CHANGES IN RISK-FACTORS FOR UNFAVORABLE PREGNANCY OUTCOME AMONG SINGLETONS OVER 20 YEARS

Objectives. To examine the change in the prevalence and relative effec t of pre-pregnancy risk factors for low birthweight and/or stillbirth and/or neonatal mortality over a period of twenty years. Design. Two p rospectively collected one year birth cohorts. Setting. The two northe rnmost administrative districts of Finland. Patients. A birth cohort f or 1966 comprising 11905 singleton births and a cohort for 1985-86 con taining a further 9247. Main outcome measures. Risk factors for poor p regnancy outcome. Results. In twenty years the prevalence of low birth weight infants among singletons decreased from 4.2% to 3.1% and that o f stillbirths and neonatal deaths from 2.4% to 0.9%. The impact of sin gle marital status decreased and while maternal age <19 years was not an independent risk factor, the age greater than or equal to 35 years related more to poor pregnancy outcome. The proportion of multiparous women was halved but multiparity had a protective influence on pregnan cy outcome meanwhile the impact of primiparity decreased markedly. In spite of more effective health education, the prevalence of heavy smok ers was 4 times higher in the 1980s as compared with the 1960s, and it s impact on adverse outcomes increased, with odds ratio (OR) 1.72 (con fidence interval(CI) 1.14-2.61) in 1966 and OR2.15(CI 1.61-2.88) in 19 85-86. The number of mothers with a previous low birthweight baby was halved but the impact of low birth weight was still great in the latte r cohort (OR 2.47; CI 1.64-3.71). The impact of an earlier stillbirth and/or neonatal death increased significantly, with an OR 1.53 (CI 1.1 0-2.14) in 1966 and OR 2.95 (CI 1.81-4.81) in 1985-86, but the number of mothers concerned was halved from that in 1966. Conclusions. The pr evalence of pregnancies with an adverse outcome decreased markedly, as did the prevalence of many of the risk factors. The proportion of gre ater than or equal to 35 years old parturients and of heavy smokers in creased. The impact of primiparity decreased, while that of a previous poor pregnancy outcome increased. Identification of pregnancies with a risk of a peer outcome as assessed from pre-pregnancy factors has no t improved in these twenty years, especially where primiparous parturi ents are concerned.