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Maternal age and adverse perinatal outcomes in a birth cohort (BRISA) from a Northeastern Brazilian city

Idade materna e desfechos perinatais adversos em uma coorte de nascimentos (BRISA) de uma cidade do Nordeste brasileiro

Abstracts

PURPOSE:

To verify the existence of associations between different maternal ages and the perinatal outcomes of preterm birth and intrauterine growth restriction in the city of São Luís, Maranhão, Northeastern Brazil.

METHODS:

A cross-sectional study using a sample of 5,063 hospital births was conducted in São Luís, from January to December 2010. The participants comprise the birth cohort for the study "Etiological factors of preterm birth and consequences of perinatal factors for infant health: birth cohorts from two Brazilian cities" (BRISA). Frequencies and 95% confidence intervals were used to describe the results. Multiple logistic regression models were applied to assess the adjusted odds ratio (OR) of maternal age associated with the following outcomes: preterm birth and intrauterine growth restriction.

RESULTS:

The percentage of early teenage pregnancy (12–15 years old) was 2.2%, and of late (16–19 years old) was 16.4%, while pregnancy at an advanced maternal age (>35 years) was 5.9%. Multivariate analyses showed a statistically significant increase in preterm births among females aged 12–15 years old (OR=1.6; p=0.04) compared with those aged 20–35 years. There was also a higher rate in preterm births among females aged 16–19 years old (OR=1.3; p=0.01). Among those with advanced maternal age (>35 years old), the increase in the prevalence of preterm birth had only borderline statistical significance (OR=1.4; p=0.05). There was no statistically significant association between maternal age and increased prevalence of intrauterine growth restriction.

Maternal age; Gestational age; Premature birth/etiology; Fetal growth retardation; Pregnancy outcome


OBJETIVOS:

Verificar a existência de associaçoes entre diferentes idades maternas e desfechos de nascimentos pré-termo e restrição de crescimento intrauterino no município de São Luís, no Maranhão.

MÉTODOS:

Estudo transversal no qual se utilizou uma amostra composta de 5.063 nascimentos hospitalares em São Luís, região Nordeste do Brasil, de janeiro a dezembro de 2010. As participantes compõem a coorte de nascimentos da pesquisa "Fatores etiológicos do nascimento pré-termo e consequências dos fatores perinatais na saúde da criança: coortes de nascimento em duas cidades brasileiras" (BRISA). Para a descrição dos resultados, utilizaram-se medidas de frequência e intervalo de confiança de 95%. Modelos de regressão logística múltipla foram aplicados para avaliar o odds ratio (OR) ajustado da idade materna associado com os seguintes desfechos: nascimento pré-termo e restrição de crescimento intrauterino.

RESULTADOS:

O percentual de gestantes adolescentes precoces (12 a 15 anos) foi de 2,2%, e daquelas tardias (16 a 19 anos) de 16,4%, enquanto o de grávidas com idade avançada (>35 anos) foi de 5,9%. As análises multivariadas demonstraram um aumento estatisticamente significante na ocorrência de partos pré-termo entre as mulheres na faixa etária dos 12 aos 15 anos (OR=1,6; p=0,04) quando comparadas àquelas de 20 a 35 anos. Também houve aumento entre as mulheres dos 16 aos 19 anos (OR=1,3; p=0,01). Entre aquelas com idade materna avançada (acima de 35 anos), apesar do aumento na prevalência de parto pré-termo, houve significância estatística limítrofe (OR=1,4: p=0,05). Não houve associação estatisticamente significativa entre a faixa etária maternal e o aumento da prevalência de restrição do crescimento intrauterino.

Idade materna; Idade gestacional; Nascimento prematuro/etiologia; Retardo do crescimento fetal; Resultado da gravidez


Introduction

Though female fertility begins around 10 years of age, the period ranging from 18 to 30 years old is when pregnancy has the best chance for success from a biological perspective11. Montenegro CA, Rezende Filho J. Rezende obstetrícia fundamental. 11 ed. Rio de Janeiro: Guanabara Koogan; 2008..

The importance of maternal age on perinatal outcomes has been the subject of numerous studies. Pregnancies that happen at either end of a woman's reproductive life have been associated with adverse perinatal outcomes22. Schempf AH, Branum AM, Lukacs SL, Schoendorf KC. Maternal age and parity-associated risks of preterm birth: differences by race/ethnicity. Paediatr Perinat Epidemiol. 2007;21(1):34–43.55. Mariotoni GG, Barros Filho AA. Peso ao nascer e características maternas ao longo de 25 anos na Maternidade de Campinas. J Pediatr (Rio J). 2000;76(1):55–64..

Pregnancy during adolescence (from 10 to 19 years old)66. World Health Organization (WHO). La salud de los jóvenes: un reto y una esperanza. Ginebra: WHO; 1995. is often associated with poor obstetric and perinatal outcomes. Studies have shown that pregnant adolescents have lower socioeconomic and educational levels, poor prenatal care, and give birth to children with higher rates of low birth weight (LBW) or intrauterine growth restriction (IUGR), and neonatal/childhood mortality77. Bettiol H, Barbieri MA, Gomes UA, Wen LY, Reis PM, Chiaratti TM, et al. Atenção médica à gestação e ao parto de mães adolescentes. Cad Saúde Pública. 1992;8(4):404–13.99. Debras E, Revaux A, Bricou A, Laas E, Tigaizin A, Benbara A, et al. Obstetric and neonatal outcomes of adolescent pregnancies: a cohort study in a hospital in Seine-Saint-Denis France]. Gynecol Obstet Fertil. 2014;42(9):579–84. French.. Several investigations have demonstrated that teenage pregnancy is associated with LBW or IUGR and preterm birth as a result of biological immaturity, which is often worsened by socioeconomic deprivation1010. Del Ciampo LA, Junqueira MJG, Ricco RG, Daneluzzi JC, Ferraz IS, Martinelli Junior CE. Tendência secular da gravidez na adolescência. Pediatria (São Paulo). 2004;26(1):21–6.,1111. 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. J Nutr. 2007;137(2):447–52.. Ribeiro et al.88. Ribeiro ERO, Barbieri MA, Bettiol H, Silva AAM. Comparação entre duas coortes de mães adolescentes em município do Sudeste do Brasil. Rev Saúde Pública. 2000;34(2):136–42., analyzing pregnancy in both early (13–17 years old) and late (18–19 years old) adolescences reinforced this idea when they found adverse social and biological outcomes more frequently in the first group. Younger adolescents were associated with fewer prenatal visits and stable civil unions, and higher rates of LBW and preterm birth. The authors indicated that the negative obstetric outcomes among younger mothers could be related to age and other independent adverse factors.

At the other end of the spectrum, we can mention the pregnancies at advanced maternal age (after 35 years of age). In the past three decades, Brazilian1212. Andrade PC, Linhares JJ, Martinelli S, Antonini M, Lippi UG, Baracat FF. Perinatal results in pregnant women with more than 35 years: a controlled study]. Rev Bras Ginecol Obstet. 2004;26(9):697–701. Portuguese.,1313. Senesi LG, Tristão EG, Andrade RP, Krajden ML, Oliveira Junior FC, Nascimento DJ. Neonatal morbidity and mortality related to pregnant women at the age of 35 and older, according to parity]. Rev Bras Ginecol Obstet. 2004;26(6):477–82. Portuguese.and worldwide1414. Huang L, Sauve R, Birkett N, Fergusson D, van Walraven C. Maternal age and risk of stillbirth: a systematic review. CMAJ. 2008;178(2):165–78.,1515. Jahromi BN, Husseini Z. Pregnancy outcome at maternal age 40 and older. Taiwan J Obstet Gynecol. 2008;47(3):318–21. studies have detected a considerable increase in the number of women who delay motherhood. This phenomenon is driven by the change in women's social roles, the option of investing in training and career developments, and the variety of contraceptive methods available1616. Gravena AA, Sass A, Marcon SS, Pelloso SM. Resultados perinatais em gestações tardias. Rev Esc Enferm USP. 2012;46(1):15–21..

The effects of pregnancy at an advanced maternal age (35 years old or more) in perinatal outcomes have been described by several authors. Two studies conducted in Nigeria showed that primigravidae aged 35 years or older had higher preterm birth rates1717. Ojule JD, Ibe VC, Fiebai PO. Pregnancy outcome in elderly primigravidae. Ann Afr Med. 2011;10(3):204–8. and LBW ones1818. Eleje GU, Igwegbe AO, Okonkwo JE, Udigwe GO, Eke AC. Elderly primigravidae versus young primigravidae: a review of pregnancy outcome in a low resource setting. Niger J Med. 2014;23(3):220–9. than younger women. An investigation carried out in Norway1919. Wang Y, Tanbo T, Abyholm T, Henriksen T. The impact of advanced maternal age and parity on obstetric and perinatal outcomes in singleton gestations. Arch Gynecol Obstet. 2011;284(1):31–7., in 2011, found no significant differences in the rates of preterm birth and LBW between older and younger women. A retrospective study of 1,255 women conducted in Brazil, in 20121616. Gravena AA, Sass A, Marcon SS, Pelloso SM. Resultados perinatais em gestações tardias. Rev Esc Enferm USP. 2012;46(1):15–21., found no differences in the rates of LBW and preterm birth.

Data from studies published in the 1980s that analyzed the influence of maternal age on perinatal outcomes are controversial, which can be partly explained by different methodological approaches, sample sizes, and sample representativeness in addition to significant regional differences. Another factor that may contribute to the controversial nature of these studies is the period during which the studies were developed. In 2000, Mariotoni et al.55. Mariotoni GG, Barros Filho AA. Peso ao nascer e características maternas ao longo de 25 anos na Maternidade de Campinas. J Pediatr (Rio J). 2000;76(1):55–64. studied 18,262 births from 1971 to 1995 in Campinas, São Paulo State, Brazil, divided into five-year periods, and found an association between LBW with pregnancy during adolescence or above 35 years of age. However, this was observed in some of the surveyed periods, but not in all of them. Population-based studies are needed to achieve greater reliability in the observed trends.

The present study used a population-based sampling method and therefore has the potential to fill gaps in our knowledge about the influence of different maternal ages on two adverse perinatal outcomes: IUGR and preterm birth. The objective of this study was to confirm the presence and dimension of these associations in São Luís, which is the capital of Maranhão State, Northeastern Brazil, assuming that these results should resemble the patterns occurring in other capitals in the same region.

In Brazil, particularly in the Northern and Northeastern regions, few studies have addressed the association between maternal age and preterm birth, and even fewer studies have examined the relationship between maternal age and intrauterine growth restriction.

Methods

This study is part of a project entitled "Etiological factors of preterm birth and consequences of perinatal factors on children's health: birth cohorts from two Brazilian cities (BRISA)", which was developed by Universidade Federal do Maranhão (UFMA) in partnership with the Universidade de São Paulo (USP), in Ribeirão Preto campus.

The cross-sectional cohort was composed of 5,063 single live-born infants, who were born in São Luís from January to December 2010. Data were collected in all hospitals in such city, which recorded more than 100 births/year in the previous year, representing 98.7% of the total of hospital births in the city.

The sample was proportionally allocated to the number of births. For the study, a total of 6,000 ones were calculated, representing one third of those of the city in one year. For each hospital participating in the study, a random number from 1 to 3 was drawn to identify the starting point, with a sampling interval of 3. Losses due to refusal or early discharge from the hospital represented 4.6%.

Three survey instruments were used: a birth record, and mother and newborn survey questionnaires.

In the present research, a newborn was considered preterm when the gestational age was less than 37 weeks as calculated from the first day of the last menstrual period. When the only available information was the month, its 15th day was used to calculate the gestational age. An algorithm was applied to identify the gestational age for cases without last menstrual period information, which was determined using a regression model based on birth weight, parity, per capita household income, and newborn's sex. In addition, birth weights above the 99th percentile (British reference curve)2020. Wilcox M, Gardosi J, Mongelli M, Ray C, Johnson I. Birth weight from pregnancies dated by ultrasonography in a multicultural British population. BMJ. 1993;307(6904):588–91. and considered incompatible with gestational age were coded as unknown.

The birth weight ratio described by Kramer et al.2121. Kramer MS, Platt RW, Wen SW, Joseph KS, Allen A, Abrahamowicz M, et al. A new and improved population-based Canadian reference for birth weight for gestational age. Pediatrics. 2001;108(2):E35. was used to establish IUGR. It defines newborns with IUGR presenting a birth weight ratio lower than 0.85. Such ratio is obtained dividing the newborn weight by the weight corresponding to the 50th percentile of the weight curve for the gestational age.

The independent variables analyzed were maternal age, marital status, parity, whether the mother received prenatal care, age-appropriate education, type of delivery, type of hospital (public or private), hypertension during pregnancy, risks for abortion and preterm labor, anemia, and smoking during pregnancy. Maternal age-appropriate education was classified into age-appropriate or not age-appropriate education according to a modified method described by Hellerstedt et al.2222. Hellerstedt WL, Pirie PL, Alexander GR. Adolescent parity and infant mortality, Minnesota, 1980 through 1988. Am J Public Health. 1995;85(8 Pt 1):1139–42., as follows: 19 years or older — 12 years of education was considered age-appropriate; younger than 19 years — the number schooling period was subtracted from age, and results higher than 7 indicated not age-appropriate education.

For the statistical analysis, multiple logistic regression modeling was used to control the influence of each variable alone on the rates of preterm birth or IUGR. The risk between the independent variables and the perinatal outcomes was calculated using odds ratios (OR) with 95% confidence interval (95%CI). All analyses were performed using STATA 11.0 software (Stata Corp., College Station, TX, USA) and the stepwise method to select variables, firstly considering a probability of p<0.20 for inclusion in the model; subsequently, variables with p>0.10 were removed from it. In the final version, p<0.05 was regarded as statistically significant.

This study followed the criteria of Resolution 196/96 of Health National Council, and its complementary resolutions. The interviewees were invited to participate in the study, and they signed informed consent forms, if they agreed to participate. It was approved by the Research Ethics Committee of the University Hospital of UFMA (223/2009).

Results

This study consisted of a sample including 5,063 births after excluding twins, stillbirths and 4 cases of missing birth weight information. Herein, 2.2% of the mothers were women aged 12 to 15 years (early adolescence); 16.4% were 16 to 19 years old (late adolescence); 75.4%, 20 to 35 years; and 5.9%, older than 35 years old. Sociodemographic characteristics, clinical aspects of pregnancy, including frequency of prenatal visits, number of pregnancies and parity, and the most common complications during pregnancy are shown in Table 1.

Table 1
Sociodemographic, clinical, and perinatal characteristics of pregnant women (n=5,063)

In this research, 16.2% of the infants were born with IUGR, while 12.1% were preterm births. Other perinatal characteristics, such as type of delivery, newborn's sex, and place of birth are presented in Table 1.

Only statistically significant results obtained in the multivariate analysis are shown in the tables. There was a significant difference in preterm birth rates between women in the age ranges of 12 to 15 (18.6%; OR=1.6; p=0.04) and 16 to 19 years (14.9%; OR=1.3; p=0.01) with those aged 20 to 35 years, who were considered the baseline category. Among the subjects who are older than 35 years old, despite an increased prevalence of preterm birth compared with the baseline category, only borderline statistical significance was observed (14.3%; OR=1.4; p=0.05).

Among the independent variables analyzed in this study, marital status "without a partner", smoking during pregnancy, lack of prenatal care, primiparity and not age-appropriate education were associated with higher preterm birth rates. In addition, clinical complications of pregnancy, such as hypertension and risk of preterm labor, were associated with higher preterm birth rates.

Multivariate analysis results for preterm birth are shown in Table 2.

Table 2
Adjusted analysis of the association between preterm birth and maternal age, marital status, parity, smoking during pregnancy, prenatal visits, education, hypertension, and risks of preterm labor (n=5,063)

There was no statistically significant association between maternal age and increased IUGR rates. Primiparity, smoking during pregnancy, lack of prenatal care, hypertension in pregnancy, and risk of preterm labor were associated with increased prevalence of IUGR (Table 3).

Table 3
Adjusted analysis of the association between intrauterine growth restriction and maternal age, type of delivery, parity, smoking during pregnancy, prenatal visits, hypertension, and risks of preterm labor (n=5,049)

Discussion

The present study demonstrated that, in this Brazilian population, maternal age of less than 20 years old, and not only early adolescence (younger than 16 years old) but also late one (aged 16 to 19 years) are associated with higher preterm birth rates, while advanced maternal age (>35 years) showed only a borderline association with this outcome. However, maternal age was not associated with IUGR in any of the age groups defined in this study.

In the present study, the percentage of adolescents who gave birth was 18.6%, with 2.2% corresponding to early adolescents and 16.4% to late ones. This value was higher than those observed in developed countries, such as Finland2323. Leppälahti S, Gissler M, Mentula M, Heikinheimo O. Is teenage pregnancy an obstetric risk in a welfare society? A population-based study in Finland, from 2006 to 2011. BMJ Open. 2013;3(8):e003225. (7.8%) or the United Kingdom2424. Kenny LC, Lavender T, McNamee R, O'Neill SM, Mills T, Khashan AS. Advanced maternal age and adverse pregnancy outcome: evidence from a large contemporary cohort. PLoS One. 2013;8(2):e56583. (7.7%), as well as in emerging countries like India2525. Mahavarkar SH, Madhu CK, Mule VD. A comparative study of teenage pregnancy. J Obstet Gynaecol. 2008;28(6):604–7. (10%). However, this rate was lower than those verified in other Brazilian studies, such as those conducted in 2002 in Rio Grande do Norte2626. Azevedo GD, Freitas Júnior RA, Freitas AK, Araújo AC, Soares EM, Maranhão TM. Effect of maternal age on perinatal outcomes]. Rev Bras Ginecol Obstet. 2002;24(3):181–5. Portuguese. (25.3%) and in 1997/98 in São Luís2727. Simões VMF, Silva AAM, Bettiol H, Lamy-Filho F, Tonial SR, Mochel EG. Characteristics of adolescent pregnancy, Brazil]. Rev Saúde Pública. 2003;37(5):559–65. Portuguese. (29.7%). Our data thus show a decrease in teenage pregnancy rates compared with previous studies carried out in Brazil. Nevertheless, they also reveal that these rates are still high in this population, highlighting the percentage of pregnant women aged 12 to 15 years (2.23%) compared, for instance, with the Finnish2323. Leppälahti S, Gissler M, Mentula M, Heikinheimo O. Is teenage pregnancy an obstetric risk in a welfare society? A population-based study in Finland, from 2006 to 2011. BMJ Open. 2013;3(8):e003225. study, where only 0.09% of the pregnant women belonged to this age group.

The percentage of mothers at an advanced age (>35 years) was 5.9%. This ratio is lower than the proportion found in developed countries, such as the United Kingdom2424. Kenny LC, Lavender T, McNamee R, O'Neill SM, Mills T, Khashan AS. Advanced maternal age and adverse pregnancy outcome: evidence from a large contemporary cohort. PLoS One. 2013;8(2):e56583. (16.6%) or Norway1919. Wang Y, Tanbo T, Abyholm T, Henriksen T. The impact of advanced maternal age and parity on obstetric and perinatal outcomes in singleton gestations. Arch Gynecol Obstet. 2011;284(1):31–7., where one third (33.4%) of pregnant women are older than 35 years, and higher than that found in São Luís in 1997/982727. Simões VMF, Silva AAM, Bettiol H, Lamy-Filho F, Tonial SR, Mochel EG. Characteristics of adolescent pregnancy, Brazil]. Rev Saúde Pública. 2003;37(5):559–65. Portuguese. (4.2%). Data indicating that an increased number of women delay motherhood have been confirmed by several Brazilian1212. Andrade PC, Linhares JJ, Martinelli S, Antonini M, Lippi UG, Baracat FF. Perinatal results in pregnant women with more than 35 years: a controlled study]. Rev Bras Ginecol Obstet. 2004;26(9):697–701. Portuguese.,1313. Senesi LG, Tristão EG, Andrade RP, Krajden ML, Oliveira Junior FC, Nascimento DJ. Neonatal morbidity and mortality related to pregnant women at the age of 35 and older, according to parity]. Rev Bras Ginecol Obstet. 2004;26(6):477–82. Portuguese.and worldwide1414. Huang L, Sauve R, Birkett N, Fergusson D, van Walraven C. Maternal age and risk of stillbirth: a systematic review. CMAJ. 2008;178(2):165–78.,1515. Jahromi BN, Husseini Z. Pregnancy outcome at maternal age 40 and older. Taiwan J Obstet Gynecol. 2008;47(3):318–21. studies.

The preterm birth rate was 12.1% in this investigation. A Norwegian study of 6,619 pregnant women conducted between 2004 and 20071919. Wang Y, Tanbo T, Abyholm T, Henriksen T. The impact of advanced maternal age and parity on obstetric and perinatal outcomes in singleton gestations. Arch Gynecol Obstet. 2011;284(1):31–7. had a preterm birth rate of 9.6%. A cohort with more than 200,000 women from 2004 to 2008 in the United Kingdom2424. Kenny LC, Lavender T, McNamee R, O'Neill SM, Mills T, Khashan AS. Advanced maternal age and adverse pregnancy outcome: evidence from a large contemporary cohort. PLoS One. 2013;8(2):e56583. encountered a 7.54% preterm birth rate. Among the Brazilian studies, 2,160 pregnant women in Hospital do Servidor Público de São Paulo,in the period from 2000 to 20031212. Andrade PC, Linhares JJ, Martinelli S, Antonini M, Lippi UG, Baracat FF. Perinatal results in pregnant women with more than 35 years: a controlled study]. Rev Bras Ginecol Obstet. 2004;26(9):697–701. Portuguese. presented a preterm birth rate of 11.7%, while a group of 2,429 subjects in the city of São Luís in 1997/982727. Simões VMF, Silva AAM, Bettiol H, Lamy-Filho F, Tonial SR, Mochel EG. Characteristics of adolescent pregnancy, Brazil]. Rev Saúde Pública. 2003;37(5):559–65. Portuguese. found one of 12.6%.

Regarding IUGR, we found a 16.2% rate. This value is similar to that seen in a study conducted with Mexican pregnant women between 2009 and 20102828. Zepeda-Monreal J, Rodríguez-Balderrama I, Del Carmen Ochoa-Correa E, de la O-Cavazos ME, Ambriz-López R. Risk factors associated with intrauterine growth restriction in newborns attended in a university hospital]. Rev Med Inst Mex Seguro Soc. 2012;50(2):173–81. Spanish. (13.5%). In Brazil, studies carried out in São Paulo1212. Andrade PC, Linhares JJ, Martinelli S, Antonini M, Lippi UG, Baracat FF. Perinatal results in pregnant women with more than 35 years: a controlled study]. Rev Bras Ginecol Obstet. 2004;26(9):697–701. Portuguese. and Rio Grande do Norte2626. Azevedo GD, Freitas Júnior RA, Freitas AK, Araújo AC, Soares EM, Maranhão TM. Effect of maternal age on perinatal outcomes]. Rev Bras Ginecol Obstet. 2002;24(3):181–5. Portuguese. achieved IUGR rates of 10.0 and 7.1%, respectively. The high proportion of this outcome in the current study seems to be also associated with the poor socioeconomic conditions of the studied population, as previously demonstrated by Matijasevich et al.2929. Matijasevich A, Victora CG, Lawlor DA, Golding J, Menezes AM, Araújo CL, et al. Association of socioeconomic position with maternal pregnancy and infant health outcomes in birth cohort studies from Brazil and the UK. J Epidemiol Community Health. 2012;66(2):127–35..

Despite several reports in the literature demonstrating the increased risk of preterm birth and IUGR in women at either end of their reproductive lives, this subject remains controversial22. Schempf AH, Branum AM, Lukacs SL, Schoendorf KC. Maternal age and parity-associated risks of preterm birth: differences by race/ethnicity. Paediatr Perinat Epidemiol. 2007;21(1):34–43.55. Mariotoni GG, Barros Filho AA. Peso ao nascer e características maternas ao longo de 25 anos na Maternidade de Campinas. J Pediatr (Rio J). 2000;76(1):55–64.,77. Bettiol H, Barbieri MA, Gomes UA, Wen LY, Reis PM, Chiaratti TM, et al. Atenção médica à gestação e ao parto de mães adolescentes. Cad Saúde Pública. 1992;8(4):404–13.99. Debras E, Revaux A, Bricou A, Laas E, Tigaizin A, Benbara A, et al. Obstetric and neonatal outcomes of adolescent pregnancies: a cohort study in a hospital in Seine-Saint-Denis France]. Gynecol Obstet Fertil. 2014;42(9):579–84. French.. Currently, however, it is thought that living conditions and health of the pregnant woman, particularly the quality of prenatal care and delivery, are more important than age99. Debras E, Revaux A, Bricou A, Laas E, Tigaizin A, Benbara A, et al. Obstetric and neonatal outcomes of adolescent pregnancies: a cohort study in a hospital in Seine-Saint-Denis France]. Gynecol Obstet Fertil. 2014;42(9):579–84. French.1111. 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. J Nutr. 2007;137(2):447–52..

We obtained rates of preterm births of the early (18.6%) and late adolescents (14.9%) significantly higher than that of the Control Group (20 to 35 years; 11.1%). This trend is consistent with data from several studies performed in Brazil2626. Azevedo GD, Freitas Júnior RA, Freitas AK, Araújo AC, Soares EM, Maranhão TM. Effect of maternal age on perinatal outcomes]. Rev Bras Ginecol Obstet. 2002;24(3):181–5. Portuguese. and in other countries2323. Leppälahti S, Gissler M, Mentula M, Heikinheimo O. Is teenage pregnancy an obstetric risk in a welfare society? A population-based study in Finland, from 2006 to 2011. BMJ Open. 2013;3(8):e003225.,3030. Mukhopadhyay P, Chaudhuri RN, Paul B. Hospital-based perinatal outcomes and complications in teenage pregnancy in India. J Health Popul Nutr. 2010;28(5):494–500.,3131. Lao TT, Ho LF. The obstetric implications of teenage pregnancy. Hum Reprod. 1997;12(10):2303–5.. Nonetheless, the actual preterm births rates reported for these age groups (adolescents and controls) vary considerably among these studies, possibly as a result of the different characteristics of the studied populations.

It is noteworthy that the strength of the association between early adolescence and preterm birth (OR=1.6) was greater than that observed between late adolescence and this outcome (OR=1.3). In addition to all of the social problems associated with teenage pregnancy, these data suggest that biological immaturity has a greater influence on this age group than on older adolescents. Ribeiro et al.88. Ribeiro ERO, Barbieri MA, Bettiol H, Silva AAM. Comparação entre duas coortes de mães adolescentes em município do Sudeste do Brasil. Rev Saúde Pública. 2000;34(2):136–42. mentioned that adolescents aged 13 to 17 years had a 2-fold higher rate of LBW and one nearly to this of preterm birth regarding adolescents aged 18 to 19 years in a cohort studied in 1994 in Ribeirão Preto, Brazil, thus corroborating the results of the current study.

IUGR rates for both early (22.3%) and late adolescences (19.1%) were higher than that of the Control Group (15.4%), although this difference was not significant. Studies that have attempted to associate teenage pregnancy with increased IUGR rates are contradictory; in fact, some of them attributed it to demographic and socioeconomic factors that were not actually controlled99. Debras E, Revaux A, Bricou A, Laas E, Tigaizin A, Benbara A, et al. Obstetric and neonatal outcomes of adolescent pregnancies: a cohort study in a hospital in Seine-Saint-Denis France]. Gynecol Obstet Fertil. 2014;42(9):579–84. French.1111. 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. J Nutr. 2007;137(2):447–52.. An Australian study concluded that the risk of maternal morbidity is significantly increased by social disadvantage3232. Lindquist A, Noor N, Sullivan E, Knight M. The impact of socioeconomic position on severe maternal morbidity outcomes among women in Australia: a national case-control study. BJOG. 2014 Epub ahead of print]..

Preterm birth was more prevalent among pregnant women of advanced age (14.3%) compared with those aged 20 to 35 years; however, the statistical significance was borderline (OR=1.4; 95%CI 0.99–1.96; p = 0.05). Regarding IUGR, a small but not significant difference was found between the group of women older than 35 years (16.1%) and the Control Group (15.4%; OR=1.3; 95%CI 0.9–1.8; p = 0.13). These findings do not concur with several previous studies that reported higher rates of adverse obstetric outcomes in pregnant women of advanced age3333. Seoud MA, Nassar AH, Usta IM, Melhem Z, Kazma A, Khalil AM. Impact of advanced maternal age on pregnancy outcome. Am J Perinatol. 2000;19(1):1–8.3535. Suzuki S, Miyake H. Obstetric outcomes in nulliparous women aged 35 and over with singleton pregnancies conceived by in vitro fertilization. Arch Gynecol Obstet. 2008;277(3):225–7.. However, similar to our findings, other studies have found no association between advanced maternal age and adverse obstetric outcomes1919. Wang Y, Tanbo T, Abyholm T, Henriksen T. The impact of advanced maternal age and parity on obstetric and perinatal outcomes in singleton gestations. Arch Gynecol Obstet. 2011;284(1):31–7.,3636. Bianco A, Stone J, Lynch L, Lapinski R, Berkowitz G, Berkowitz RL. Pregnancy outcome at age 40 and older. Obstet Gynecol. 1996;87(6):917–22.,3737. Callaway LK, Lust K, McIntyre HD. Pregnancy outcomes in women of very advanced maternal age. Aust N Z J Obstet Gynaecol. 2005;45(1):12–6., suggesting that without risk factors such as hypertension and/or diabetes, the course and outcome of the pregnancy of women of advanced age could be similar to those of younger women. Consequently, advanced maternal age alone cannot be associated with the studied perinatal outcomes (preterm birth and IUGR). Risk factors like hypertension and diabetes, which were more prevalent in pregnant women of advanced age, may instead be the factors responsible for the adverse outcomes. These findings indicate that minimizing the risks associated with these adverse outcomes will require improved prenatal care for women at either end of their reproductive life.

This study has some limitations. The cross-sectional design of the study did not allow more robust conclusions about the risk of the studied outcomes, indicating only the associations. Furthermore, although the number of studied patients was appropriate, extremes of the age categories were not represented by optimal numbers of individuals; some of the borderline associations could therefore potentially reach significance in larger samples.

The present research makes an important contribution to the discussion about the influence of maternal age on two studied perinatal outcomes because this was a population-based study, and the sample size, despite the problems mentioned, was larger than those of most studies on this subject. The work also adds essential information on a subject that is poorly understood, particularly in the Northeastern region of Brazil.

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  • Programa de Pós-graduação em Saúde Coletiva da Universidade Federal do Maranhão – UFMA – São Luís (MA), Brazil.

Publication Dates

  • Publication in this collection
    21 Nov 2014
  • Date of issue
    Dec 2014

History

  • Received
    20 Sept 2014
  • Accepted
    15 Oct 2014
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