Risk factors for unexplained antepartum fetal death in Norway 1967-1998.
OBJECTIVE
To relate unexplained antepartum fetal death with maternal and fetal characteristics in order to identify risk factors.


METHODS
Population-based study based on records of 1,676,160 singleton births with gestational age > or =28 weeks. Unexplained antepartum fetal death was defined as fetal death before labour without known fetal, placental, or maternal pathology.


RESULTS
Although unexplained fetal mortality in general declined from 2.4 per 1000 births in 1967-1976 to 1.6 in 1977-1998, the proportion among all fetal deaths increased from 30% to 43% during the same period of observation. Unexplained fetal death occurred later in gestation than explained. From 39 weeks of gestation, the risk increased progressively to 50/10,000 in women aged > or =35 years and <10/10,000 in women <25 years. In birth order > or =5, the risk was particularly high after 39 weeks of gestation. For birth weight percentile 2.5-9.9 and > or =97.5, unexplained fetal death was four and three times more likely to occur, respectively. We found an additive effect of maternal age and birth weight percentile 2.5-9.9. Women with less than 10 years education had higher risk than women with 13 years or more (OR=1.6). Weaker associations were observed with female gender, unmarried mothers, and winter season.


CONCLUSIONS
Unexplained antepartum fetal death occurred later in gestation than explained and was associated with high maternal age, multiparity, low education, and moderately low and high birth weight percentile. The increased risk in post-term pregnancies and the additive effect of maternal age and birth weight percentile 2.5-9.9 suggests that older women would benefit from monitoring of fetal growth.
Rasmussen
Svein
S
Medical Birth Registry of Norway, Locus of Registry Based Epidemiology, Haukeland University Hospital, University of Bergen, Armauer Hansen Building, N-5021 Bergen, Norway. svein.rasmussen@mfr.uib.no
Albrechtsen
Susanne
S
Irgens
Lorentz M
LM
Dalaker
Knut
K
Maartmann-Moe
Helga
H
Vlatkovic
Ljiljana
L
Markestad
Trond
T
D001724:Birth Weight; D005260:Female; D005313:Fetal Death / Q000453:epidemiology* / Q000209:etiology; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008423:Maternal Age; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D011159:Population Surveillance; D011247:Pregnancy; D018566:Pregnancy, High-Risk; D012042:Registries / Q000706:statistics & numerical data; D012307:Risk Factors