Abstract
Background: We aimed to explore the association of the number, order, gestational age and type of prior PTB and the risk of preterm birth (PTB) in the third delivery in women who had three consecutive singleton deliveries. Methods: A retrospective cohort study of all women who had three consecutive singleton births at a single medical center over a 20-year period (1994–2013). The primary outcome was PTB (<37 weeks) in the third delivery. Results: 4472 women met inclusion criteria. The rate of PTB in the third delivery was 4.9%. In the adjusted analysis, the risk of PTB was 3.5% in women with no prior PTBs; 10.9% in women with prior one PTB only in the first pregnancy; 16.2% in women with prior one PTB only in the second pregnancy; and 56.5% in women with prior two PTBs. A similar trend was observed when the outcome of interest was spontaneous PTB and when the exposure was limited to prior spontaneous or indicated PTB. Conclusions: In women with a history of PTB, the risk of recurrent PTB in subsequent pregnancies is related to the number and order of prior PTBs. These factors should be taken into account when stratifying the risk of PTB.
Highlights
Prematurity is considered as the leading cause of neonatal morbidity and mortality [1,2,3] with approximately 11% and 2% of viable pregnancies resulting in delivery prior to 37 and 34 weeks of gestation, respectively [1,4]
The lack of distinguishing between indicated and spontaneous preterm birth (PTB) [13,16] and the unknown parity at the time of the index pregnancy [16] can limit the interpretation of the results of prior studies regarding the effect of obstetrical history on future risk for PTB
The primary exposure was a history of PTB < 37 weeks in the first 2 births, and was classified into four groups based on the number and order of prior PTBs: (1) No prior PTBs (Term-Term group, which served as reference); (2) One PTB only in the first pregnancy (PTB-Term group); (3) One PTB only in the second pregnancy (Term-PTB group); and (4) PTBs in both the first and second pregnancies (PTB-PTB group)
Summary
Prematurity is considered as the leading cause of neonatal morbidity and mortality [1,2,3] with approximately 11% and 2% of viable pregnancies resulting in delivery prior to 37 and 34 weeks of gestation, respectively [1,4]. Spontaneous preterm birth (PTB) is considered a final common pathway of many biological mechanisms that vary between individuals [4] These etiologic pathways are still yet to be elucidated [4,5]. Over the last few decades, there has been an increase in the rate of indicated PTB, mainly in the late preterm (34–36 weeks of gestation) period without a clear understanding on their effects on future deliveries [1,17]. The lack of distinguishing between indicated and spontaneous PTB [13,16] and the unknown parity at the time of the index pregnancy [16] can limit the interpretation of the results of prior studies regarding the effect of obstetrical history on future risk for PTB. These factors should be taken into account when stratifying the risk of PTB
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