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.