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Department of Social Medicine, Federal University of Pelotas, Pelotas, RS, Brazil
2To whom correspondence should be addressed. E-mail: inasantos{at}uol.com.br.
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ABSTRACT |
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 TOP ABSTRACT SUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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68% of the mothers. Crude analyses showed a 30% increase in the risk of SGA among daily maté drinkers compared with nonconsumers (prevalence ratio = 1.3; 95% CI 1.1–1.6), whereas no statistical association was detected with preterm births. After controlling for confounders, the significance of the association with SGA birth no longer held and the lack of association with prematurity remained unchanged. In conclusion, prevalence of daily maté drinking was high among pregnant women and, contrary to the hypothesis, no harmful effect on intrauterine growth or duration of pregnancy was detected.
KEY WORDS: • small for gestational age • preterm • maté • Ilex paraguayensis
In Southeast Latin America, including Argentina, Uruguay, southern Brazil, and Paraguay, the hot infusion of Ilex paraguayensis (maté) is a very popular type of beverage (1). It was used by the native indigenous people long before the arrival of the first Spanish colonists in the 16th century.
Studies on the role of maté in human health have focused predominantly on cancer research. Several studies reported an association between maté drinking and cancer of the upper digestive tract with a focus on the thermal injury theory of carcinogenesis (2,3), without discarding the potential responsibility of the diverse components of maté in such an association.
Among numerous chemical compounds present in maté, caffeine, theobromine, and a number of chlorogenic acids were identified. The role of caffeine in human health has been examined extensively. Caffeine intake, especially during pregnancy, was studied in relation to several adverse reproductive events, based on the fact that caffeine ingested by the mother is rapidly absorbed from the gastrointestinal tract into the bloodstream, readily crosses the placenta, and is distributed to all fetal tissues. Potential effects of caffeine on fetal development may occur after prolonged accumulation of caffeine in pregnant women and passage to the fetus, which lacks the enzymes necessary to metabolize it (4,5).
In South American countries, a relevant source of caffeine, and sometimes the most important one, is maté drinking. A population-based study on the epidemiology of maté drinking conducted previously in Pelotas (a city in Southern Brazil) showed that 30% of the women aged 20–40 y were daily drinkers, and among them, the mean daily intake was 1800 mL maté (6). In a case-control study conducted in 1992, in the same city (7), in which maté drinking was defined as the consumption of any amount of maté at least once a week in any trimester of pregnancy, intake was reported by 72.1% of the mothers in the control group.
Because caffeine was the best-studied component and was also indicated as a risk for adverse pregnancy outcomes (8–10), it would be expected that maté drinking would also be associated with adverse pregnancy outcomes. The objective of the present study was to test the hypothesis that maternal maté drinking during pregnancy was associated with poor neonatal outcomes (preterm and small for gestational age birth).
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SUBJECTS AND METHODS |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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330,000 inhabitants; >99% of all deliveries take place in hospitals. During 1993, a population-based study was conducted in Pelotas, and the 5 maternity hospitals of the city were visited daily. A detailed description of the methodology of the study is given elsewhere (11,12). Two pediatricians and 7 senior medical students interviewed all mothers soon after delivery with a pretested structured questionnaire focused on demographic, environmental, and socioeconomic variables, as well as on characteristics of pregnancy, labor, delivery, and health care utilization. Children were weighed naked using 10-g precision scales and their supine length measured using specially designed length boards (AHRTAG baby length measures). The newborn birthweight was recorded by the maternity hospital staff. Gestational age was assessed for all babies according to the Dubowitz score (13) in the first 24 h after birth. The scales were checked weekly with standard weights. Standardized procedures were used in all measurements. The questionnaire also collected information on the following variables, some of which are potential confounders: maternal anthropometric measures, marital status, family income, crowding, level of education of the mother and her partner, mother’s age, smoking during pregnancy, prenatal care attendance, obstetric history, and morbidity during pregnancy.
For the purpose of the present analysis, babies from multiple pregnancies were excluded. The analysis included 5189 births, comprising 5168 live births and 21 late fetal deaths. Post hoc analysis indicated that, given the observed prevalence of preterm and small for gestational age (SGA)3 births among the unexposed mothers and the ratio unexposed:exposed of 1:1 (considering daily drinkers as the exposed category), the studied sample had a power of 80% to detect relative risks 
1.3, setting 
= 0.05.
Outcomes investigated were preterm birth (birth occurred before 37 complete weeks of pregnancy) and SGA [birthweight <10th percentile for gestational age and gender according to the reference curve developed by Williams et al. (14)].
Women who were single, widowed, divorced, or living without a partner were classified as single mothers. Family income in the month before delivery was expressed as minimum wages (MW)/mo (US$50 in 1993). Parents’ formal education was categorized as: 0, 1–4, 5–8, and 9 complete school years. Maternal age was defined as complete years at time of delivery and categorized as: <20, 20–24, 25–29, 30–34, and 35 y. Maternal skin color was categorized as white and nonwhite according to the interviewer’s observation.
Maternal height was measured by the research team at the hospital and expressed in centimeters. Prepregnancy weight was obtained from prenatal records at the woman’s first antenatal visit or, in their absence, by maternal recall at the time of delivery in kilograms. These data were used to calculate the prepregnancy BMI, weight (kg)/height (m)2. Prepregnancy BMI was categorized into the following groups: <18.5, 18.5–20.9, 21.0–24.9, 25.0–29.9, and 30 kg/m2.
Reproductive history included number of abortions, stillbirths, and preterm and low birthweight births. Parity indicated the number of previous births and was categorized as 0, 1, 2, and 3. Smoking status during the 3rd trimester of gestation and frequency of consumption of alcohol and maté throughout the entire pregnancy period were based on maternal report. Mothers were defined as smokers if they smoked at least 1 cigarette/d. The number of cigarettes smoked was categorized as 0, 1–5, 6–10 and >10 cigarettes/d. Women were defined as alcohol consumers if they drank any amount of alcohol at least once a week during pregnancy. Mothers were defined as maté consumers if they reported drinking any amount of maté at least once a week regularly during the entire pregnancy period. Weekly frequency of maté drinking (number of days per week the woman used to drink maté) was categorized as 0, 1–6 and 7 d/wk.
The quality of antenatal care was assessed using the Kessner Index modified by Takeda (15) and categorized as adequate (6 antenatal care appointments and starting antenatal care wk 20 of pregnancy), inadequate (starting antenatal care after wk 28 of pregnancy or <3 appointments) and intermediate (the remaining situations).
Information regarding morbidity during pregnancy (arterial hypertension, diabetes, and urinary tract infection) was collected through maternal report and was confirmed by a review of antenatal and/or delivery hospital records. Women with chronic hypertension and/or preeclampsia/eclampsia were classified as presenting arterial hypertension. Women with a history of diabetes and those who developed gestational diabetes mellitus were classified as having diabetes.
Crude association between outcomes (preterm and SGA birth) and independent variables was explored using the 
2 test. Statistical significance was defined as a 2-tailed P-value < 0.05. Only potential confounders of the association between maté intake and the outcomes (preterm and SGA birth) were entered in the multivariable analysis. Potential confounders were the variables associated with both the outcomes considered and maté drinking, and not an intermediate step in the causal link between maté intake and preterm and SGA birth (16). Multivariate analyses were carried out through Poisson regression with robust variance. This type of analysis was adopted because it provides direct estimates of relative risks and is a better alternative, comparatively, than logistic regression, for the analysis of cross-sectional studies with binary and high prevalent outcomes (17). For the analysis of the effect of maté drinking on preterm birth, the following variables were found not to act as confounders and were left out of the adjusted analysis: marital status, maternal age, prepregnancy BMI, previous preterm birth, alcohol drinking during pregnancy, attendance at prenatal care, and morbidity during pregnancy (hypertension, diabetes, and urinary tract infection). For the same reason, in the analysis of the effect of maté drinking on SGA birth, prepregnancy BMI, previous preterm birth, alcohol drinking during pregnancy, attendance at prenatal care and morbidity during pregnancy were left out of the adjusted analysis.
All analyses were performed using STATA® version 8.0 software. The study protocol was approved by the Ethical Committee of the Faculty of Medicine, Federal University of Pelotas.
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RESULTS |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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9 complete years of education. A similar distribution was observed with respect to the father’s education.
Maternal demographic characteristics were as follows: 77.3% had white skin color, 17.6% were adolescents (<20 y old), and 11% were 35 y old. The prevalence of prepregnancy BMI < 18.5 kg/m2 was 8.8%, whereas 4.8% of mothers were obese before becoming pregnant (prepregnancy BMI 30.0 kg/m2). Concerning reproductive history, 35% were in their first pregnancy; for the others, the reported prevalence of low birthweight, preterm birth, abortion, and fetal death in previous pregnancies was 14.7, 10.8, 27.9, and 2.6%, respectively.
Maternal habits were as follows: nearly 30% of the mothers were daily smokers during the 3rd trimester of gestation and 5% consumed alcoholic beverages at least once a week throughout pregnancy; 68% of the women reported being maté drinkers (maté consumption at least once a week regularly during the entire pregnancy) and 70% of them were daily consumers (the equivalent to a prevalence of 47.5% of daily drinkers in the entire sample). Maté drinkers were more frequently smokers and consumers of alcoholic beverages than their counterparts (36.8 vs. 15.6%, P < 0.001; and 6.0 vs. 3.0%, P < 0.001, respectively). Maté drinking was also associated with lower family income (19.5% earning 
1 MW vs. 16.6%, P < 0.001) and fewer years of education (2.8% illiterate vs. 1.9%, P < 0.001). The majority of the mothers attended adequate antenatal care (82.8%). The prevalence of arterial hypertension, diabetes, and urinary tract infection was 15.7, 2.8, and 33.5%, respectively.
In crude analysis, mothers whose partners had fewer years of education, and maternal characteristics as prepregnancy BMI < 18.5 kg/m2, inadequate antenatal care and history of abortion, low birthweight or preterm birth were associated with a higher prevalence of preterm delivery. Prevalence of prematurity was also higher among women with a medical history of arterial hypertension and urinary tract infection.
Single mothers and mothers with low family income, fewer years of education, nonwhite skin color, <20 or 35 y old, nulliparae or multiparae, smokers, underweight, and those who had inadequate antenatal care had a higher prevalence of SGA birth. Arterial hypertension and previous history of low birthweight birth were also associated with higher frequency of SGA birth. Diabetes was a protective factor for SGA delivery [prevalence ratio (PR) = 0.4; 95% CI 0.2–0.9; P = 0.04].
In crude analysis, maté drinking was not associated with preterm birth, but was significantly associated with SGA birth, with higher frequencies of SGA for maté drinkers as compared to nondrinkers (P = 0.007). Women who drank maté daily had a 30% increase in the risk of delivering a SGA baby compared with nonconsumers (PR = 1.3; 95% CI = 1.1–1.6; P = 0.03).
The lack of statistical significance of maté drinking on preterm birth in the crude analysis remained unchanged after adjusting for potential confounding factors (Table 1). Parity, previous abortion, and previous low birthweight were the only variables that continued to be significant in the model. When variables related to maternal reproductive history (previous abortion, preterm, fetal death, and also previous low birthweight) were excluded from the model, maté drinking continued not to be associated with preterm birth (P = 0.8). None of the other variables were significant in the model.
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DISCUSSION |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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In addition to maté, other sources of caffeine, a potential putative component of maté, were not investigated in the current study. Data from the case-control study previously conducted in Pelotas (7) showed that coffee was the source of caffeine most frequently consumed; it was reported by 92.7% of all mothers. Among mothers who reported maté consumption, however, maté was the main source of caffeine in the diet, accounting for a mean consumption of 94.5 mg/d. Moreover, among non-maté drinkers, caffeine intake from other sources was significantly lower than among consumers (mean daily caffeine consumption from all other sources was 128.7 ± 149.1 and 227.5 ± 210.6 mg/d, respectively; P < 0.001).
Only weekly frequency and not the amount of maté consumed was investigated. In terms of caffeine, local measures previously undertaken showed that 100 mL of maté contains 17 mg of caffeine. Daily consumers drink in average 1800 mL of maté/d (7), which is equivalent to 300 mg of caffeine, the cutoff point for heavy caffeine intake during human pregnancy. In this way, daily consumption of maté is a reliable surrogate of the consumption of a high amount of caffeine.
Changes in the pattern of maté consumption in different periods of pregnancy could also lead to nondifferential misclassification errors of exposure estimation. Although women can reduce the intake of beverages such as coffee during pregnancy (20), evidence exists from other studies that the mean consumption of beverages such as coffee and maté remain constant throughout the gestational period (7,18,21).
Another issue that must be considered is that in South Brazil, maté is typically consumed by sharing the straw, which may constitute a potential source of periodontal and other infections. In some studies, periodontal disease has been associated with poor pregnancy outcomes (22,23). If lack of information on periodontal disease was a source of bias in this study, it would have distorted the results away from the unit, spuriously increasing the effect of the exposure. It seems not to be the case in the current study because no association between maté and birth outcomes was found.
Maté drinking is the main source of caffeine in the studied population; this fact distinguishes our pattern of caffeine consumption from that of other countries in which coffee and tea are the major sources of caffeine in the adult diet (24). To the knowledge of the authors, no other studies have investigated the influence of maté drinking on preterm or SGA birth.
Maté drinking had no association with preterm birth, neither in the crude nor in the adjusted analysis. For SGA birth, the crude association observed between maté drinking and SGA was in fact the result of confounding by maternal education.
The consistency of the results obtained from 2 independent population-based investigations conducted in Pelotas in subsequent years (1992 and 1993) suggests that the amount of maté regularly consumed during pregnancy in South Brazil is probably safe for the fetus.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Abbreviations used: MW, minimum wage; PR, prevalence ratio; SGA, small for gestational age.
Manuscript received 22 December 2004. Initial review completed 7 February 2005. Revision accepted 1 March 2005.
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LITERATURE CITED |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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