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ORIGINAL RESEARCH COMMUNICATION |
1 From the Department of Epidemiology, Institute of Public Health, University of Copenhagen (HF); the Blair Research Laboratory, Ministry of Health, Harare, Zimbabwe (EG); the Department of Immunology, University of Zimbabwe, Harare, Zimbabwe (EG); the Department of Clinical Pharmacology, University of Zimbabwe, Harare, Zimbabwe (NN); the Department of Medical Laboratory Sciences, University of Zimbabwe, Harare, Zimbabwe (PN); the Department of Clinical Biochemistry, Aalborg University Hospital, Aalborg, Denmark (HK); and the Department of Human Nutrition, Royal Veterinary and Agricultural University, Frederiksberg, Denmark (PK and KFM)
2 Supported by the Council for Development Research, Danish International Development Assistance (to HF); the Danish Council for Medical Research (to HF); Southampton Insurance, Zimbabwe; the Foundation of 1870; BASF Health and Nutrition; the Hørslev Foundation; the Dagmar Marshall Foundation; the Sophus Jacobsens Foundation; and the Lily Benthine Lunds Foundation.
3 Address reprint requests to H Friis, Department of Epidemiology, Institute of Public Health, University of Copenhagen, Panum Institute, Blegdamsvej 3, DK-2200 Copenhagen, Denmark. E-mail: h.friis{at}pubhealth.ku.dk.
| ABSTRACT |
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Objective: We assessed the effect of prenatal multimicronutrient supplementation on gestational length and birth size.
Design: We conducted a randomized, placebo-controlled, double-blind effectiveness trial among antenatal care attendees in Harare, Zimbabwe. Pregnant women (2235 wk of gestation) were randomly allocated to receive a multimicronutrient or placebo supplement daily until delivery. Supplementation with iron and folic acid was part of antenatal care.
Results: Of 1669 women, birth data were available from 1106 (66%), of whom 360 (33%) had HIV infection. The mean gestational length was 39.1 wk, and 16.6% of the women had a gestational length < 37 wk. The mean birth weight was 3030 g, and 10.5% of the infants had a birth weight < 2500 g. Multimicronutrient supplementation was associated with tendencies for increased gestational length (0.3 wk; 95% CI: 0.04, 0.6 wk; P = 0.06), birth weight (49 g; 6, 104 g; P = 0.08), and head circumference (0.2 cm; 0.02, 0.4 cm; P = 0.07) but was not associated with low birth weight (birth weight < 2500 g) (relative risk: 0.84; 0.59, 1.18; P = 0.31). The effect of multimicronutrient supplementation on birth weight was not significantly different between HIV-uninfected (26 g; 38, 91 g) and HIV-infected (101 g; 3, 205 g) subjects (interaction, P > 0.10).
Conclusion: Antenatal multimicronutrient supplementation may be one strategy to increase birth size.
Key Words: Pregnancy micronutrient supplementation HIV gestational length birth size low birth weight Zimbabwe
| INTRODUCTION |
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Inadequate energy and macronutrient intakes contribute to low birth weight in some settings (7, 8), and efforts to improve the diets of women of reproductive age are of fundamental importance. Nevertheless, multiple micronutrient deficiencies may also contribute to low birth weight, and multimicronutrient supplementation is a cheap and feasible public health intervention, in particular if delivered as part of antenatal care (9).
The United Nations Childrens Fund (UNICEF) has for many years supported developing countries in providing iron and folic acid supplements to pregnant women (10). However, pregnant women are often deficient in a wider range of vitamins and minerals, which can be provided in the same supplement at a marginal extra cost (11). Therefore, a new supplement containing the recommended dietary allowance (RDA) of 15 different micronutrients, including iron and folic acid, has been proposed (12). Two trials from Nepal and Mexico, however, found no additional benefits of micronutrients in addition to iron and folic acid (13, 14), whereas effects on birth weight were found in 2 studies from Africa: a study among HIV-infected Tanzanian women (15) and a recent study among women from Guinea-Bissau, where the HIV prevalence is relatively low (P Kæstel, unpublished observations, 2004).
We assessed the effects of a prenatal multimicronutrient supplement on gestational length and birth size in a randomized, controlled effectiveness trial in Harare, Zimbabwe, where HIV infection is common but malaria is not endemic. Recruitment was up to 36 wk of gestation, because women in developing countries usually attend antenatal care late in pregnancy and because both micronutrient requirements and fetal growth increase toward the end of pregnancy. The supplement contained 3000 µg vitamin A and the RDA of 11 additional micronutrients, excluding iron and folic acid, which were provided through antenatal care. Data on micronutrient status (16, 17), body composition (18), and HIV viral load (19) was reported previously.
| SUBJECTS AND METHODS |
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Women registering for antenatal care at the Edith Oppermann Maternity Hospital (EOMH) were informed about the study, and those who were between 22 and 36 wk of gestation were offered inclusion. The women were informed about HIV testing and counseled before they gave their written consent to participate. Counseling was provided by a nongovernmental organization, AIDS Counseling Trust. HIV results were made available within 2 wk, when those who wished to know their results received posttest counseling. A questionnaire was administered, and clinical examination and blood sampling were done. A research nurse obtained demographic data and medical and obstetric histories. Gestational age at recruitment and gestational length of pregnancy were calculated from the first day of the last menstruation or estimated by using fundus height. Antiretroviral drugs for prevention of mother-to-child transmission were not available. The initial sample size of 1700 was chosen to have 80% power to detect an 80-g difference in birth weight, with the assumption of a mean (± SD) of 3000 ± 500 g, with a significance level of 5%, and allowance for 20% loss to follow-up.
Permission was obtained from the ethical and scientific committees of the Medical Research Council of Zimbabwe, the Harare City Health Department, and the Ministry of Health. The Danish Central Medical Ethics Committee also approved the study. The national Ministry of Health recommendations were adhered to when giving women information on breastfeeding. Women who were found to be sick during clinical examination were referred for treatment at the EOMH or the Harare Central Hospital.
Examinations of the mothers
Clinical examinations of the mothers were done as part of antenatal care. Heights were measured to the nearest 0.1 cm and weights to the nearest 0.1 kg. Venous blood was collected, and serum was separated and stored in liquid nitrogen at 196 °C until tested for HIV. Samples found to be negative with the Genelavia Mixt HIV-1/2 enzyme immunoassay kit (Sanofi, Paris, France) were reported as negative. Positive and indeterminate samples were further tested by using the Recombigen HIV-1/2 enzyme immunoassay kit (Cambridge Biotech, Dublin) with different antigens from those in the Genelavia kit. Samples that were positive or indeterminate with the Recombigen kit were tested at the Department of Clinical Chemistry, Aalborg University Hospital, Aalborg, Denmark, by using an in-house reverse transcriptase-polymerase chain reaction method (20).
Study intervention
The study intervention was a daily tablet containing approximately the RDA for pregnant or lactating women of 13 micronutrients (21), except for vitamin A, for which a higher amount was given. The composition of the multimicronutrient supplement is shown in Table 1
. An iron and folic acid supplement was given separately as part of routine antenatal care and was therefore not included in the multimicronutrient tablet. Similarly, iodine was not included because salt is iodized in Zimbabwe.
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The study participants were numbered consecutively at recruitment. After baseline examinations, each participant was given a container with the same number and instructed to take one tablet with a meal every morning until delivery. For the women who delivered their infants at the EOMH, the remaining tablets were counted, and the number of tablets taken was estimated and used as a measure of compliance.
Birth records
Infants delivered at the EOMH were weighed, and length and head circumference were measured within 72 h by a trained research nurse. Birth weight was determined to the nearest 0.01 kg by using a Sohnle infant scale (Sohnle, Murrhardt, Germany). Length and head circumference were measured with a portable measuring mat and a measuring tape, respectively, to the nearest 1 cm. When study participants were not seen by the research nurse at the EOMH after delivery, the place of delivery was established through home visits. Birth records were later retrieved, and the necessary routine data were extracted. As standard procedure, all health centers keep antenatal records. The delivery records contain demographic information (name, address, and date of birth), obstetric history, plurality (ie, twins or triplets), vaginal or cesarean delivery, episiotomy, etc. In addition, birth weight, head circumference, and length of the infant were recorded. All data were recorded within 72 h.
Statistical analysis
All singletons and the firstborn of multiple pregnancies were included in the analysis, which was based on intention to treat. The outcome variables were measurements of gestational length and birth size (ie, birth weight, length, and head circumference). Based on these measurements, the ponderal index [birth weight [in kg)/length3 (in m)], percentage of infants delivered preterm (gestational length < 37 wk), percentage of infants with a birth weight < 2500 g, and percentage of infants with intrauterine growth retardation-low birth weight (IUGR-LBW, defined as gestational age > 37 wk and birth weight < 2500 g) were computed.
Data were analyzed by using SPSS version 11 (SPSS Inc, Chicago). The distribution of the continuous outcome variables conformed to normality as assessed by normal probability plots. The two-sample t test and the chi-square test were used to test for differences in means and proportions, respectively. The effects of the intervention were presented as differences in means for continuous variables and as relative risks for binary variables. All effect measures were given with 95% CIs. Effect estimates were presented after stratification by maternal HIV infection status, despite the lack of statistical interaction between the intervention and HIV infection status.
Multiple linear and logistic regression analysis was used to assess for effect modification and confounding by maternal HIV infection status, gravidity, season of delivery, anemia, and infant sex. If the P for interaction was <0.10, then interaction terms were computed to allow estimation separately for each level of the effect-modifying variable.
| RESULTS |
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0.15) (Table 5
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The mean number of days from recruitment until delivery was 69 (95% CI: 67, 71). Among the 558 (52.8%) women for whom tablet intake could be assessed, the mean number of tablets taken was 62 (95% CI: 59, 64), and the mean compliance, expressed as the percentage of days from recruitment to delivery when a tablet was taken, was 80%. The mean tablet intake did not differ significantly between the multimicronutrient and placebo groups (62 compared with 62, respectively; P = 0.96).
| DISCUSSION |
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Interestingly, the almost 50-g mean increase in birth weight that was seen in the present study was not confined to the infants in the lower range of the birth weight distribution. An effect of micronutrient supplementation on birth weight may be mediated by prevention of growth-inhibiting maternal or fetal micronutrient deficiencies or by reduction of the effect of infectious disease morbidity on fetal growth. A larger effect of micronutrient supplementation in HIV-infected women was therefore expected because even early asymptomatic HIV infection seems to increase micronutrient requirements (26, 27). However, the point estimates were not significantly different between the HIV-infected and the HIV-uninfected women in the present study.
The loss to follow-up was high because many women went to rural areas to deliver, and this was temporarily exacerbated by civil unrest. In addition to reducing the statistical power of a study, loss to follow-up may introduce bias if it is associated with both the intervention and the outcome. However, in the present study, there was little difference in baseline variables between those who were followed-up and those who were lost to follow-up. More importantly, the loss to follow-up was similar in the micronutrient and placebo groups. The study was an effectiveness trial because the participants were given all tablets at recruitment and were advised to take one tablet daily up to delivery. Because the women were not seen again before delivery, if at all, there were no opportunities to supervise or encourage adherence to the tablet-taking regimen. Consequently, adherence was not optimal, with only one-half of the women taking >85% of the tablets. Because data on compliance were obtained from only one-half of the women, the data do not permit assessment of a dose-response relation. It is likely that compliance was lower among those from whom data were not available. The effects reported here may reflect what can be expected during programmatic implementation. Similarly, the routine iron and folate intakes were not assessed.
Although our study predates the initiative by UNICEF to replace the current iron and folic acid prenatal supplement with a new supplement containing 13 additional micronutrients, the composition and doses are similar, albeit not identical (12). As for differences in composition, iron and folic acid were not included in the supplement tested but were given separately as part of routine antenatal care. Similarly, iodine was not included because salt is iodized in Zimbabwe. Our supplement contained the 12 remaining micronutrients contained in the UNICEF supplement. The main difference in doses between our supplement and the UNICEF supplement was that our supplement contained 3000 µg retinol equivalents preformed vitamin A and 3.5 mg ß-carotene; the doses of the remaining 11 micronutrients in our supplement were similar to those in the UNICEF supplement (ie, approximately the RDA).
Few such studies on the effect of multimicronutrients have been conducted (28). However, several studies to assess the effect of the new UNICEF prenatal supplement and supplements with different compositions or higher doses are currently in progress. Some of these studies not only have birth size as an outcome, but are also powered to study effects on perinatal and neonatal mortality. These studies were recently described in detail (29). A trial among Mexican women compared the effect of a supplement with 13 micronutrients (11.5 times the RDA) and iron with the effect of iron alone (14). Despite the facts that the women were recruited before week 13 of gestation and that the supplements were consumed under supervision, no effects were detected. In Nepal, 4 different micronutrient supplements were compared with placebo (13). Iron and folic acid increased birth weight by 37 g (95% CI: 16, 90 g), whereas neither folic acid alone nor iron, folic acid, and zinc combined had any significant effect. The effect of the multimicronutrient, which included iron, folic acid, and zinc, was of the same magnitude as that of iron and folic acid. Thus, adding more micronutrients to the iron and folic acid supplement produced no additional benefit in terms of improving birth weights. In contrast, a recent trial in Guinea-Bissau found that the UNICEF tablet increased birth weight but that a similar tablet containing 2 times the RDA had a larger effect (P Kæstel, unpublished observations, 2004).
Among HIV-infected pregnant women in South Africa, vitamin A supplementation was shown to reduce the risk of preterm deliveries (30). This result was not found in a similar study in Malawi, in which vitamin A increased birth weight by 95 g (31). In contrast to these studies, a study among pregnant Tanzanian women with HIV did not find an effect of vitamin A on either preterm delivery or birth weight (15). Nevertheless, multivitamin supplementation, which was assessed simultaneously by using a two-by-two factorial design, halved the risks of fetal loss, preterm delivery, and low birth weight and increased mean birth weight by 150 g. The dose of vitamin A in the Malawi trial was similar to ours, whereas the vitamin A intervention in both the South African and the Tanzanian trials consisted of 1500 µg retinol equivalents preformed vitamin A and 30 mg ß-carotene. The multivitamin intervention in the Tanzanian trial contained large doses of B vitamins, vitamin C, and vitamin E. In contrast to the Tanzanian trial, the present study did not assess the effects of the intervention on mother-to-child HIV transmission. However, we were able to assess interactions between multimicronutrient supplementation and HIV infection for various birth size outcomes. Although the effect on birth weight appeared to be larger among the HIV-infected women, this could not be substantiated by statistical tests of interaction.
In a randomized, placebo-controlled, double-blind effectiveness trial, we found that daily multimicronutrient supplementation of pregnant Zimbabwean women was associated with marginally significant effects on several birth-size variables. Given differences in micronutrient status, the coexistence of multiple deficiencies, and micronutrient-micronutrient interactions, the effects of similar interventions might differ across populations. Although multimicronutrient supplementation may be beneficial in increasing birth weight and in HIV-afflicted populations, its effects on a broader range of maternal and infant health outcomes need to be assessed, and effect modifiers need to be identified.
| ACKNOWLEDGMENTS |
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The study was conceived and planned by HF, EG, NN, and KFM. Field and laboratory work was done by HF, EG, NN, PN, and HK. Data processing was done by HF and PK. The first draft of the manuscript was written by HF, and all authors contributed to the final version. None of the authors had any conflicts of interest.
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