Infant Mortality among Twins from the Pelotas 2004 and 2015 Birth Cohorts

Author(s): Iná S Santos, Neiva Cristina J Valle, Mariangela F Silveira, Alicia Matijasevich, Andréa D Bertoldi, Marlos Domingues, Gabriel Santana, Ivete Maria Kreutz, Fernando CF Barros.

Objective: To describe the prevalence of multiple pregnancies and compare first- and second-born twins to each other and to singletons, in terms of infant mortality.

Methods: The 2004 and 2015 Pelotas Birth Cohorts are population-based studies conducted in Pelotas, South Brazil. A monitoring system was assembled to detect all deaths of cohort participants in the first year of life. Infant Mortality Rate (IMR):1000 live births (LB) and its components (neonatal and post-neonatal mortality rates) were calculated.

Results: Among 4,187 pregnancies in 2004 and 4,220 in 2015, respectively, 42 (1.0%) and 56 (1.3%) were multiple. Eighty-four twins were born alive in 2004 and 111 in 2015. The majority of twin pregnancies failed to reach 37 weeks (61.9% in 2004 and 82.2% in 2015). Prevalence of twin births < 34 weeks of gestation more than doubled from 2004 (19.0%) to 2015 (42.1%) (p=0.03). In the 2004 cohort, there were 79 infant deaths, three of which were twins, and in the 2015 cohort, among the 57 deaths, five were of twins. In the 2004 cohort there was no difference in IMR between twins and singletons. In the 2015 cohort, IMR in first-born twins was similar to that of singletons, whereas among second-born twins, the IMR was six times higher than in singletons (75.4:1,000 LB versus 12.5:1000 LB).

Conclusion: While improvements in medical care may have led to improved survival among infants born at less than 34 weeks, these infants are still at increased risk of dying before reaching one year of age.

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