Intrauterine fetal death: classification and risk factors : A case-control study of sociodemographic, clinical and thrombophilic risk factors

Background: Stillbirth or intrauterine fetal death (IUFD) is a severe and difficult event for the parents and occurs in approximately five of 1000 births in high-income countries. Understanding of causes and recognition of risk factors is essential for preventive measures, counseling of parents, surveillance of health care and comparison both nationally and internationally.Objectives: To estimate the incidence of stillbirths in a Norwegian population, classify according to cause of death, investigate socio-demographic, clinical and thrombophilic risk factors and to evaluate variations in risk estimates by different control selection. Methods: 377 women with IUFD after 22 gestational weeks at two university hospitals in the Oslo area, in the period 1990 to 2003, were classified according to the Cause Of Death and Associated Conditions (CODAC) classification of perinatal deaths. They were compared with two different control-groups for the identification of socio-demographic and clinical risk factors. A subsample of 105 cases and 262 controls comprised the study population for acquired and inherited thrombophilic risk factors. Results: The incidence of stillbirths was 4.1 per 1000 deliveries. The majority (68%) had placental pathology as a main cause of death or as an associated condition. Small for gestational age (SGA) and placental abruption were strongly associated with IUFD, but hypertensive disorders were moderate risk factors if not mediated through SGA. Other risk factors were of low prevalence and of limited importance in the prevention of IUFD. Risk factors differed according to cause, apart from smoking and SGA that were risk factors in all causal groups. Lupus anticoagulant was associated with a history of IUFD, although probably confined to women with multiple positivity for antiphospholipid antibodies. The prothrombin gene G20210A polymorphism was also associated with IUFD, most prominent in the group of placental causes.