Thirty year trends in a large Irish obstetric cohort.

To evaluate sequential trends in respect of parity, maternal age, gestation at delivery and birthweight in a large cohort of the national birth total during the period 1968 to 1998. Retrospective review of obstetric variables in six biennial cohorts at six yearly intervals, among mothers delivering at the National Maternity Hospital (NMH), Dublin. Where feasible comparisons have been made with contemporary national data. During the thirty year period, total NMH births varied between 11 and 14% of the Irish total. The proportions of primigravidae and grandmultiparae have increased by 15% and decreased by 21% respectively. There has been a shift in the predominant childbearing age group from 25-29 years to the 30-34 years. The proportion of teenage pregnancies has altered very little but births to women over 40 years has declined sharply from 6.0% to 3.0%. Births outside marriage have increased from 5% to 29%. Although, there has been a trend towards increasing average birthweight, no increase was observed in infants exceeding 4.5Kg. Total infants weighing under 1.5Kg have more than doubled. National birth statistics generally reflected NMH trends but with an apparent year time lag.