد متوسط بود.
نتیجه ­گیری: زنان مبتلا به GDM به‌طور قابل توجهی ویتامین D کمتری داشتند که می‌تواند یک عامل خطر برای ابتلاء به GDM در دوران بارداری در نظر گرفته ­شود.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

The relationship between vitamin D status and gestational diabetes mellitus: a case-control study

نویسندگان [English]

  • Somayeh Fallahnezhad 1
  • Aram Bahari 2
  • Bagher Pahlavanzade 3
  • Samaneh Hashemi 4
  • Davood Mosavat 4
1 Assistant professor, Department of Obstetrics and Gynecology, Faculty of Medicine, Abadan University of Medical Sciences, Abadan, Iran.
2 PhD in Medicine, Faculty of Medicine, Abadan University of Medical Sciences, Abadan, Iran.
3 Assistant professor, Department of Biostatistics, Faculty of Medicine, Abadan University of Medical Sciences, Abadan, Iran.
4 Assistant professor, Department of Internal, Faculty of Medicine, Abadan University of Medical Sciences, Abadan, Iran.
چکیده [English]

Introduction: Gestational diabetes (GDM) is one of the most important causes of complications during pregnancy and has a high prevalence, so it is essential to identify the factors affecting its physiopathology as a way to prevent and treat it. Therefore, the present study was performed with aim to investigate the serum level of vitamin D in healthy and diabetic pregnant women.
Methods: This case-control study was conducted in 2022-2023 on 198 pregnant women (99 with gestational diabetes and 99 without gestational diabetes in the control group) referred to the treatment centers of Abadan University of Medical Sciences. After obtaining consent from the subjects and recording demographic information, serum vitamin D levels were also recorded. Data were analyzed by SPSS software (version 24) and Independent T and Pearson correlation tests. P<0.05 was considered statistically significant.
Results: The mean serum level of vitamin D in women with GDM was significantly lower than pregnant women in the control group (16.97 vs. 26.76 ng/ml). By grouping pregnant women based on age, gestational age, gravid and BMI, women with GDM had lower mean vitamin D levels than pregnant women in the control group (P<0.05). In the correlation analysis of women with GDM, vitamin D level had an inverse and significant relationship with 1-hour sugar (r=-0.212 and P=0.035) and 2-hour sugar (r=-0.223 and P=0.026), but no significant relationship with FBS level was observed. The sensitivity and specificity of vitamin D in the diagnosis of GDM at the cut-off point of 18.05 were 69.7% and 74.7%, and the positive and negative predictive value were 73.4% and 71.2%, and the overall accuracy was 72.2% and the level of agreement was moderate.
Conclusion: Women with GDM had significantly less vitamin D, which can be considered a risk factor for GDM during pregnancy.

کلیدواژه‌ها [English]

  • Gestational diabetes
  • Vitamin D
  • Fasting blood sugar
  1. منابع

    1. Atlas D. International diabetes federation. IDF Diabetes Atlas, 7th edn. Brussels, Belgium: International Diabetes Federation 2015; 33(2).
    2. Mohegh S, Taghavi-Ardakani A, Salehi M, Heidari MM, Azadchehr MJ, Etesam Por R, et al. Quality of Life in 6 to 12-Year-Old Children with Overweight and Obesity Compared To Children with Normal Weight. International Journal of Pediatrics 2023; 11(5):17759-68.
    3. Jafari-Shobeiri M, Ghojazadeh M, Azami-Aghdash S, Naghavi-Behzad M, Reza PI, Pourali-Akbar Y, et al. Prevalence and risk factors of gestational diabetes in Iran: a systematic review and meta-analysis. Iranian journal of public health 2015; 44(8):1036.
    4. ACOG Committee Opinion No. 495: Vitamin D: Screening and supplementation during pregnancy. Obstet Gynecol 2011; 118(1):197-198.
    5. Urrutia RP, Thorp JM. Vitamin D in pregnancy: current concepts. Current Opinion in Obstetrics and Gynecology 2012; 24(2):57-64.
    6. Nikooyeh B, Neyestani TR. Oxidative stress, type 2 diabetes and vitamin D: past, present and future. Diabetes/metabolism research and reviews 2016; 32(3):260-7.
    7. Leung PS. The potential protective action of vitamin D in hepatic insulin resistance and pancreatic islet dysfunction in type 2 diabetes mellitus. Nutrients 2016; 8(3):147.
    8. Sung CC, Liao MT, Lu KC, Wu CC. Role of vitamin D in insulin resistance. BioMed Research International 2012; 2012.
    9. Khanh Vinh Quoc Luong KV, Lan Thi Hoang Nguyen LT, Dung Ngoc Pham Nguyen DN. The role of vitamin D in protecting type 1 diabetes mellitus. Diabetes Metab Res Rev 2005; 21(4):338–46.
    10. Dodds L, Woolcott CG, Weiler H, Spencer A, Forest JC, Armson BA, et al. Vitamin D status and gestational diabetes: effect of smoking status during pregnancy. Paediatric and perinatal epidemiology 2016; 30(3):229-37.
    11. Rodriguez A, García‐Esteban R, Basterretxea M, Lertxundi A, Rodríguez‐Bernal C, Iniguez C, et al. Associations of maternal circulating 25‐hydroxyvitamin D3 concentration with pregnancy and birth outcomes. BJOG: An International Journal of Obstetrics & Gynaecology 2015; 122(12):1695-704.
    12. Zhou J, Su L, Liu M, Liu Y, Cao X, Wang Z, et al. Associations between 25-hydroxyvitamin D levels and pregnancy outcomes: a prospective observational study in southern China. European journal of clinical nutrition 2014; 68(8):925-30.
    13. Schneuer FJ, Roberts CL, Guilbert C, Simpson JM, Algert CS, Khambalia AZ, et al. Effects of maternal serum 25-hydroxyvitamin D concentrations in the first trimester on subsequent pregnancy outcomes in an Australian population. The American journal of clinical nutrition 2014; 99(2):287-95.
    14. Fernandez-Alonso AM, Ferrando-Marco P, Dionis-Sanchez EC, Gonzalez-Salmeron MD, Fernandez-Soriano MA, Fiol-Ruiz G, et al. Serum 25-hydroxy-vitamin d levels during the first trimester of pregnancy and perinatal outcomes. J Matern Fetal Neonatal Med. 2010;23:560.
    15. Walsh JM, McGowan CA, Kilbane M, McKenna MJ, McAuliffe FM. The relationship between maternal and fetal vitamin D, insulin resistance, and fetal growth. Reproductive Sciences; 20(5):536-41.
    16. Asemi Z, Hashemi T, Karamali M, Samimi M, Esmaillzadeh A. Effects of vitamin D supplementation on glucose metabolism, lipid concentrations, inflammation, and oxidative stress in gestational diabetes: a double-blind randomized controlled clinical trial. Am J Clin Nutr 2013; 98(6):1425-32.
    17. Asemi Z, Samimi M, Tabassi Z, Shakeri H, Esmaillzadeh A. Vitamin D supplementation affects serum high-sensitivity C-reactive protein, insulin resistance, and biomarkers of oxidative stress in pregnant women. The Journal of nutrition 2013; 143(9):1432-8.
    18. Jamilian M, Karamali M, Taghizadeh M, Sharifi N, Jafari Z, Memarzadeh MR, et al. Vitamin D and evening primrose oil administration improve glycemia and lipid profiles in women with gestational diabetes. Lipids 2016; 51:349-56.
    19. Asemi Z, Karamali M, Esmaillzadeh A. Effects of calcium–vitamin D co-supplementation on glycaemic control, inflammation and oxidative stress in gestational diabetes: a randomised placebo-controlled trial. Diabetologia 2014; 57:1798-806.
    20. Li Q, Xing B. Vitamin D3-supplemented yogurt drink improves insulin resistance and lipid profiles in women with gestational diabetes mellitus: a randomized double blinded clinical trial. Annals of Nutrition and Metabolism 2016; 68(4):285-90.
    21. Samimi M, Kashi M, Foroozanfard F, Karamali M, Bahmani F, Asemi Z, et al. Expression of Concern: The effects of vitamin D plus calcium supplementation on metabolic profiles, biomarkers of inflammation, oxidative stress and pregnancy outcomes in pregnant women at risk for pre‐eclampsia. Journal of human nutrition and dietetics 2016; 29(4):505-15.
    22. Karamali M, Beihaghi E, Mohammadi AA, Asemi Z. Effects of high-dose vitamin D supplementation on metabolic status and pregnancy outcomes in pregnant women at risk for pre-eclampsia. Hormone and Metabolic Research 2015; 47(12):867-72.
    23. Poel YH, Hummel P, Lips PT, Stam F, Van Der Ploeg T, Simsek S. Vitamin D and gestational diabetes: a systematic review and meta-analysis. European journal of internal medicine 2012; 23(5):465-9.
    24. Zhang MX, Pan GT, Guo JF, Li BY, Qin LQ, Zhang ZL. Vitamin D deficiency increases the risk of gestational diabetes mellitus: a meta-analysis of observational studies. Nutrients 2015; 7(10):8366-75.
    25. Lu M, Xu Y, Lv L, Zhang M. Association between vitamin D status and the risk of gestational diabetes mellitus: a meta-analysis. Archives of gynecology and obstetrics 2016; 293:959-66.
    26. Baker AM, Haeri S, Camargo Jr CA, Stuebe AM, Boggess KA. First‐trimester maternal vitamin D status and risk for gestational diabetes (GDM) a nested case‐control study. Diabetes/metabolism research and reviews 2012; 28(2):164-8.
    27. Yap C, Cheung NW, Gunton JE, Athayde N, Munns CF, Duke A, et al. Vitamin D supplementation and the effects on glucose metabolism during pregnancy: a randomized controlled trial. Diabetes care 2014; 37(7):1837-44.
    28. Draznin B, Sussman KE, Eckel RH, Kao M, Yost T, Sherman NA. Possible role of cytosolic free calcium concentrations in mediating insulin resistance of obesity and hyperinsulinemia. The Journal of clinical investigation 1988; 82(6):1848-52.
    29. Alvarez JA, Ashraf A. Role of vitamin D in insulin secretion and insulin sensitivity for glucose homeostasis. International journal of endocrinology 2010; 2010.
    30. Agarwal MM, Dhatt GS, Punnose J, Koster G. Gestational diabetes: dilemma caused by multiple international diagnostic criteria. Diabetic Medicine 2005; 22(12):1731-6.
    31. American Diabetes Association. Standards of medical care in diabetes-2014. Diabetes Care 2014; 37 Suppl 1:S14-80.
    32. Reece EA, Leguizamón G, Wiznitzer A. Gestational diabetes: the need for a common ground. The Lancet 2009; 373(9677):1789-97.
    33. Cashman KD, Dowling KG, Škrabáková Z, Gonzalez-Gross M, Valtueña J, De Henauw S, et al. Vitamin D deficiency in Europe: pandemic?. The American journal of clinical nutrition 2016; 103(4):1033-44.
    34. Zhang C, Qiu C, Hu FB, David RM, van Dam RM, Bralley A, et al. Maternal plasma 25-hydroxyvitamin D concentrations and the risk for gestational diabetes mellitus. PloS one 2008; 3(11):e3753.
    35. Parlea L, Bromberg IL, Feig DS, Vieth R, Merman E, Lipscombe LL. Association between serum 25‐hydroxyvitamin D in early pregnancy and risk of gestational diabetes mellitus. Diabetic medicine 2012; 29(7):e25-32.
    36. Perez-Ferre N, Torrejon MJ, Fuentes M, Fernandez MD, Ramos A, Bordiu E, et al. Association of Low Serum 25-Hydroxyvitamin D Levels in Pregnancy with Glucosehomeostasis and Obstetric And Newborn Outcomes. Endocrine Practice 2012; 18(5):676-84.
    37. Ou WA, Min NI, Hu YY, Zhang K, Wei LI, Fan PI, et al. Association between vitamin D insufficiency and the risk for gestational diabetes mellitus in pregnant Chinese women. Biomedical and Environmental Sciences 2012; 25(4):399-406.
    38. Bener A, Al-Hamaq AO, Saleh NM. Association between vitamin D insufficiency and adverse pregnancy outcome: global comparisons. International journal of women's health 2013: 523-31.
    39. Parildar H, Unal AD, Desteli GA, Cigerli O, Demirag NG. Frequency of Vitamin D deficiency in pregnant diabetics at Baskent University Hospital, Istanbul. Pakistan Journal of Medical Sciences 2013; 29(1):15.
    40. Zuhur SS, Erol RS, Kuzu I, Altuntas Y. The relationship between low maternal serum 25-hydroxyvitamin D levels and gestational diabetes mellitus according to the severity of 25-hydroxyvitamin D deficiency. Clinics 2013; 68:658-64.
    41. Arnold DL, Enquobahrie DA, Qiu C, Huang J, Grote N, VanderStoep A, et al. Early pregnancy maternal vitamin D concentrations and risk of gestational diabetes mellitus. Paediatric and perinatal epidemiology 2015; 29(3):200-10.
    42. Wen J, Hong Q, Zhu L, Xu P, Fu Z, Cui X, et al. Association of maternal serum 25-hydroxyvitamin D concentrations in second and third trimester with risk of gestational diabetes and other pregnancy outcomes. International journal of obesity 2017; 41(4):489-96.
    43. Shahgheibi S, Farhadifar F, Pouya B. The effect of vitamin D supplementation on gestational diabetes in high-risk women: Results from a randomized placebo-controlled trial. Journal of research in medical sciences: the official journal of Isfahan University of Medical Sciences 2016; 21.
    44. Jamilian M, Samimi M, Ebrahimi FA, Hashemi T, Taghizadeh M, Razavi M, et al. The effects of vitamin D and omega-3 fatty acid co-supplementation on glycemic control and lipid concentrations in patients with gestational diabetes. Journal of clinical lipidology 2017; 11(2):459-68.
    45. Maghbooli Z, Hossein‐nezhad A, Karimi F, Shafaei AR, Larijani B. Correlation between vitamin D3 deficiency and insulin resistance in pregnancy. Diabetes/metabolism research and reviews 2008; 24(1):27-32.
    46. Kramer CK, Swaminathan B, Hanley AJ, Connelly PW, Sermer M, Zinman B, et al. Vitamin D and parathyroid hormone status in pregnancy: effect on insulin sensitivity, β-cell function, and gestational diabetes mellitus. The Journal of Clinical Endocrinology & Metabolism 2014; 99(12):4506-13.
    47. Triunfo S, Lanzone A, Lindqvist PG. Low maternal circulating levels of vitamin D as potential determinant in the development of gestational diabetes mellitus. Journal of endocrinological investigation 2017; 40:1049-59.
    48. Xu C, Ma HH, Wang Y. Maternal early pregnancy plasma concentration of 25-hydroxyvitamin D and risk of gestational diabetes mellitus. Calcified tissue international 2018; 102:280-6.
    49. Al-Ajlan A, Al-Musharaf S, Fouda MA, Krishnaswamy S, Wani K, Aljohani NJ, et al. Lower vitamin D levels in Saudi pregnant women are associated with higher risk of developing GDM. BMC pregnancy and childbirth 2018; 18(1):1-7.
    50. Xia J, Song Y, Rawal S, Wu J, Hinkle SN, Tsai MY, et al. Vitamin D status during pregnancy and the risk of gestational diabetes mellitus: a longitudinal study in a multiracial cohort. Diabetes, Obesity and Metabolism 2019; 21(8):1895-905.
    51. Ede G, Keskin U, Cemal Yenen M, Samur G. Lower vitamin D levels during the second trimester are associated with developing gestational diabetes mellitus: an observational cross-sectional study. Gynecological Endocrinology 2019; 35(6):525-8.
    52. Lacroix M, Battista MC, Doyon M, Houde G, Ménard J, Ardilouze JL, et al. Lower vitamin D levels at first trimester are associated with higher risk of developing gestational diabetes mellitus. Acta diabetologica 2014; 51:609-16.
    53. Bal M, Ersoy GŞ, Demirtaş Ö, Kurt S, Taşyurt A. Vitamin D deficiency in pregnancy is not associated with diabetes mellitus development in pregnant women at low risk for gestational diabetes. Turkish journal of obstetrics and gynecology 2016; 13(1):23.
    54. von Websky K, Hasan AA, Reichetzeder C, Tsuprykov O, Hocher B. Impact of vitamin D on pregnancy-related disorders and on offspring outcome. The Journal of steroid biochemistry and molecular biology 2018; 180:51-64.
    55. Shirazian N, Mahboubi M, Roya E, Yousefi-Nooraie R, Fazel-Sarjuei Z, Sedighpour N, et al. Comparison of different diagnostic criteria for gestational diabetes mellitus based on the 75-g oral glucose tolerance test: a cohort study. Endocrine Practice 2008; 14(3):312-7.
    56. Hu L, Zhang Y, Wang X, You L, Xu P, Cui X, et al. Maternal vitamin D status and risk of gestational diabetes: a meta-analysis. Cellular Physiology and Biochemistry 2018; 45(1):291-300.
    57. Clifton‐Bligh RJ, McElduff P, McElduff A. Maternal vitamin D deficiency, ethnicity and gestational diabetes. Diabetic medicine 2008; 25(6):678-84.
    58. Farrant HJ, Krishnaveni GV, Hill JC, Boucher BJ, Fisher DJ, Noonan K, et al. Vitamin D insufficiency is common in Indian mothers but is not associated with gestational diabetes or variation in newborn size. European journal of clinical nutrition 2009; 63(5):646-52.
    59. Soheilykhah S, Mojibian M, Rashidi M, Rahimi‐Saghand S, Jafari F. Maternal vitamin D status in gestational diabetes mellitus. Nutrition in Clinical Practice 2010; 25(5):524-7.
    60. Makgoba M, Nelson SM, Savvidou M, Messow CM, Nicolaides K, Sattar N. First-trimester circulating 25-hydroxyvitamin D levels and development of gestational diabetes mellitus. Diabetes care 2011; 34(5):1091-3.
    61. Savvidou MD, Akolekar R, Samaha RB, Masconi AP, Nicolaides KH. Maternal serum 25‐hydroxyvitamin D levels at 11+ 0–13+ 6 weeks in pregnant women with diabetes mellitus and in those with macrosomic neonates. BJOG: An International Journal of Obstetrics & Gynaecology 2011; 118(8):951-5.
    62. Burris HH, Rifas-Shiman SL, Kleinman K, Litonjua AA, Huh SY, Rich-Edwards JW, et al. Vitamin D deficiency in pregnancy and gestational diabetes mellitus. American journal of obstetrics and gynecology 2012; 207(3):182-e1.
    63. Fernández-Alonso AM, Dionis-Sánchez EC, Chedraui P, González-Salmerón MD, Pérez-López FR. First-trimester maternal serum 25-hydroxyvitamin D3 status and pregnancy outcome. International Journal of Gynecology & Obstetrics 2012; 116(1):6-9.
    64. Park S, Yoon HK, Ryu HM, Han YJ, Lee SW, Park BK, et al. Maternal vitamin D deficiency in early pregnancy is not associated with gestational diabetes mellitus development or pregnancy outcomes in Korean pregnant women in a prospective study. Journal of nutritional science and vitaminology 2014; 60(4):269-75.
    65. Loy SL, Lek N, Yap F, Soh SE, Padmapriya N, Tan KH, et al. Association of maternal vitamin D status with glucose tolerance and caesarean section in a multi-ethnic Asian cohort: the growing up in Singapore towards healthy outcomes study. PloS one 2015; 10(11):e0142239.
    66. Nobles CJ, Markenson G, Chasan-Taber L. Early pregnancy vitamin D status and risk for adverse maternal and infant outcomes in a bi-ethnic cohort: the Behaviors Affecting Baby and You (BABY) Study. British Journal of Nutrition 2015; 114(12):2116-28.
    67. Pleskačová A, Bartáková V, Pácal L, Kuricová K, Bělobrádková J, Tomandl J, et al. Vitamin D status in women with gestational diabetes mellitus during pregnancy and postpartum. BioMed research international 2015; 2015.
    68. Boyle VT, Thorstensen EB, Mourath D, Jones MB, McCowan LM, Kenny LC, et al. The relationship between 25-hydroxyvitamin D concentration in early pregnancy and pregnancy outcomes in a large, prospective cohort. British Journal of Nutrition 2016; 116(8):1409-15.
    69. Tobias DK, Zhang C, Van Dam RM, Bowers K, Hu FB. Physical activity before and during pregnancy and risk of gestational diabetes mellitus: a meta-analysis. Diabetes care 2011; 34(1):223-9.
    70. Prentice A, Goldberg GR, Schoenmakers I. Vitamin D across the lifecycle: physiology and biomarkers. The American journal of clinical nutrition 2008; 88(2):500S-6S.
    71. Thorne‐Lyman AL, Fawzi WW. Vitamin A and carotenoids during pregnancy and maternal, neonatal and infant health outcomes: a systematic review and meta‐analysis. Paediatric and perinatal epidemiology 2012; 26:36-54.
    72. Wacker M, Holick MF. Sunlight and Vitamin D: A global perspective for health. Dermato-endocrinology 2013; 5(1):51-108.
    73. Hollis BW, Wagner CL. Assessment of dietary vitamin D requirements during pregnancy and lactation. The American journal of clinical nutrition 2004; 79(5):717-26.
    74. Lee JM, Smith JR, Philipp BL, Chen TC, Mathieu J, Holick MF. Vitamin D deficiency in a healthy group of mothers and newborn infants. Clinical pediatrics 2007; 46(1):42-4.
    75. Bodnar LM, Simhan HN, Powers RW, Frank MP, Cooperstein E, Roberts JM. High prevalence of vitamin D insufficiency in black and white pregnant women residing in the northern United States and their neonates. The Journal of nutrition 2007; 137(2):447-52.
    76. Aghajafari F, Nagulesapillai T, Ronksley PE, Tough SC, O’Beirne M, Rabi DM. Association between maternal serum 25-hydroxyvitamin D level and pregnancy and neonatal outcomes: systematic review and meta-analysis of observational studies. Bmj 2013; 346.