Changes in fetal death during 40 years-different trends for different gestational ages: a population-based study in Norway.

OBJECTIVE

To study changes in gestational-age-specific fetal death risks during a 40-year period.

DESIGN

Register-based observational study.

SETTING

The Medical Birth Registry of Norway.

POPULATION

All pregnancies after 16 weeks of gestation in Norway from 1967 to 2006 (n = 2, 182, 756).

METHOD

Changes in fetal death risk since 1967-1971 (reference) were estimated as absolute risks (rates) and relative risks (RR) in ongoing pregnancies at the following gestational weeks; 16-22, 23-29, 30-36 and 37-43.

MAIN OUTCOME MEASURES

Fetal death.

RESULTS

In all pregnancies lasting longer than 22 weeks, the fetal death rate decreased during 1967-2006. The greatest decline was in term pregnancies (37-43 weeks) from 10.8 to 3.3 fetal deaths per 1000 at risk (crude RR 0.35; 95% CI 0.31-0.38) comparing 1967-1971 with 2002-2006. In pregnancies at 30-36 weeks the fetal death rate declined from 4.5 to 1.1 per 1000 (crude RR 0.23; 95% CI 0.21-0.26). At 23-29 weeks, the rate declined from 2.8 to 1.3 per 1000 (crude RR 0.46; 95% CI 0.40-0.52). An opposite trend was observed at early gestation (16-22 weeks) with an increase from 1.7 to 3.4 fetal deaths per 1000 ongoing pregnancies (crude RR 2.05; 95% CI 1.84-2.27). Adjustments for maternal age, parity, multiple pregnancies, paternal age and pre-eclampsia did not significantly alter the estimated associations.

CONCLUSION

Since 1967 the risk of fetal death has been reduced by almost 70% in pregnancies lasting longer than 22 weeks; however, at 16-22 weeks of gestation there was an increase in risk. The causes of this increase should be further explored because it may be attributed to an increase in early delivery caused by the increased proportion of women being treated with cervical cone excision before pregnancy.