Selenium supplementation and premature (pre-labour) rupture of membranes: a randomised double-blind placebo-controlled trial

The effect of selenium supplementation in pregnant women on maternal, fetal, and newborn outcomes: a systematic review and meta-analysis

OBJECTIVE

Low maternal selenium status has been associated with poor pregnancy outcomes, including preterm birth. This study aimed to evaluate available evidence of the effects of selenium supplementation during pregnancy on preterm birth and related maternal, fetal, and newborn outcomes.

DATA SOURCES

MEDLINE, Embase, CINAHL, Global Index Medicus, and the Cochrane Library were systematically searched on June 23, 2022, without language or time restrictions.

STUDY ELIGIBILITY CRITERIA

Randomized controlled trials and nonrandomized interventional studies were included if they compared the effects of selenium supplementation with placebo or no treatment among pregnant women. The review protocol was registered in the International Prospective Register of Systematic Reviews (identification number: CRD42022383669).

METHODS

For outcomes reported by ≥1 study, a meta-analysis was conducted. Because of the small number of studies and high clinical heterogeneity between populations, random-effects models were used. The Risk of Bias 2 and Risk Of Bias In Non-randomized Studies - of Interventions tools were used to assess study quality, and Grading of Recommendations Assessment, Development, and Evaluation analysis was used to determine the certainty of evidence for each outcome.

RESULTS

Literature searches identified 5105 unique records, and 32 studies met the eligibility criteria. Of note, 11 reports were not included for analysis following research integrity assessments. Moreover, 10 trials and 3 observational studies met the inclusion criteria; however, only 8 trials (1851 women) and 1 prospective cohort study (71,728 women) reported on at least 1 review outcome. Our results could not determine the effect of selenium supplementation on preterm birth at <37 weeks of gestation (relative risk, 0.65; 95% confidence interval, 0.26-1.63; very low certainty evidence) and <34 weeks of gestation (relative risk, 1.05; 95% confidence interval, 0.59-1.44; very low certainty evidence).

CONCLUSION

There is limited evidence on the effects of selenium supplementation during pregnancy. Further trials, with larger sample sizes, more representative populations, and reliable assessment of maternal selenium status at trial entry, are required.

Effects of selenium levels on placental oxidative stress and inflammation during pregnancy: a prospective cohort study

BACKGROUND

Studies on the impact of Se levels in different pregnancy periods on placental function are limited.

AIM

This cohort study sought to investigate the levels of the trace element Se and to assess their effects on placental oxidative stress (OS) and mRNA expression of inflammatory genes during pregnancy.

METHODS

The study population consisted of 2519 pregnant women from the Ma'anshan birth cohort. Se levels were measured in the first and second trimesters of pregnancy and in cord blood using inductively coupled plasma-mass spectrometry (ICP-MS). Placental stress and mRNA expression of inflammatory genes were assessed using RT-PCR.

RESULTS

A statistically significant negative association was noted between Se levels in the second trimester of pregnancy and mRNA expression of placental HO-1(β = -0.009, p < .01), HIF1α (β = -0.005, p = .010), GRP78 (β = -0.011, p < .001), CRP (β = -.007, p = .033) and CD68 (β = -0.006, p = .019). A negative association was noted between Se levels in cord blood and mRNA expression of placental HO-1 (β = -0.007, p = .004), HIF1α (β = -0.006, p = .005) and GRP78 (β = -0.009, p = .004). We found that prenatal Se status was associated with placental stress and mRNA expression of inflammatory genes.

CONCLUSION

Se deficiency during pregnancy, especially in the second trimester, leads to the production of OS and an increase in inflammatory mediators, affecting the growth and development of the fetus. Monitoring of pregnant women's nutritional status is necessary to prevent nutritional imbalances and deficiencies in important micronutrients in the fetal.

Selenium Supplementation in Pregnancy-Maternal and Newborn Outcomes

Background. Several studies have suggested that increased oxidative stress during pregnancy may be associated with adverse maternal and foetal outcomes. As selenium is an essential mineral with an antioxidant role, our aim was to perform a systematic review of the existing literature reporting the effects of selenium supplementation during pregnancy on maternal and neonatal outcomes. Materials and Methods. Six electronic databases (Medline, Embase, Cochrane Library, Web of Science, Scopus, and PubMed) were searched for studies reporting the effects of selenium supplementation during pregnancy and the postpartum period on maternal and neonatal outcomes. Only randomised controlled trials on human subjects reported in English and published up to October 2021 were included. Quality assessments were conducted using the modified Downs and Black quality assessment tool. Data were extracted using a narrative synthesis. Results. Twenty-two articles were included in our systematic review (seventeen reported on maternal outcomes, two on newborn outcomes, and three on both). Maternal studies reported the effects of selenium supplementation in the prevention of thyroid dysfunction, gestational diabetes, pregnancy-induced hypertension/preeclampsia, oxidative stress, postpartum depression, premature rupture of membranes, intrauterine growth retardation, breastmilk composition, and HIV-positive women. Newborn studies reported the effects of maternal selenium supplementation on foetal oxidation stress, foetal lipid profile, neonatal hyperbilirubinemia, and newborn outcomes in HIV-positive mothers. The majority of studies were inappropriately designed to establish clinical or scientific utility. Of interest, four studies reported that selenium supplementation reduced the incidence of thyroid dysfunction and permanent hypothyroidism during the postpartum period by reducing thyroid peroxidase and thyroglobulin antibody titres. Conclusion. The evidence supporting selenium supplementation during pregnancy is poor and there is a need for appropriately designed randomised controlled trials before routine use can be recommended.

In vitro selenium supplementation suppresses key mediators involved in myometrial activation and rupture of fetal membranes

Spontaneous preterm birth, which can affect up to 20% of all pregnancies, is the greatest contributor to perinatal morbidity and mortality. Infection is the leading pathological cause of spontaneous preterm birth. Infection activates the maternal immune system, resulting in the upregulation of pro-inflammatory and pro-labor mediators that activate myometrial contractions and rupture of fetal membranes. Anti-inflammatory agents therefore have the potential for the prevention of spontaneous preterm birth. Selenium, an essential micronutrient, has been shown to be a potent anti-inflammatory regulator. Notably, clinical and epidemiological studies have suggested a link between selenium and preterm birth. Thus, the aim of this study was to assess the effect of selenite (an inorganic form of selenium) on the expression of pro-inflammatory and pro-labor mediators in human gestational tissues. Human fetal membranes and myometrium were pre-incubated with or without selenite before incubation with the bacterial product lipopolysaccharide (LPS) to stimulate inflammation associated with preterm birth. Selenite blocked LPS-induced expression of pro-inflammatory cytokines and chemokines and enzymes involved in remodelling of myometrium and degradation of fetal membranes. Of note, selenite also suppressed myometrial activation induced by inflammation as evidenced by a decrease in LPS-induced prostaglandin signalling and myometrial cell contractility. These effects of selenite were mediated by the MAPK protein ERK as selenite blunted LPS induced activation of ERK. In conclusion, selenite suppresses key mediators involved in inflammation induced activation of mediators involved in active labor in human fetal membranes and myometrium. These findings support recent clinical studies demonstrating selenium supplementation is associated with decreased incidence of spontaneous preterm birth.

Effect of Iodine and Selenium on Proliferation, Viability, and Oxidative Stress in HTR-8/SVneo Placental Cells

Adequate maternal micronutrition is vital for placental formation, fetal growth, and development. Oxidative stress adversely affects placental development and function and an association between deficient placental development, oxidative stress, and micronutrient deficiency has been observed. Selenium and iodine are two essential micronutrients with antioxidant properties. Epidemiological studies have shown that poor micronutrient status in pregnant women is associated with a higher incidence of pregnancy complications. The aim of this study was to determine how selenium, iodine, and their combination impact oxidative stress in placental trophoblast cells. HTR8/SVneo extravillous trophoblasts were supplemented with a concentration range of organic and inorganic selenium, potassium iodide, or their combination for 24 h. Oxidative stress was then induced by treating cells with menadione or H₂O₂ for 24 h. Cell viability and lipid peroxidation as the biomarker of oxidative stress were assessed at 48 h. Both menadione and H₂O₂ reduced cell viability and increased lipid peroxidation (P < 0.05). Greater cell viability was found in selenium-supplemented cells when compared with vehicle treated cells (P < 0.05). Selenium and iodine supplementation separately or together were associated with lower lipid peroxidation compared with vehicle control (P < 0.05). Supplementation with the combination of selenium and iodine resulted in a greater reduction in lipid peroxidation compared with selenium or iodine alone (P < 0.05). Oxidative stress negatively impacts trophoblast cell survival and cellular integrity. Selenium and iodine protect placental trophoblasts against oxidative stress. Further research is warranted to investigate the molecular mechanisms by which selenium and iodine act in the human placenta.

Effect of Selenium and Iodine on Oxidative Stress in the First Trimester Human Placenta Explants

Imbalanced maternal micronutrient status, poor placentation, and oxidative stress are associated with greater risk of pregnancy complications, which impact mother and offspring health. As selenium, iodine, and copper are essential micronutrients with key roles in antioxidant systems, this study investigated their potential protective effects on placenta against oxidative stress. First trimester human placenta explants were treated with different concentrations of selenium (sodium selenite), iodine (potassium iodide), their combination or copper (copper (II) sulfate). The concentrations represented deficient, physiological, or super physiological levels. Oxidative stress was induced by menadione or antimycin. Placenta explants were collected, fixed, processed, and embedded for laser ablation inductively coupled plasma-mass spectrometry (LA ICP-MS) element imaging or immunohistochemical labelling. LA ICP-MS showed that placenta could uptake selenium and copper from the media. Sodium selenite and potassium iodide reduced DNA damage and apoptosis (p < 0.05). Following oxidative stress induction, a higher concentration of sodium selenite (1.6 µM) was needed to reduce DNA damage and apoptosis while both concentrations of potassium iodide (0.5 and 1 µM) were protective (p < 0.05). A high concentration of copper (40 µM) increased apoptosis and DNA damage but this effect was no longer significant after induction of oxidative stress. Micronutrients supplementation can increase their content within the placenta and an optimal maternal micronutrient level is essential for placenta health.

Effects of selenium supplementation on pregnancy outcomes and disease progression in HIV-infected pregnant women in Lagos: A randomized controlled trial

OBJECTIVE

To examine the effects of selenium supplementation on pregnancy outcomes and disease progression among HIV-infected pregnant women in Lagos.

METHODS

A randomized, placebo-controlled trial conducted among HIV-positive pregnant women between September 2018 and August 2019. At enrollment, 90 women were randomly assigned into each treatment arm to receive either a daily tablet of 200 μg elemental selenium or a placebo. Relevant participants' sociodemographic and clinical data were collected at enrollment and delivery.

RESULTS

Women in the selenium arm had a significantly lower risk of preterm delivery (relative risk [RR] 0.32, 95% confidence interval [CI] 0.11-0.96) and a non-significant reduction in the risk of delivering term neonates with a low delivery weight (RR 0.24, 95% CI 0.05-1.19). Supplemental selenium does not increase the risk of perinatal death and adverse drug events.

CONCLUSION

The study reported a beneficial effect of prenatal selenium supplements on the risk of preterm delivery with no further reduction in risk among HIV-infected women who used the supplements for more than 14 weeks.

TRIAL REGISTRATION

Pan African Clinical Trial Registry (PACTR201809756724274).

Low Selenium Levels in Amniotic Fluid Correlate with Small-For-Gestational Age Newborns

Background: Identifying women at risk for small-for-gestational-age newborns (SGA) is an important challenge in obstetrics. Several different risk factors have been suggested to contribute to the development of SGA. Previous research is inconclusive on the role selenium (Se) plays in the development of SGA. The aim of the study was therefore to explore the role of Se concentrations in amniotic fluid in order to understand its possible role in the development of SGA. Study Design: This prospective, single center study investigated the relationships between Se concentrations in amniotic fluid and pregnancy outcomes. Amniotic fluid was collected from pregnant women during amniocentesis at 16/17 weeks of pregnancy. Se values were determined using the electrothermal atomic absorption spectrometry and expressed in µg/L. Characteristics of mothers and newborns were obtained from women and delivery records. Results: 327 samples of amniotic fluid were evaluated. Patients with SGA newborns had significantly lower mean values of amniotic fluid concentrations of Se compared to appropriate-for-gestational-age (AGA) newborns (4.8 ± 1.9 µg/L versus 5.6 ± 2.5 µg/L (p = 0.017)). Adjusting for different risk factors, Se remained the only significant factor impacting the outcome of a newborn (b = −0.152, s.e. = 0.077; p < 0.048). Se levels in amniotic fluid did not correlate with pre-eclampsia or preterm delivery. Conclusion: Amniotic fluid Se levels represent a viable root of further investigation and assessment in order to identify women with low birth weight newborns early. Women with decreased Se levels had a statistically significant chance of developing SGA. Further research is needed to elucidate the link between Se, other trace elements, and other risk factors and their impact on the development of SGA newborns.

A Review of the Potential Interaction of Selenium and Iodine on Placental and Child Health

A healthy pregnancy is important for the growth and development of a baby. An adverse pregnancy outcome is associated with increased chronic disease risk for the mother and offspring. An optimal diet both before and during pregnancy is essential to support the health of the mother and offspring. A key mediator of the effect of maternal nutrition factors on pregnancy outcomes is the placenta. Complicated pregnancies are characterized by increased oxidative stress in the placenta. Selenium and iodine are micronutrients that are involved in oxidative stress in placental cells. To date, there has been no comprehensive review investigating the potential synergistic effect of iodine and selenium in the placenta and how maternal deficiencies may be associated with increased oxidative stress and hence adverse pregnancy outcomes. We undertook a hypothesis-generating review on selenium and iodine, to look at how they may relate to pregnancy complications through oxidative stress. We propose how they may work together to impact pregnancy and placental health and explore how deficiencies in these micronutrients during pregnancy may impact the future health of offspring.

Pregnancy, thyroid, and the potential use of selenium

The management of pregnant women is a major concern of health care around the world. There is growing evidence regarding the influence of selenium (Se) on pregnancy and fetus outcomes. However, due to as yet insufficient evidence, lack of measurable markers to assess the effect of Se supplementation on the human metabolism, and Se's narrow therapeutic index, the majority of experts and the current guidelines published by several scientific societies do not recommend the use of Se in pregnancy and in women of childbearing age. Further research based on well-designed studies, including assessment of the complex interactions between different micronutrients and individual response to different doses of Se, is needed.

Selenium and Health: An Update on the Situation in the Middle East and North Africa

Selenium (Se) is an important trace element that should be present in the diet of all age groups to provide an adequate intake. Se is incorporated in 25 known selenoproteins, which mediate the biological effects of Se including, immune response regulation, maintenance of thyroid function, antioxidant defense, and anti-inflammatory actions. A balanced intake of Se is critical to achieve health benefits because depending on its status, Se has been found to play physiological roles or contribute to the pathophysiology of various diseases including, neurodegenerative diseases, diabetes, cancer, and cardiovascular disorders. Se status and intake are very important to be known for a specific population as the levels of Se are highly variable among different populations and regions. In the Middle East and North African (MENA) region, very little is known about the status of Se. Studies available show that Se status is widely variable with some countries being deficient, some over sufficient, and some sufficient. This variability was apparent even within the same country between regions. In this review, we summarized the key roles of Se in health and disease and discussed the available data on Se status and intake among countries of the MENA region.

A review of dietary selenium intake and selenium status in Europe and the Middle East

This is a systematic review of existing data on dietary selenium (Se) intake and status for various population groups in Europe (including the United Kingdom (UK)) and the Middle East. It includes English language systematic reviews, meta-analyses, randomised controlled trials, cohort studies, cross-sectional and case-control studies obtained through PUBMED searches from January, 2002, to November, 2014, for European data and from 1990 to November 2014, for Middle Eastern data. Reports were selected if they included data on Se intake and status. The search identified 19 European/UK studies and 15 investigations in the Middle East that reported Se intake and Se concentration in water and/or food and 48 European/UK studies and 44 investigations in the Middle East reporting Se status. Suboptimal Se status was reported to be widespread throughout Europe, the UK and the Middle East, and these results agreed with previous reports highlighting the problem. Eastern European countries had lower Se intake than Western European countries. Middle Eastern studies provided varying results, possibly due to varying food habits and imports in different regions and within differing socioeconomic groups. In conclusion, Se intake and status is suboptimal in European and Middle Eastern countries, with less consistency in the Middle East.

Reduced serum selenium concentration in miscarriage incidence of Indonesian subjects

Selenium is an essential nutrient for human health, and maternal selenium concentration has been reported to be associated with pregnancy outcome. To further investigate the possible role of selenium (Se) in miscarriage, we conducted a case-control study to evaluate the correlations among selenium status, glutathione peroxidase activity, and spontaneous abortion. A total of 46 subjects with normal pregnancies and 25 subjects with spontaneous abortion were recruited, and their serum selenium concentrations and serum glutathione peroxidase activities were analyzed. The total serum selenium concentrations in subjects with normal pregnancies were significantly higher than those of subjects with spontaneous abortion; however, the glutathione peroxidase activities were similar in both groups. We further separated the subjects into smoking and nonsmoking groups, and the logistic regression analysis suggested that total serum selenium concentration, but not serum glutathione peroxidase activity or smoking, was significantly correlated with the incidence of miscarriage. The present study thus reaffirms that low serum selenium levels are associated with miscarriage and that selenium plays an important role in pregnancy maintenance.

Dietary selenium and selenoprotein function

Selenium is a trace mineral and an essential nutrient in the human diet. Selenium is found in soil and water and consequently enters the food chain through the root ways of plants and aquatic organisms. Some areas of the world are low in soil selenium resulting in a selenium deficient population and the appearance of an associated heart disease and bone disorders that can be corrected with dietary selenium. Indeed the requirement for dietary selenium was established by these observations and while selenium deficiency is rare in the West, patients requiring long-term intravenous feedings have also show heart disease associated with a deficiency of selenium in the feeding fluids. Subsequently, it has been established that dietary selenium can improve a wide range of human health conditions even in areas with soil replete in selenium.

Selenium in reproductive health

Selenium is an essential trace element of importance to human biology and health. Increasing evidence suggests that this mineral plays an important role in normal growth and reproduction in animals and humans, and selenium supplementation is now recommended as part of public health policy in geographical areas with severe selenium deficiency in soil. This review addresses the biological functions of selenium followed by a detailed review of associations between selenium status and reproductive health. In many countries, selenium dietary intake falls below the recommended nutrient intakes and is inadequate to support maximal expression of the selenoenzymes. Numerous reports implicate selenium deficiency in several reproductive and obstetric complications including male and female infertility, miscarriage, preeclampsia, fetal growth restriction, preterm labor, gestational diabetes, and obstetric cholestasis. Currently, there is inadequate information from the available small intervention studies to inform public health strategies. Larger intervention trials are required to reinforce or refute a beneficial role of selenium supplementation in disorders of reproductive health.

The importance of antioxidant micronutrients in pregnancy

Pregnancy places increased demands on the mother to provide adequate nutrition to the growing conceptus. A number of micronutrients function as essential cofactors for or themselves acting as antioxidants. Oxidative stress is generated during normal placental development; however, when supply of antioxidant micronutrients is limited, exaggerated oxidative stress within both the placenta and maternal circulation occurs, resulting in adverse pregnancy outcomes. The present paper summarises the current understanding of selected micronutrient antioxidants selenium, copper, zinc, manganese, and vitamins C and E in pregnancy. To summarise antioxidant activity of selenium is via its incorporation into the glutathione peroxidase enzymes, levels of which have been shown to be reduced in miscarriage and preeclampsia. Copper, zinc, and manganese are all essential cofactors for superoxide dismutases, which has reduced activity in pathological pregnancy. Larger intervention trials are required to reinforce or refute a beneficial role of micronutrient supplementation in disorders of pregnancies.

Selenium and preeclampsia: A global perspective

Preeclampsia is a complex multisystem disorder of pregnancy where oxidative stress plays an important aetiological role. The role of selenium in the synthesis of endogenous antioxidants is well documented, and a significant reduction in selenium has been reported in preeclamptic women. The objective of this study was to map global selenium status and preeclampsia incidence. This study identified peer reviewed journal articles reporting national preeclampsia incidence (%) and matched these with reported values of selenium intake and plasma/serum selenium concentrations (μg/L). Matched data were obtained for 45 regions, reporting 6456,570 births, spanning Europe, Asia, Australasia, Africa, North and South America. Increasing plasma selenium concentration was found to be correlated with a reduction in preeclampsia incidence (Pearson's r=-0.604, P<0.0001). Countries with a reported serum/plasma selenium level of ⩾95μg/L were considered selenium sufficient and a significant reduction in preeclampsia incidence for countries above this value (P=0.0007) was noted. Significant reductions in preeclampsia incidence were found to coincide with increases in plasma/serum selenium concentration in the New Zealand (P=0.0003) and Finland (0.0028) populations following Government intervention. This study supports the hypothesis that selenium supplementation may be beneficial in reducing oxidative stress in women at risk of preeclampsia.

Maternal selenium status during early gestation and risk for preterm birth

BACKGROUND

Preterm birth occurs in 5%-13% of pregnancies. It is a leading cause of perinatal mortality and morbidity and has adverse long-term consequences for the health of the child. Because of the role selenium plays in attenuating inflammation, and because low concentrations of selenium have been found in women with preeclampsia, we hypothesized that low maternal selenium status during early gestation would increase the risk of preterm birth.

METHODS

White Dutch women with a singleton pregnancy (n = 1197) were followed prospectively from 12 weeks' gestation. Women with thyroid disease or type 1 diabetes were excluded. At delivery, 1129 women had complete birth-outcome data. Serum concentrations of selenium were measured during the 12th week of pregnancy. Deliveries were classified as preterm or term, and preterm births were subcategorized as iatrogenic, spontaneous or the result of premature rupture of the membranes.

RESULTS

Of the 60 women (5.3%) who had a preterm birth, 21 had premature rupture of the membranes and 13 had preeclampsia. The serum selenium concentration at 12 weeks' gestation was significantly lower among women who had a preterm birth than among those who delivered at term (mean 0.96 [standard deviation (SD) 0.14] μmol/L v. 1.02 [SD 0.13] μmol/L; t = 2.9, p = 0.001). Women were grouped by quartile of serum selenium concentration at 12 weeks' gestation. The number of women who had a preterm birth significantly differed by quartile (χ² = 8.01, 3 degrees of freedom], p < 0.05). Women in the lowest quartile of serum selenium had twice the risk of preterm birth as women in the upper three quartiles, even after adjustment for the occurrence of preeclampsia (adjusted odds ratio 2.18, 95% confidence interval 1.25-3.77).

INTERPRETATION

Having low serum selenium at the end of the first trimester was related to preterm birth and was independent of the mother having preeclampsia. Low maternal selenium status during early gestation may increase the risk of preterm premature rupture of the membranes, which is a major cause of preterm birth.