Ultrasound estimates of gestational age among perinatally demised: a population-based study

BACKGROUND: Correct estimation of gestational age may improve the quality of obstetric care. We hypothesize that significant differences between traditional and alternative estimates by ultrasound are evident among perinatal deaths. METHODS: Population-based case series with data linkage between autopsy records and The Medical Birth Registry of Norway, including perinatally demised singletons who were examined by autopsy and post-mortem radiography, having antenatal estimates of gestational age both by the calendar method, as calculated from the first day of the last menstrual period preceding the pregnancy (GAlmp), and by mid-second-trimester ultrasound (GAus), N = 380. The main outcome measure was the distribution of GAlmp and GAus within weight strata. RESULTS: Mean GAus was 1 week less than mean GAlmp (t-test, p < 0.001). The degree of apparent growth restriction manifest after death, as expressed by both birthweight and by post-mortem radiographic measurements, was fairly well correlated with the degree of downward adjustment of age by ultrasound in the early second trimester (Pearson's correlation, r = - 0.599, p < 0.001). The degree of discrepancy between the ultrasound and the calendar methods was associated both with placenta findings (Kruskal-Wallis test, chi2 = 20.95, p = 0.007) and with the main cause of death (Kruskal-Wallis test, chi2 = 27.65, p = 0.004). CONCLUSION: Among infants who died perinatally, gestational age seemed to be systematically downward adjusted by mid-second-trimester screening ultrasound, particularly among those who were the most growth retarded at the time of death.