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Cohorts are studies also known as longitudinal studies, which are based on the identification of a group of individuals and on their follow-up over a period of time. The term cohort was created for referring to groups of soldiers who marched together in Roman legions during the Roman Empire.
In 2004, all 4,231 children born in Pelotas joined one of the largest and most comprehensive child health follow-up studies in the world: the 2004 Cohort. This project stands out as the largest in developing countries, providing valuable insights into health from birth.
The 2004 Cohort is the third cohort study conducted by the Center for Epidemiological Research and the Postgraduate Program in Epidemiology at the Federal University of Pelotas (UFPel). The history of these studies includes the 1982 Cohort, which followed 5,914 babies, the 1993 Cohort, with 5,249 children, and the 2015 Cohort, which included 4,275 newborns. Each study has not only recorded health at birth and in early years but also continues to follow these individuals throughout their lives to analyze how birth conditions influence long-term health.
With the participation of approximately 20,000 people, the cohorts document significant changes in population health, contributing to the improvement of healthcare from childhood. The data obtained have been essential for the formulation of effective public policies.
One notable impact of these studies is the reduction in infant mortality in Pelotas, from 20 to 12.3 per thousand births between 2004 and 2007, directly resulting from the researchers’ recommendations. These actions have saved countless lives and underscore the ongoing relevance and importance of birth cohorts in enhancing public health.
Each of the 4,231 children born in Pelotas in 2004 plays a vital role in health research. This group has been crucial in shaping public health policies aimed at improving the health of the population in Brazil and in Pelotas. The research also holds significant importance globally.
Data from the 2004 Cohort have demonstrated that well-planned, evidence-based measures can address major public health challenges, such as reducing infant mortality. In 1982, when studies began in Pelotas, infant mortality was high, with 36 deaths per thousand live births. Since then, researchers have focused on preventing these deaths, finding that many could be avoided.
Over the 22 years of follow-up, various actions have been implemented in the city based on research findings, including efforts to reduce premature births and campaigns to promote breastfeeding. The result has been a significant decline in infant mortality. In 2004, the rate dropped to 19.4 deaths per thousand births, and three years later, to 12.3. These improvements were made possible by the collaboration of thousands of mothers who, after giving birth, answered numerous questions from researchers and allowed their babies to undergo examinations. Additionally, these mothers permitted researchers to visit their homes multiple times over the years to monitor their children’s development. The time and effort of the mothers, children, and researchers have resulted in valuable scientific knowledge that benefits everyone.
In 2024, the 2004 Cohort celebrates 20 years of partnership, with continued collaboration from the majority of participants residing in Pelotas and many others who have relocated. In 2026, we will conduct another follow-up and look forward to another successful phase in this life-long research project for both participants and researchers.
Births
4,231 live births in hospitals in the city.
Mother’s Age
From 12 to 46 years old
18.9% of mothers were under 20 years old.
Maternal age increased with family income, with mothers from higher-income groups being 4.3 years older than mothers from lower-income groups.
Sex of the Newborns
48.1% girls
51.9% boys
Delivery
45.2% of women had a cesarean section.
A cesarean section is an abdominal operation performed to deliver the baby when normal delivery is not possible or safe.
Cesarean Section
64.5% of wealthier women had cesarean sections.
It was observed that women at higher risk received less medical attention and care during pregnancy and childbirth compared to low-risk women.
Birth Weight
According to the World Health Organization (WHO), birth weight is the most important factor in infant survival. Babies with low birth weight (less than 2.5 kg) are at greater risk of illness and death compared to babies with adequate weight. Out of 4,231 children, 424 were born with low birth weight.
Breastfeeding
97.2% of children were breastfed.
56% were being breastfed at six months of age.
It is known that non-breastfed children have a 30% higher risk of death in the first year of life. The World Health Organization (WHO) recommends that all children be breastfed for at least six months and continue up to two years of age.
Breastfeeding has increased significantly over 22 years:
Smoking
27.6% of mothers smoked during pregnancy.
Babies born to smoking mothers had a twice as high rate of low birth weight compared to babies born to non-smoking mothers. Low birth weight is known to be one of the main causes of newborn mortality.
Mortality
Of the 4,231 newborns, 82 died in their first year of life.
Infant mortality was 4.4 times higher among the poorest compared to the richest.
The highest risk of death occurs until the child reaches one year old. Therefore, health care during this phase should be reinforced by parents and doctors.
Mortality among children has decreased over 22 years:
Even with the decrease in mortality rates, researchers continue to work towards further reducing the number of child deaths. It is known that reducing preterm births and breastfeeding are important factors in preventing death in the first year of life.
Child Development
More developed children were stimulated in the following ways:
Studies have shown that, in addition to the practices listed, games, play, riddles, and small plays stimulate children’s development in their early years.
Data at 18 Years of Age
Evaluated:
3,489 participants, representing 85% of the original cohort.
Obesity
Proportion of individuals with obesity: 15.5%
Obesity, defined as a Body Mass Index (BMI) >30 kg/m², is associated with numerous health issues, including reduced mobility, bone diseases, diabetes, cardiovascular conditions, and cancer. Maintaining a healthy weight through balanced nutrition, regular physical activity, and adequate sleep is crucial for improving overall quality of life. BMI: weight/(height)²
Smoking
Had a habit of smoking at least once a week: 12.6%
Active smokers: 8.6%
Smoking is linked to over 50 diseases, including cardiovascular and respiratory conditions, and cancer. Smokers may experience up to a 20-year reduction in life expectancy compared to non-smokers.
Alcohol Consumption
Alcohol consumption two or more times a week: 12%
Alcohol use can lead to dependence and increase the risk of liver diseases, cardiovascular conditions, and cancer. It may also contribute to depression, anxiety, decreased work capacity, and traffic accidents. Responsible alcohol consumption promotes better quality of life and personal well-being.
Work
Had worked at least once: 60.5%
Working in 2022: 35.2%
Sleep Duration
Average sleep duration on weekdays:
6.8 hours for boys
7.1 hours for girls
On weekends:
8.2 hours for boys
8.8 hours for girls
Young adults aged 18 to 25 should aim for 7 to 9 hours of sleep per night, according to the National Sleep Foundation. Adequate sleep is essential for physical, emotional, and mental health, playing a key role in recovery and overall well-being.
Sleep Quality
Sleep Quality Rated as Good or Very Good: 82.9%
Sleep Quality Rated as Poor or Very Poor: 17.1%
Poor sleep quality and sleep deprivation are associated with obesity, diabetes, hypertension, cardiovascular diseases, and mental health disorders.
Blood Pressure
A blood pressure reading above 140/90 mmHg indicates elevated blood pressure, a chronic condition that increases the risk of premature death. Modifiable risk factors, such as high intake of salt and trans and saturated fats, alcohol consumption, smoking, and physical inactivity, contribute significantly to the development of hypertension.
Modifiable risk factors such as a diet high in salt, trans and saturated fats, alcohol consumption, smoking, and physical inactivity contribute to the development of hypertension.
The Pelotas Birth Cohort of 2004 was established to build upon the findings of the Pelotas cohorts of 1982 and 1993, creating a comprehensive group of 15,000 individuals to examine changes in social and epidemiological health patterns.
Methodology of the 2004 Cohort
This cohort includes all children born in Pelotas between January and December 2004, whose mothers lived in the urban area of the city. To enhance comparability with previous cohorts, the 2004 Cohort also incorporated newborns from the Jardim América neighborhood in Capão do Leão. A total of 4,231 children were enrolled, a smaller number compared to previous cohorts.
Initial Follow-ups
– **Perinatal and 3 months:** Initial interviews with mothers within the first 24 hours postpartum, followed by home visits at 3 months.
– **12 months:** A follow-up home visit to gather data on the family’s socioeconomic status, maternal mental health, and child development.
– **24 and 48 months:** Home visits focusing on child development.
– **6 years:** This assessment, conducted at 72 months, took place at the Center for Epidemiological Research (CPE), equipped with state-of-the-art technology. Evaluations included health measures, dietary assessments, body composition, lifestyle, quality of life for children and their mothers, as well as cognitive and mental health tests.
Adolescent Follow-ups
– **11 years (2010-2011):** Measurements of anthropometry, body composition, and physical activity, along with questionnaires on general and maternal mental health, and adolescent nutrition.
– **15 years (2019-2020):** Due to the COVID-19 pandemic, approximately half of the participants were interviewed. This follow-up included health assessments and hair sample collection for cortisol analysis.
– **17 years (2021):** A sub-study to assess the impact of COVID-19 on the lives of the youth, with additional hair cortisol collection.
Follow-up at 18 Years
In 2022, follow-up consisted of two phases: home interviews with the young adults and their mothers, followed by clinical assessments at the CPE, including health measurements, blood collection, and analysis of physical activity.
Scientific Production and Resources
The research conducted with the 2004 Cohort has led to numerous scientific publications in open-access journals. The instruments and questionnaires utilized are available to the scientific community.
The 2004 Cohort exemplifies both continuity and innovation in health research, contributing to substantial advancements in understanding social and epidemiological patterns in Brazil.
+55 (53) 3284 – 1300
ppgepi@ufpel.edu.br
Rua Marechal Deodoro, 1160 – 3° Piso
Bairro Centro – Pelotas, RS
Cep: 96020-220 – Caixa Postal 464