Objective: To investigate the relationship between maternal preterm birth and fetal growth in one generation and perinatal mortality of twin offspring in the next generation.
Design: Population-based cohort study.
Setting: The Medical Birth Registry of Norway from 1967 to 2008.
Population: Linked generational data with 9426 mother-twin pair units.
Methods: Twin offspring were linked to their mothers by means of the unique national identification numbers.
Main outcome measures: Perinatal mortality in twin offspring.
Results: The twin prevalence was not dependent on the mother's gestational age at birth, but increased with increasing birthweight in term mothers. Maternal gestational age was strongly and inversely associated with a risk of perinatal death in one or both of her twin offspring. Compared with term mothers, preterm mothers born at 27-31 and 32-34 weeks had relative risks (RRs) for perinatal loss of 3.83 [95% confidence interval (CI), 1.56-9.36] and 2.41 (95% CI, 1.29-4.50), respectively. This effect was even stronger after the use of assisted reproductive technologies (ART), with a significant interaction between maternal gestational age and ART (P = 0.03). Further, term mothers with birthweight-by-gestational age Z-scores of -2 or less had more than twice the risk of a perinatal loss in their twin offspring relative to mothers with the most favourable birthweight Z-scores (1-1.99) [RR, 2.42 (95% CI, 1.37-4.29)].
Conclusions: Women born preterm had an increased risk of perinatal mortality in their twin offspring, particularly after ART treatment. The same was true for women who were growth restricted at term. A twin pregnancy is a high-risk pregnancy in general, but even more so if the mother herself was born preterm or was growth restricted at birth.
© 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2011 RCOG.