Introduction
Preterm birth (PTB) is in quantity and severity one of the most important cause of neonatal mortality and morbidity.1,2 An important challenge in the prevention of PTB is the recognition of patients at risk, because effective preventive measures such as cervical cerclage and the administration of progesterone are available.3
Previous spontaneous preterm birth (sPTB) has proven to be an important risk factor for recurrent PTB, yet the lower limit of the gestational age of prior birth at which the recurrent risk is increased is not well defined.4–6 The widely used WHO definition of PTB distinguishes between extremely preterm (<28 weeks), very preterm (28-32 weeks) and moderate or late preterm (32-37 weeks), but is limited by lacking a lower limit of gestational age. The upper limit of 37 weeks is widely used across various countries, but the lower limit varies between 20, 22 and 28 weeks for respectively the USA7, Europe8 and China9. Therefore, there is no general consensus on the gestational age demarcation between miscarriage and extreme PTB. This complicates a clear assessment of which patients are at risk for subsequent or recurrent PTB, especially for patients with previous birth around 20 weeks. Yet, especially in these patients, early recognition of risk factors will contribute to early intervention in the management of preventing PTB.
Objective: In this study we will assess the recurrence risk of total PTB per gestational age group, following sPTB between 16+0- 27+6 weeks. In addition, we will assess the role of interpregnancy interval in this association.