Role of prenatal care in preterm birth and low birthweight in Portugal.
BACKGROUND
It remains unclear if benefits of prenatal care can be attributed to the amount and content of care or to uncontrolled risk factors that might also affect its use. This study was designed to evaluate the independent association between prenatal care adequacy and adverse pregnancy outcomes, measured either as the occurrence of preterm birth or low birthweight.


METHODS
We studied 3734 single liveborn infants. Information on mothers' use of prenatal care, and demographic, anthropometric, behavioural, clinical and obstetric characteristics were obtained through questionnaire. Prenatal care was classified as inadequate, intermediate or adequate based on Kessner's Adequacy of Prenatal Care Index. To estimate the association of adequacy of prenatal care and the defined outcomes, both crude and adjusted odds ratios (OR) and 95 per cent confidence intervals (95 per cent CI) were calculated by means of unconditional logistic regression.


RESULTS
Adequate and intermediate (compared with inadequate) prenatal care was significantly associated with a lower risk of preterm (OR = 0.20, 95 per cent CI 0.12-0.32, and OR = 0.35, 95 per cent CI 0.23-0.54, respectively) or low birthweight (OR = 0.23, 95 per cent CI 0.15-0.35, and OR = 0.31, 95 per cent CI 0.20-0.46, respectively). After adjusting for maternal age, social class, marital status, complications of pregnancy and type of hospital, the risk of preterm delivery remained significantly lower for women receiving adequate (OR = 0.18, 95 per cent CI 0.11-0.28) or intermediate care (OR = 0.35, 95 per cent CI 0.23-0.54). Adjusted for maternal body mass index, marital status, cigarette smoking, pregnancy weight gain and complications, type of hospital, newborn sex and gestational age, a significant decreased risk of low birthweight remained for infants of women with adequate (OR = 0.39, 95 per cent CI 0.23-0.65) or intermediate care (OR = 0.47, 95 per cent CI 0.29-0.76).


CONCLUSIONS
Our findings show that in a population with free access to prenatal care, the quantitative adequacy of prenatal care has an independent effect on pregnancy outcome, whether assessed through the occurrence of preterm births or low birthweight infants.
Department of Hygiene and Epidemiology, University of Porto Medical School, Portugal.
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D000328:Adult; D005260:Female; D006801:Humans; D007226:Infant Mortality; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007234:Infant, Premature; D008019:Life Style; D008297:Male; D011174:Portugal / Q000453:epidemiology; D011247:Pregnancy; D011248:Pregnancy Complications; D011295:Prenatal Care / Q000706:statistics & numerical data*; D012307:Risk Factors; D012959:Socioeconomic Factors