Our aim was to compare the fetal mortality rate (FMR), early neonatal
mortality rare (ENMR) and perinatal mortality rate (PMR) of post-term
and term births. 2) to examine trends in the incidence and perinatal m
ortality rates of post-term and term births. We used data from Spanish
Perinatal Mortality Survey of 1980, 1986, 1989 and 1992. The data inc
lude 40.863 post-term births (42 weeks and over) and 517,060 term birt
hs (37-41 weeks). Perinatal mortality rates of postterm and term birth
s were compared. The incidence of post-term births was 7.3%. The relat
ive risk (RR) of FMR for post-term compared to term births was 1.1 (95
% confidence interval [CI] 0.9-1.3), of ENMR was 1.6 (95% CI 1.4-2.0)
and of PMR was 1.3 (95% CI 1.1-1.5). From 1980 to 1992 there was a sig
nificant reduction in the incidence of post-term births (8.1% vs 5.0%)
. in the FMR (4.5/1000 vs 1.9/1000). ENMR (4.3/1000 vs 2.0/1000) and P
MR (8.7/1000 vs 3.9/1000) of post-term births. There was no significan
t difference in the FMR between post-term and term in each year studie
d. Post-term births had a significantly higher ENMR and PMR than term
births in 1980, and they were equivalent from 1983 to 1992. The incide
nce of post-term births, its FMR, ENMR and PMR have been significantly
reduced during the whole period studied.