Maternal birth characteristics and perinatal mortality in twin offspring. An intergenerational population-based study in Norway, 1967-2008.

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.