Characteristic of Preterm Delivery and Low Birthweight among 113,994 Infants in Alberta: 1994-1996

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ABSTRACT

This study examined the impact of infant and maternal factors on preterm delivery and low birthweight (LBW) in Alberta between January 1, 1994 and December 31, 1996. Data on 113,994 births were collected from vital statistics registration birth data. Logistic regression models for preterm and LBW delivery suggested the key risk factors were multiple and still birth (odds ratios >22.0). Other characteristics included female gender, birth defects, nulliparous women, maternal age 35 and greater, unmarried, history of abortion, maternal smoking, maternal street drug use, and having less than 4 prenatal visits (odds ratios 0.86-2.54). Interactions between smoking and alcohol, and smoking and parity were noted. Efforts to improve the currently low rates (8.2%) of smoking cessation during pregnancy are required. Social, economic and medical factors associated with delayed childbearing and birth outcomes should be investigated.

ABREGE

L'etude porte sur l'influence des caracteristiques de la mere et du nourrisson sur les accouchements prematures et l'insuffisance de poids at la naissance (IPN) en Alberta entre le 1^sup er^ janvier 1994 et le 31 decembre 1996. Nous avons recueilli des donnees sur 113 994 naissances a partir des inscriptions aux registres d'etat civil. Selon nos modeles de regression logistique pour les accouchements prematures et l'IPN, les principaux facteurs de risque auraient ete les accouchements multiples ou de bebes morts-nes (ratios d'incidence approches >22,0). Les autres caracteristiques etaient le sexe feminin, les anomalies congenitales, la nulliparite et le fait pour la mere d'avoir 35 ans ou plus, d'etre celibataire, d'avoir deja avorte, de fumer, d'utiliser des drogues illicites ou d'avoir effectue moins de quatre visites prenatales (ratios d'incidence approches 0,86-- 2,54). Nous avons constate des interactions entre le tabagisme et l'alcool, et entre le tabagisme et le rang des naissances. Il faudrait s'efforcer d'ameliorer les faibles taux de renoncement au tabac durant la grossesse (8,2 % actuellement) et etudier les facteurs sociaux, economiques et medicaux associes a la procreation tardive et a l'issue de la grossesse.

Despite the identification of potential risk factors for preterm and low birth-- weight (LBW) delivery, their incidences have increased in some areas.1 Risk factors that have been identified for premature delivery and/or LBW include maternal smoking, alcohol consumption, street drug use,2-4 as well as maternal age and multiple birth.1,5

Preterm and LBW infants are at an increased risk of neonatal mortality and morbidity (including visual and hearing deficits, speech delay, reduced growth, and developmental delays), increased hospitalizations and use of physician services.5-10

The purpose of this population-based study was to investigate the determinants of preterm and LBW delivery in Alberta. A population-based study provides a sufficient sample size for determining the independent contribution of modifiable and non-- modifiable risk factors towards infant outcome. This sample size enhances generalizability, which has been a problem in previous studies on preterm and LBW delivery.11

METHODS

All 113,994 births in the Province of Alberta between January 1, 1994 and December 31, 1996 were included in the study. Data were obtained from the Physician Notice of Live or Still Birth and Newborn Record (PNOB) which, by law, is completed on all births. Information on infant factors such as birth outcome (liveborn, stillborn), gestational age (best estimate as derived from the maternal last menstrual period and antenatal ultrasound examination), multiple birth, gender, birthweight (weight in grams in the delivery room), and visible birth defects is included on the PNOB. Information on parity, gravida, frequency of prenatal visits, marital status, smoking, alcohol consumption, and street drug use is also collected. …