Fertility rates and perinatal outcomes of adolescent pregnancies: a retrospective population-based study

ABSTRACT Objective: analyze trends in fertility rates and associations with perinatal outcomes for adolescents in Santa Catarina, Brazil. Methods: a population-based study covering 2006 to 2013 was carried out to evaluate associations between perinatal outcomes and age groups, using odds ratios, and Chi-squared tests. Results: differences in the fertility rate among female adolescents across regions and time period were observed, ranging from 40.9 to 72.0 per 1,000 in mothers aged 15-19 years. Adolescents had fewer prenatal care appointments than mothers ≥20 years, and a higher proportion had no partner. Mothers aged 15-19 years were more likely to experience preterm birth (OR:1.1; CI:1.08-1.13; p<0.001), have an infant with low birthweight (OR:1.1; CI:1.10-1.15; p<0.001) and low Apgar score at 5 minutes (OR:1.4; CI:1.34-1.45; p<0.001) than mothers ≥20 years, with the odds for adverse outcomes greater for those aged 10-14 years. Conclusion: this study provides evidence of fertility rates among adolescents remaining higher in regions of social and economic deprivation. Adolescent mothers and their infants more likely to experience adverse perinatal outcomes. Nurses, public health practitioners, health and social care professionals and educators need to work collaboratively to better target strategies for adolescents at greater risk; to help reduce fertility rates and improve outcomes.


Introduction
National fertility rates among adolescents are commonly used as an indicator for children and young people's health. While there has been a decline in the birth rate globally in recent years, pregnancy in adolescence remains a public health concern. The global birth rate, or age-specific fertility rate, for mothers aged 15 to 19 from 2007 to 2012 has been reported as 50 per 1,000. At national levels, higher rates are consistently reported for developing nations in sub-Saharan Africa; however, rates for Brazil are consistently higher than the global rates, with a rate of 68 in 1,000 reported in 2012, which is among the highest rates reported in Latin America and the Caribbean (1) . The World Health Organization (WHO) also reports that half of all births to adolescent mothers occur in just seven countries, Brazil being one of these (2) . Adolescent pregnancy has been recognized as a major contributing factor to maternal and child mortality, morbidity and poverty (3) . Epidemiological studies indicate that adolescent pregnancies lead to a greater proportion of infants being born preterm and/or with low birth weight, which in turn have been associated with higher mortality rates (4)(5)(6)(7) . Low socioeconomic conditions, risky lifestyle behaviors, poor adherence to prenatal care and biological immaturity have also been suggested as possible explanations for adverse obstetric and perinatal outcomes in this group (4)(5)8) .
With the Millennium Development Goals 4 (reducing child mortality) and 5 (improving maternal health), public health strategies for tackling teenage pregnancy rates have been promoted in both developed and developing nations (9-10) . However, regional differences may persist and better targeting vulnerable populations may result in greater improvements. Consequently, evaluating the trends in fertility rates at a national and regional level is vital to comprehend any progress made and to indicate targets for the future.
The aim of this study is to understand the characteristics and health-related outcomes of live births to teenage mothers in comparison to adult mothers by analysing trends in age-specific fertility rates and associations with selected perinatal outcomes across one  Age-specific fertility rates were calculated as a ratio, defined by the United Nations (UN) * as the annual number of births to women of a specified age or age group per 1,000 women in that age group. Data for the State of Santa Catarina were collected for the years 2006-2013 inclusive. However, data by region were unavailable for the year 2013, due to the absence of regional data for the denominator. Hence, age-specific fertility rates at the regional level were calculated for the years 2006-2012. Data on maternal characteristics included age (grouped as 10-14 years, 15-19 years, or ≥20 years of age), years of formal education (grouped as <8 or ≥8 years) and marital status, which was categorized as with partner (married or co-habiting) or without partner (single, widowed, separated or divorced). Pregnancyrelated variables included the number of prenatal appointments attended (<7 or ≥7 appointments) and type of delivery (vaginal birth or caesarean section).
Infant outcomes included gestational age at birth (<37 or ≥37 weeks), birth weight (<2500 grams or ≥2500 grams) and Apgar at 5 minutes, categorized as scores ≤7 or 8 to 10. The Apgar score establishes the clinical condition of all newborn infants immediately after delivery, regardless of the delivery mode, with a high score indicating good physical condition (8) . Aggregate data were collected on all live births by health region

Data analysis
Population statistics relating to age-specific fertility rates among adolescents are most frequently reported for those aged 15 to 19 years. As such, data were analyzed by age groups 10 to14 years and 15 to 19 years.
Age-specific fertility rates for female adolescents in the Odds Ratios (OR) and 95% Confidence Intervals (CI) were calculated to measure the level of association between specified age groups and perinatal outcomes.
Chi-squared tests for statistical significance were also performed. Data were analyzed using electronic support. This research did not involve direct recruitment and consent of human subjects, as secondary analysis was conducted on data collected from publicly available sources that contain anonymized data. In Table 1 66.6% (n=73,992), respectively. For women aged ≥20 years, this figure was 40.4% (n=230,534).

In
In    (6) . The high number of adolescent pregnancies has previously been attributed to a failure of public health policies in the prevention of unplanned pregnancies and in sexual and reproductive health education reaching young people (13) .
Many adolescents are deterred from engaging in the preference, prevention and promotion approach primary health care systems approach. As such, greater effort is needed in targeting appropriate strategies and effective interventions to adolescents in regions that are falling behind the State and/or Brazilian average (14) .
Complications in teenage pregnancies have previously been associated with adverse social conditions, low levels of education, marital status, lack of family support and, above all, inadequate prenatal care (13) . The findings from this paper support this evidence. Effective prenatal care is able to detect infectious diseases that have the potential for vertical transmission and a range of adverse conditions that may impair the health of the mother and fetus, such as malaria, HIV, rubella, syphilis and hepatitis. Above all, it is a simple task during a prenatal visit to check maternal and fetal vital signs, estimate gestational risks and assist in preventing adverse outcomes (15) . Prenatal care is a valuable tool for monitoring the health of the mother, as well as monitoring the on-going development of the fetus, and has been associated with lower rates of preterm birth and a reduction in infants of low birth weight (13) . Prenatal care for all adolescents therefore needs to commence early in gestation to ensure that early identification of risk takes place and that any follow-up actions required are taken (16) .
In this population-based study, the incidence of preterm birth (<37 gestation weeks) was higher among mothers aged 10 to 14 year olds than those aged 15 to 19 years and 20 years old or more, which is similar to figures reported in developing countries (12) .
It should also be noted that the incidence of maternal the issue of preventing maternal near miss (4)(5)18) (13,19) , placing the State of Santa Catarina in a slightly better context than most low-and middle-income countries. Nevertheless, the birth weight of infants in developed and developing countries remains a major factor affecting neonatal morbidity and mortality, and is an important indicator of public health (6,8) . Likewise, nutrition and lifestyle habits post-conception (use of alcohol, tobacco, drug misuse, exposure to infections, such as malaria and HIV) also influence fetal growth and development, as well as the duration of pregnancy (16) .
Women with unfavorable socioeconomic conditions often have infants with low birth weight, which in turn has been linked to poor nutrition and unhealthy lifestyle habits (5,16) .
Low birth weight may result in a risk to the survival and development of the infant. In addition, children with teenage mothers are in greater need of a social support network, which is not always available. Thus, the growth and development of these children, with follow-up health checks through attendance at well-baby clinics, is paramount. This requires nurses to take care of the adolescent mother/child dyad. The health care network has to be prepared to offer adequate support to those clients of greater vulnerability, both during attendance at the health services and at home. Adolescents are women in the process of discovering their sexuality and are not always prepared for motherhood (10,(13)(14)16) .
With regard to delivery, the preferred mode is vaginal, as long as there are no medical indications for a caesarean section, which may include two or more previous caesareans, fetal macrosomia or shoulder dystocia (20) . This study found that the prevalence of caesarean sections in pregnant women younger than 20 years old was lower than those aged 20 years or more 10-15% of all births (21) . New regulations are being enforced in 2015 in Brazil (22) , in an attempt to reduce the universally high rate of caesarean sections, by ensuring that pregnant women are informed of the risks, with the ultimate aim of reducing rates and creating a shift in the culture to informed choice and decision making by mothers.
In the early assessment of infant health, the Apgar score is an important tool to monitor the physical condition of newborns. According to the findings in this study, an Apgar score <7 occurred in 3% of births to adolescent mothers, which is similar to national data.
A cohort study recently conducted in Brazil reported significant associations between neonatal mortality and birth weight, gestational age at birth, a low Apgar score at 5 minutes, the use of mechanical ventilation and congenital malformations (23) . However, the use of the Apgar score in preterm infants has been reported to be inconsistent and any assumptions with respect to the predictive value of the Apgar score for infant mortality should also take into account a range of other factors, including social and economic conditions (24) .
Nevertheless, previous research aimed at assessing causal links between a range of maternal and pregnancyrelated variables and infant Apgar scores reported associations between the frequency of prenatal care and an Apgar score of less than seven (13) . The authors provided evidence that appropriate prenatal care halves the risk of an unsatisfactory Apgar score (13)  many of the associated risks or social losses they may experience in becoming a mother (18,26) .
In terms of study limitations, it should be noted that in calculating the fertility rates among adolescents aged 10-14 years, the denominator data related to all female adolescents aged 10-14 years in the State and each respective region. Consequently, the rates observed are likely to be an underestimation of the true fertility rate in this cohort. It would be more appropriate to employ an estimate of exposure to childbearing by females aged 10-14 years as the denominator. However, these data were unavailable. The reader should also reflect on the issue of reporting fertility rates among adolescents, instead of the rate of teenage pregnancy. This figure would undoubtedly be higher, as it would include not only all pregnancies that resulted in a live birth, but also those that resulted in a spontaneous miscarriage, termination of pregnancy or stillbirth. Understanding any disparities across regions in relation to the differences between pregnancy rates and fertility rates is difficult without the routine collection and dissemination of these data. Nevertheless, fertility rates are useful as a proxy measure at a local level to obtain a better understanding of trends, in order to target effective interventions and evaluate their efficacy.

Conclusions
The findings from this current study raise awareness In addition, a network of specialized support and care to pregnant adolescents, which incorporates reproductive, prenatal, psychological and social support and care, may contribute to the reduction of obstetric and fetal risks.