Severe acute maternal morbidity in multiple pregnancies: a nationwide cohort study

BACKGROUND: Adverse neonatal outcomes in multiple pregnancies have been documented extensively, in particular those associated with the increased risk of preterm birth. Paradoxically, much less is known about adverse maternal events. The combined risk of severe acute maternal morbidity in multiple pregnancies has not been documented previously in any nationwide prospective study.

OBJECTIVE: To assess the risk of severe acute maternal morbidity in multiple pregnancies in a high-income European country and identify possible risk indicators.

STUDY DESIGN: In a population-based cohort study including all 98 hospitals with a maternity unit in the Netherlands, pregnant women with severe acute maternal morbidity were included in the period 1(st) August 2004 until 1(st) August 2006. We calculated the incidence of severe acute maternal morbidity in multiple pregnancies in the Netherlands using the Netherlands Perinatal Registry. Relative risks (RR) of severe acute maternal morbidity in multiple pregnancies compared to singletons were calculated. To identify possible risk indicators we also compared age, parity, method of conception, onset of labour and mode of delivery for multiple pregnancies using the Netherlands Perinatal Registry as reference.

RESULTS: 2552 cases of severe acute maternal morbidity were reported during the two-year study period. Among 202 multiple pregnancies (8.0%), there were 197 twins (7.8%) and five triplets (0.2%). The overall incidence of severe acute maternal morbidity was 7.0 per 1000 deliveries, 6.5 and 28.0 per 1000 for singletons and multiple pregnancies respectively. The relative risk of severe acute maternal morbidity compared to singleton pregnancies was 4.3 (95% confidence interval [95% CI] 3.7-5.0) and increased to 6.2 (95% CI 2.5-15.3) in triplet pregnancies. Risk indicators for developing severe acute maternal morbidity in women with multiple pregnancies were age of ≥40 (RR 2.5 95% CI 1.4-4.3), nulliparity (RR 1.8, 95% CI 1.4-2.4), use of assisted reproductive techniques (RR 1.9, 95% CI 1.4-2.5), and non-spontaneous onset of delivery (RR 1.6, 95% CI 1.2-2.1). No significant difference was found between mono- and dichorionic twins (RR 0.8, 95% CI 0.6-1.2).

CONCLUSIONS: Women with multiple pregnancies in the Netherlands have a more than four times elevated risk of sustaining severe acute maternal morbidity as compared to singletons.