Effects of maternal age, parity, and smoking on the risk of stillbirth.
OBJECTIVE
To examine the effects of advanced maternal age, nulliparity, and smoking on risk of stillbirth as gestation advances, and to explore possible clinical mediators of these effects.


METHODS
A population based cohort study.


METHODS
Sweden, 1983 to 1989.


METHODS
All singleton pregnancies of 28 weeks gestation or greater in Nordic citizens at least 20 years old (n = 638,242).


METHODS
Crude and adjusted risks of stillbirth; gestational age specific risks of stillbirth.


RESULTS
Older women (35 years or older), smokers, and nulliparas had elevated risks of stillbirth. The elevated stillbirth risk in smokers was eliminated when women with intrauterine growth retardation, placental abruption, and placenta previa were excluded from the analysis. However, the higher risks in older women and nulliparas persisted even when the analysis excluded women with hypertension, diabetes, placental complications, or growth retardation. Over the course of the third trimester, the age related risk of stillbirth increased, the smoking related risk decreased, and the higher risk in nulliparas showed no clear trend with gestational age.


CONCLUSIONS
The association between smoking and stillbirth is explained entirely by the higher incidence of growth retardation and placental complications in smokers. The clinical mediators of the associations of maternal age and parity with stillbirth remain unexplained. Gestational age is an important modifier of the effects of advanced maternal age and smoking on stillbirth risk.
Raymond
E G
EG
Division of Epidemiology, Statistics, and Prevention Research, National Institute of Child Health and Human Development, National Institutes of Health, Rockville, Maryland.
Cnattingius
S
S
Kiely
J L
JL
D000022:Abortion, Spontaneous / Q000453:epidemiology / Q000209:etiology*; D000328:Adult; D015331:Cohort Studies; D005260:Female; D005313:Fetal Death / Q000453:epidemiology / Q000209:etiology*; D005317:Fetal Growth Retardation / Q000209:etiology; D005865:Gestational Age; D006801:Humans; D008423:Maternal Age; D016017:Odds Ratio; D010298:Parity; D011159:Population Surveillance; D011247:Pregnancy; D018566:Pregnancy, High-Risk; D012044:Regression Analysis; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D013548:Sweden / Q000453:epidemiology