Different pathways for preterm birth between singleton and twin pregnancies: a population-based registry study of 481 176 nulliparous women

ObjectiveTo explore the contribution of pregnancy-related complications on the prevalence of extremely, very and late preterm births in singleton and twin pregnancies. To study the risk of spontaneous preterm birth in twin pregnancies compared with singleton pregnancies. DesignPopulation-based registry study. SettingMedical birth registry of Norway and Statistics Norway. PopulationNulliparous women with singleton (n = 472 449) or twin (n = 8727) births during 1999-2018. MethodsPrevalence rates of pregnancy-related complications for extremely, very and late preterm birth in twin and singleton pregnancies were calculated with 95% confidence intervals. Multivariable logistic regression was applied to assess odds ratios for preterm birth, adjusted for obstetric and socio-economic factors. Main outcome measuresExtremely preterm (<28(+0) weeks of gestation), very preterm (28(+0)-33(+6) weeks of gestation) and late preterm (34(+0)-36(+6) weeks of geatation) birth. ResultsPreterm birth was significantly more prevalent in twin pregnancies than in singleton pregnancies in all categories: all preterm (54.7% vs 6.1%), extremely preterm (3.6% vs 0.4%), very preterm (18.2% vs 1.4%) and late preterm (33.0% vs 4.3%) births. Stillbirth, congenital malformation and pre-eclampsia were more prevalent in twin pregnancies than in singleton pregnancies, but the prevalence of complications differed in the three categories of preterm birth. Pre-eclampsia was more prevalent in singleton than in twin pregnancies ending in extremely and very preterm birth. The adjusted odds of spontaneous preterm live birth were between 19- and 54-fold greater in twin pregnancies than in singleton pregnancies. ConclusionsSingleton and twin pregnancies seem to have different pathways leading to extremely, very and late preterm birth.

Automated summary

This population-based registry study explored the impact of pregnancy-related complications on the prevalence of preterm births in singleton and twin pregnancies. The results showed significantly higher rates of preterm birth in twin pregnancies compared to singleton pregnancies across all categories. Twin pregnancies also had higher prevalence of stillbirth, congenital malformation, and pre-eclampsia. The adjusted odds of spontaneous preterm birth in twin pregnancies were 19 to 54 times greater than in singleton pregnancies.