About the CLHNS
Conducted by a team of researchers from the United States and the Philippines, the Cebu Longitudinal Health and Nutrition Survey is part of an ongoing study of a cohort of Filipino women who gave birth between May 1, 1983, and April 30, 1984. The CLHNS was originally conceptualized as a study of infant feeding patterns, particularly the overall sequencing of feeding events (i.e., of both milk and non-milk items), the various factors affecting feeding decisions at each point in time, and how different feeding patterns affect the infant, mother, and household. The idea was to study these topics within as natural a setting as possible and to analyze how infant feeding decisions by the household interact with various social, economic, and environmental factors to affect health, nutritional, demographic, and economic outcomes. During the period of project design from 1981 to 1983, the focus was expanded so that more issues related to selected health, demographic, and nutritional outcomes could be addressed. The selected outcomes were birth weight and gestational age; infant feeding, growth, morbidity, and survival; maternal diet and nutritional status; maternal labor supply and time allocation; and child spacing. A number of intermediate behaviors, such as medical care and water and sanitation utilization patterns, have also been the subject of focused measurement and analysis.
Field work for the CLHNS ’83-’84 was conducted from May 1983 through April 1984. A single stage cluster sampling procedure was used to randomly select 33 communities or barangays (17 urban, 16 rural) from the Metropolitan Cebu area. The barangays, which contained about 28,000 households, were completely surveyed in late 1982 and again in early 1983 to locate all pregnant women. Women of the selected barangays who gave birth between May 1, 1983, and April 30, 1984, are included in the sample. A baseline interview was conducted among 3,327 women during the 6th to 7th month of pregnancy so that all births, including preterm births, could be identified. Subsequent surveys took place immediately after birth, then at bimonthly intervals for 24 months. From the baseline sample, there were 3,080 nontwin live births. Approximately 2,600 households were studied intensively for the full 2 years. Each survey collects detailed health, nutrition, demographic, and socioeconomic data.
Individual, household, and community data were collected during the baseline survey. Detailed community surveys of health and family planning facilities, health personnel (modern and traditional), and commercial establishments selling infant foods were undertaken on a periodic basis. A birth information survey was conducted to obtain information about the delivery and to determine birth weight, gestational age (including clinical assessment of low birth weight infants, infants of mothers with diabetes, and infants of mothers with no last menstrual period data). The bimonthly longitudinal surveys obtain dietary, morbidity, anthropometry, infant care, family planning, and related data. Water quality tests were conducted repeatedly over an 18-month period for all types of barangay and household water sources, and an analysis of household sources of water consumed by infants was obtained for a subsample of infants. The same subsample was used to study the etiology of diarrhea. A detailed description of this stage of the field work is provided in the Survey Procedures document.
Index children have now been followed through adolescence and into young adulthood, and the CHLNS is tracking their offspring as they begin to have children themselves. The objective is to have a high quality, longitudinal intergenerational study of health. For the mothers, the objective is to follow mothers to the end of their reproductive careers to understand the effects of reproductive cycles on maternal health and nutritional status and to track the development of chronic disease risk factors and aging-related disabilities.
The 1991-92 follow-up study included 2,399 women who had answered the baseline and birth information surveys of the original CLHNS. They provided reproductive histories, health histories, information on dietary intake and nutritional status, and related demographic and socioeconomic data. For each index child, information on diet, health history, nutritional status, schooling, and anthropometry was collected. In addition, anthropometric data for all younger siblings of the index children were collected. A total of 2,260 children, with an average age of 8.5 years, were surveyed in this follow up study. The 1991-92 study also added a focus on entry into school, and administered a non-verbal intelligence test developed for use in the Philippines by George Guthrie. For a detailed description of the data available from this survey, see the Introduction to 1991 document.
The 1994-95 follow-up study of women and children from the original CLHNS was undertaken beginning in October of 1994 and was completed in October of 1995. Approximately 2,300 women from the original CLHNS sample were located and interviewed. In addition a new sample of about 500 women between the ages of 15 and 25 were recruited. The resulting total sample of 2800 women represented ages from 15 to 55. Basic questionnaire modules from the original and 1991 follow-up surveys were administered to ensure continuity with previous rounds of data collection. Additional information on family planning, women’s health status, intra-household relationships, school achievement, non-verbal intelligence, vision, and hearing were added.
For each child, information is available on diet, health history (major illnesses, immunizations, hospitalizations), nutritional status (based on anthropometry), schooling, and IQ. The 1994 survey added tests achievements tests of Cebuano and English reading skills, and mathematics.
The 1998-99 survey added a focus on adolescent reproductive health and sexual behavior, and measured physical activity using questionnaires as well as an objective measure (Caltrac). In addition, a subgroup of the sample participated in a clinical study which collected fasting blood samples and saliva. An additional pilot study examined the effects of typhoid immunization on thymic function and immune status. Blood pressure measurements in the adolescents and mothers were added to this survey. Among the mothers, memory tests and questionnaire modules on physical functioning were added.
In The 2002 survey, the index “children” were young adults, and data were collected on their schooling outcomes and entry into the labor force. The study continued to monitor health and anthropometry. Reproductive histories of the young adults were added.
In The 2005 survey, the CLHNS added collection of biomarkers in the full sample. After an overnight fast, blood samples were taken for extraction of DNA, and plasma was stored for the analysis of cardiovascular disease risk factors. The study continued to track health and physical functioning of the mothers and schooling, work, and reproductive outcomes in the offspring.
In 2007, a limited tracking survey was conducted to maintain contact with participants and to collect reproductive histories on the index young adults so that their offspring could be tracked as well. Tracking surveys are ongoing.
In 2009, both the female and male index children were interviewed. Index children have now been followed through adolescence and into young adulthood, and the CHLNS is tracking their offspring as they begin to have children themselves. The objective is to have a high quality, longitudinal intergenerational study of health. For the mothers, the objective is to follow mothers to the end of their reproductive careers to understand the effects of reproductive cycles on maternal health and nutritional status and to track the development of chronic disease risk factors and aging-related disabilities.
Since its inception, the CLHNS has had numerous funding sources for data collection and analysis, including the National Institutes of Health (R01-HD19983A, R01-HD18880, P01-HD28076, R01-HD23182, R01-TW05596, R01-HL085144, R01-DK078150, R01-HD054501, R03TW008133) the Nestle Coordinating Center for Nutrition Research, Wyeth International, The Ford Foundation, The US National Academy of Science, The World Health Organization, The US Agency for International Development (via grants from Wellstart International, the International Center for Research on Women, Family Health International, MEASURE), The Asian Development Bank, The World Bank, The Thrasher Research Fund, The Mellon Foundation, Nestle Research Foundation, and The Carolina Population Center.