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Too heavy, too late: investigating perinatal health outcomes in immigrants residing in Spain. A cross-sectional study (2009–2011)
  1. Sol P Juárez1,2,
  2. Bárbara A Revuelta-Eugercios1,3
  1. 1Centre for Economic Demography, Lund University, Lund, Sweden
  2. 2Institute for Futures Studies, Stockholm, Sweden
  3. 3Institut National d'Études Démographiques, Paris, France
  1. Correspondence to Dr S Juárez, Centre for Economic Demography, Lund University, Box 7083, Lund SE-22007, Sweden; sol.juarez{at}ekh.lu.se

Abstract

Background Studies have shown that immigrants residing in Spain have lower risks of delivering low birthweight (LBW) and preterm babies despite their socioeconomic disadvantages (the healthy migrant paradox). However, less is known about other important perinatal outcomes derived from birth weight and gestational age such as macrosomia and post-term birth. This paper aims to compare the main indicators related to birth weight and gestational age (LBW, macrosomia, preterm and post-term) for immigrants and Spaniards.

Methods Cross-sectional study based on the Spanish vital statistics for years 2009–2011. Multinomial regression models were performed to obtain crude and adjusted ORs and their 95% CIs.

Results After adjusting for known confounders, compared with Spaniards, most immigrant groups show lower or not significantly different risks of delivering LBW (OR between 0.65 and 0.87) or, more exceptionally, preterm babies (between 0.75 and 0.93). However, most of them also show higher risks of delivering macrosomic (OR between 1.21 and 2.58) and post-term babies (OR between 1.11 and 1.50). Mothers from sub-Saharan Africa show a higher risk in all perinatal outcomes studied.

Conclusions The immigrant health paradox should be carefully assessed in comprehensive terms. Together with a predominantly lower risk of LBW, most immigrants have a higher risk of macrosomia, post-term and preterm births. These results have policy-making implications since studying the right tail of the birth weight and gestational age distributions implies considering a different set of risk factors.

  • MIGRATION
  • PERINATAL EPIDEMIOLOGY
  • PERINATAL

https://doi.org/10.1136/jech-2013-202917

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    Introduction

    Birth weight and gestational age are essential variables to assess perinatal health outcomes, as they are strongly associated with newborn survival and health status across the life course.1–5 Additionally, they also inform about maternal health, since they depend on maternal nutritional status and lifestyle.6 ,7

    Previous studies have shown that immigrant mothers residing in some developed countries have better health outcomes compared with natives.8–13 This finding is known in the literature as the ‘immigrant health paradox’ or ‘epidemiological paradox’,13 ,14 as migrants are expected to come from poorer backgrounds and experience socioeconomic disadvantages in the host country, thus faring worse than natives. Evidence of this phenomenon on perinatal outcomes has been mostly reported in the USA for Hispanics,8 ,9 ,15 but also in other European contexts,12 ,13 ,16 ,17 suggesting its universality.13 A recent literature review shows that the advantage varies by migrant subgroups,18 while other studies underline that it is outcome-specific and varies with time of residence.19 However, within this literature, insufficient attention has been paid to other perinatal outcomes derived from gestational age and birth weight, such as post-term delivery and macrosomia, also very relevant from a general health perspective. Post-term babies have higher risk of perinatal mortality20 and of suffering from attention deficit and hyperactivity disorders in early childhood.21 Similarly, macrosomic babies present low Apgar scores more frequently and higher risk of being treated at intensive care units,22 postneonatal death,22 ,23 obesity in adulthood24 ,25 and psychiatric disorders later in life.26

    The aim of this paper is to investigate differences between natives and migrants in the main indicators derived from birth weight and gestational age. We will explore the commonly used indicators of low birth weight (LBW) and preterm birth but also macrosomia and post-term deliveries. We use information from Spain for the period 2009–2011 (the last years available), where the epidemiological paradox has already been found for preterm birth and LBW in previous years.13 ,27 ,28 Migrants in Spain account for 12% of the population (50% women), all arriving in the last 10 years.

    Methods

    Study design, setting and participants

    We performed a retrospective cross-sectional study based on the 2009–2011 Spanish Vital Statistics, comprising all babies born in Spain (N=1 453 571). The data is publicly available from the National Institute of Statistics (NIS). We selected live births and single deliveries (final N=1 393 095).

    Variables

    We study indicators at birth derived from birth weight and gestational age: LBW (<2500 g), macrosomia (>4500 g), preterm birth (<37 completed gestational weeks) and post-term birth (≥42 completed weeks). Missing data in gestational age (18.11%) or birth weight (4.99%) were excluded from the analyses for the corresponding variable.

    We classified mother's country of birth into 11 groups attending to geographical and cultural similarities: Spain; European Union-15 (Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands, Portugal, Spain, Sweden and UK); European Union-Extension (the last 12 countries added to the EU-15: Bulgaria, Cyprus, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Romania, Slovakia and Slovenia); Non EU-Europe (Ukraine, Moldavia, Byelorussia, Georgia, Bosnia, Croatia, Armenia, Russia, the ex-Yugoslavian republics and Macedonia); North of Africa; sub-Saharan Africa; USA & Canada; Central America & Mexico; the Caribbean; South America; and Asia. Mothers with no information on place of birth (N=7315) were included as an additional missing category.

    Statistical analyses

    We applied multinomial regressions to model categories of birth weight (LBW, normal birth weight and macrosomia), gestational age (preterm, at term and post-term) and LBW and macrosomia for term babies. Crude models included only mother's place of birth, but adjusted models included factors that could be unevenly distributed across immigrants and therefore confound the results: mother's age, occupation and marital status, father's place of birth and occupation, newborn's sex, birth order, Spanish community of residence and year of birth. ORs and their corresponding 95% CIs are presented.

    Results

    Table 1 shows mothers’ socioeconomic and demographic characteristics. The largest proportion of mothers younger than 24 years comes from EU-Extension (28.0%), North Africa (27.9%) and the Caribbean (28.5%), while the largest proportion of mothers 35 years or older is found among natives and mothers from EU-15 (39.4%), and USA & Canada (36.4%). Of mothers born in North Africa 68.7% have primary studies only, followed by sub-Saharan Africa (57.3%) and Asia (46.3%). The greatest proportion of unmarried mothers is observed among the groups from the Caribbean (61.1%) and South America (55.1%). Mothers from EU-Extension and Asia show the largest proportion of women employed in blue-collar occupations (42.0% and 48.1%, respectively). Those originally from North Africa (83.3%), EU-Extension (78.0%) and Asia (79.7%) show the largest proportion of blue-collar workers among fathers. The largest proportion of non-native fathers is found in the group of mothers from Asia (91.9%) and North Africa (88.9%).

    View this table:
    Table 1

    Characteristics of the births according to maternal place of birth

    Figure 1 shows the prevalence of the perinatal outcomes by maternal country of birth. Immigrants appear to be a vulnerable population when looking at the prevalence of preterm birth (except EU-15, Non EU-Europe and USA & Canada), post-term birth and macrosomia. In contrast, they show a lower prevalence of LBW babies than Spaniards (with the exception of mothers from EU-Extension, sub-Saharan Africa, and the Caribbean).

    Figure 1
    Figure 1

    Prevalence of low birth weight (LBW), macrosomia, preterm birth and post-term birth by maternal origin.

    Table 2 shows the results of multinomial regressions for gestational age. Regarding preterm births, lower risks than natives are found for USA & Canada in the crude model (OR: 0.73) and, after adjustment, for mothers from EU-15 and rest of Europe (OR: 0.93 and 0.91, respectively). Contrarily, higher risks than natives are found for other groups in both models (adjusted OR: non-EU 1.22; sub-Saharan Africa 1.17; the Caribbean 1.12; South America 1.03; and Asia 1.23). No statistically significant differences are found between mothers from Central America & Mexico and Spain. Regarding post-term babies, most groups show higher risks than Spaniards. The highest risks are found for North Africa, Non-EU Europe and Sub-Saharan Africa (OR: 1.50, 1.34 and 1.26, respectively). No statistically significant differences are found for mothers from USA & Canada, Central America & Mexico, South America and Asia.

    View this table:
    Table 2

    Multinomial regression models for gestational age

    Table 3 shows that the risk of LBW is significantly lower for most immigrant groups before and after adjustment. Higher risks are found only for sub-Saharan Africa in both models (OR: 1.26 and 1.18, respectively) and no differences for EU-15 and USA & Canada. In contrast, a higher risk of delivering macrosomic babies appears in mothers from all groups in the crude and adjusted models but Asia, which shows no differences. The highest risk is for Central America & Mexico (adjusted OR: 2.58). When restricting the sample to babies born at term, the direction of LBW and macrosomia risks remains the same.

    View this table:
    Table 3

    Multinomial regression models for birth weight

    Discussion

    Our results support challenging the universality of the epidemiological paradox. When looking at the indicators traditionally studied, LBW and preterm birth, we mainly find migrant advantages. All groups show a lower risk of LBW with the exceptions of EU-15 and USA & Canada, with no conclusive differences, and sub-Saharan Africa, who show a significantly higher risk. These results support previous evidence in Spain for most groups29 ,30 and a disadvantage for babies of sub-Saharan descent.30 ,31 The advantage is also observed among LBW at term babies (proxy of babies with intrauterine growth restriction).

    For gestational age, however, we find a higher risk of preterm birth for groups who had shown advantages in earlier studies (period before 2006),30 ,31 such as South America, the Caribbean and EU-Extension. The pattern we observe seems consistent over very (<32 gestational weeks) and moderate preterm (>32 gestational weeks and <37 gestational weeks) (data not shown in tables). Conversely to the above mentioned outcomes, the results on macrosomia and post-term birth indicate an overall disadvantage. Post-term risk was significantly higher for EU-15, EU-Extension, Non-EU Europe, North Africa and the Caribbean. Macrosomia risk is higher for all migrants (with the exception of Asia). This finding seems to have been at work for some time as a sensitivity analysis shows similar results for 2005–2006.

    Research on preterm birth and LBW has pointed out that selection in origin and cultural values that discourage women from engaging in negative health behaviours may compensate for, and even counterbalance, the risks associated with belonging to a socioeconomically disadvantaged group.30 ,32 However, the absence of this advantage on the other side of the distribution may suggest the possibility that immigrants and Spaniards are affected by different sets of risk factors, creating different populations at risk at birth (LBW vs macrosomic and preterm vs post-term). In birth weight, it is possible that tobacco consumption, childbearing at later ages, inadequate weight gain during pregnancy (due to eating disorders, for example), or use of assisted reproductive techniques might affect the host population more strongly, leading to perinatal outcomes in one direction (higher LBW).27 ,33 Other risk factors, such as maternal diabetes and obesity during pregnancy34 may explain the higher risk of macrosomia among immigrants.35 In fact, a high-glycemic diet and a higher consumption of carbohydrates (perhaps linked to their lower cost)24 have been linked to obesity and diabetes during pregnancy.25

    In gestational age, the existence of different sets of risk factors for immigrants and natives is less clear, partially because the determinants of post-term birth are less understood. Late pregnancy diagnosis and/or lack of antenatal care, which might also be caused by lower healthcare utilisation, could lead to differential post-term risks. Previous evidence has indicated that the population of immigrants in Spain, on average, consume less alcohol and smoke less than Spaniards36 and that they have a higher prevalence of obesity,37 lending some support to this hypothesis.

    The differential risk factors for immigrant groups hypothesis is not the only possible explanation. It is also important to note that the results could be the product of the reported nature of the vital statistics and/or the computation of gestational age. First, immigrants are more likely to misreport birth weight and gestational age than natives although, in aggregate terms, the NIS data is quite reliable when compared with hospital records.38 Thus, risk in both tails of the distribution, for instance, may be an artefact due to data quality rather than to worse reproductive health. Second, computation of gestational age may have differed across groups: lower healthcare use may render migrants more likely to recall gestational age based on last menstruation period, which tends to overestimate preterm and post-term birth rates; while Spaniards would be likely to recall ultrasounds.39 In fact, the existence of a bimodal distribution of the weight of preterm infants, observed in previous studies using Spanish vital statistical data,38 supports the existence of gestational age misclassification.40

    The disappearance of preterm advantages for some migrant groups compared with previous research could be related to changes in reporting patterns (thus, an artefact), the process of gestational age shortening, more pronounced among immigrants,41 or the economic crisis starting in 2008.

    It is important to take into account that since 2011 Spain has become a country of emigration (data from NIS). This new context, together with the general reduction of social benefits, and the disappearance of a universal healthcare system, might affect the immigrant population composition and its health conditions. Moreover, those who remain in Spain, although presumably better placed in the labour market, are exposed to worse and worsening-labour conditions affecting well-being and material opportunities. If this is the case, further analyses are needed to understand why this indicator is affected and others are not.

    The joint examination of old and new indicators has uncovered the existence of groups with particularly disadvantaged perinatal outcomes, faring worse in both tails of the distribution. Women from EU-Extension, sub-Saharan Africa and the Caribbean had a higher risk of preterm and post-term births, and those from sub-Saharan Africa had a higher risk of LBW and macrosomia. This situation might suggest heterogeneity within these immigrant populations, which could be related, for example, to the length of time spent in the host country. The case of sub-Saharan Africa is noteworthy as newborns show worse outcomes in all indicators under study, confirming the evidence available.13 ,42

    Using multinomial regression has overcome some of the methodological problems of previous analyses. We have properly identified the reference category (ie, normal weight or term, respectively) by excluding macrosomic and post-term babies, who have been frequently included in the reference group in the past. We are also the first to use maternal country of birth (instead of nationality) for the Spanish setting and to control by maternal education, both included in the Spanish Vital Statistics from 2007. By comparing different outcomes derived from the same measures (birth weight and gestational age) our findings contribute to the debate over the epidemiological paradox lending additional support to studies that challenge its universality.19

    This study also presents some limitations. First, missing data on birth weight and gestational age might be a problem if not normally distributed within mother's country of birth and outcome (ie, if missing data corresponds to babies with adverse perinatal health outcomes). Missing data is more likely to be found among immigrants than Spaniards (after controlling for demographic and socioeconomic variables), especially among mothers coming from Africa and Asia. Missing data on our covariates is also a limitation (which affects correct adjustment). Missing data on maternal country of birth is relatively small and does not seem to correspond to any special group: it shows either no differences or risks similar to the other migrant groups.

    Second, we do not have information about important covariates (eg, whether the mother suffered from diabetes, hypertension or whether she smoked during pregnancy), nor information about the residence length of immigrants in Spain, which has been found to be a modifier as health advantages tend to disappear with time spent in the host country.19 In spite of this important lack of information, the relatively short migration experience of the Spanish context (which mainly dates from the year 2000) warrants more homogeneity to the immigrant population. Third, the differences observed in this study are based on averages, but we acknowledge the importance of studying the variance in order to investigate to what extent country of birth can explain perinatal outcomes.43

    To conclude, this paper supports the outcome and country-specific nature of the epidemiological paradox, even within same variable indicators and uncover the existence of migrant disadvantages on macrosomia (except for Asia) and post-term birth (with some exceptions), which underline the need to better understand why these differences exist. The absence of advantages in preterm birth among certain groups compared with Spaniards stresses the need to understand why these differences have appeared. Some questions, however, remain unanswered: do different sets of risk factors operate for immigrants and Spaniards giving rise to advantages and disadvantages in outcomes derived from the same variable, or is it an artefact of mis-registration and mis-reporting?

    What is already known on this subject?

    • Ample evidence and a recent literature review show that immigrants residing in developed countries have a lower risk of delivering low birthweight and preterm babies (a healthy migrant paradox).

    • Macrosomia and post-term birth are acknowledged indicators relevant for infant health but no attention has been paid to them in relation to the epidemiological paradox.

    What this study adds?

    • This study enquires into the universality of the healthy migrant paradox by showing that while most immigrants in Spain have a lower risk of having low birthweight and preterm babies compared with Spaniards, most of them have a higher risk of delivering macrosomic and post-term babies.

    • Babies born of women from Sub-Saharan Africa have a higher risk in all perinatal outcomes studied, so further attention should be paid to this group.

    • More attention should be devoted to studying macrosomia and post-term birth for migrants. The fact that the perinatal health problems between immigrants and Spaniards are located in different parts of the distributions of birth weight and gestational age suggests that different risk factors may be involved.

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    Footnotes

    • Contributors SJ and BARE had the original idea and contributed to the design of the study; SJ and BARE performed the analyses. SJ wrote the first draft of the manuscript, and the two authors made substantial contributions to the interpretation of the results and manuscript revision. All authors approved the final version of the manuscript.

    • Funding This work was supported by the Swedish Council for Health, Working Life and Welfare (FORTE) (Dnr 2012-1367, PI Kirk Scott) and SIMSAM early life, Lund University (2013-5474). We also acknowledged funding from the Labex iPOPs (Pres heSam), reference ANR-10-LABX-0089, laboratoire INED.

    • Competing interests None.

    • Provenance and peer review Not commissioned; externally peer reviewed.