Can We Predict Preterm Delivery Based on the Previous Pregnancy?

Abstract

(1) Background: Preterm deliveries (PTD, <37 gestational weeks) which occur in 5–18% of deliveries across the world, are associated with immediate and long-term offspring morbidity, as well as high costs to health systems. Our aim was to identify risk factors during the first pregnancy ending at term for PTD in the subsequent pregnancy. (2) Methods: A retrospective population- based nested case−control study was conducted, including all women with two first singleton consecutive deliveries. Women with PTD in the first pregnancy were excluded. Characteristics and complications of the first pregnancy were compared among cases, defined as women with PTD in their second pregnancy, and the controls, defined as women delivering at term in their second pregnancy. A multivariable logistic regression model was used to study the association between pregnancy complications (in the first pregnancy) and PTD (in the subsequent pregnancy), while adjusting for maternal age and the interpregnancy interval. (3) Results: A total of 39,780 women were included in the study, 5.2% (n = 2088) had PTD in their second pregnancy. Women with PTD, as compared to controls (i.e., delivered at term in second pregnancy), were more likely to have the following complications in their first pregnancy: perinatal mortality (0.4% vs. 1.0%), small for gestational age (12.4% vs. 8.1%), and preeclampsia (7.6% vs. 5.7%). In the multivariable model, after adjusting for maternal age, interpregnancy interval and co-morbidities, having any one of these first pregnancy complications was independently associated with an increased risk for PTD (adjusted OR = 1.44; 95%CI 1.28–1.62), and the risk was greater if two or more complications were diagnosed (adjusted OR = 2.09; 95%CI 1.47–3.00). These complications were also risk factors for early PTD (<34 gestational weeks), PTD with a systematic infectious disease in the background, and possibly with spontaneous PTD. (4) Conclusions: First pregnancy complications are associated with an increased risk for PTD in the subsequent pregnancy. First pregnancy, although ending at term, may serve as a window of opportunity to identify women at risk for future PTD.

The role of confounding in the association between pregnancy complications and subsequent preterm birth: a cohort study

“…More recently, researchers have turned their attention to the subsequent risk of preterm birth from complications when the first birth is term. [5][6][7] Finding similar results to ours, a study from Norway reported a two-fold increase in the risk of preterm birth when the previous births were term with at least one complication (pre-eclampsia, placental abruption, smallfor-gestational age, stillbirth or neonatal mortality), compared with an uncomplicated first term birth. 6 Consistent with our study, the authors also found little evidence for confounding by known demographic and lifestyle factors.…”

“…One pathway that explains the association between complicated term birth and subsequent preterm birth is that the complications can also reoccur 8,9 . Recurrence has been well established for pre‐eclampsia, 10 placental abruption 11 and small‐for‐gestational age, 12 complications linked to ischaemic placental diseases, 13 with these complications acting as risk factors for preterm birth 5–7 . Another more complex explanation is that each complication is associated with an increased risk of other complications, 8,14 which is supportive of the hypothesis of shared underlying mechanisms 8 .…”

“…[1][2][3]7,11,15,16,[42][43][44][45] There is consistent evidence for the recurrence of preterm birth, 1-3 most notably when the previous preterm birth occurred with early-onset pre-eclampsia. 7,43 One study reported an increased risk for recurrent placental abruption after a term first birth, compared with preterm birth, 44 another study reported almost three-fold higher odds of preterm birth (compared with a term birth) after a small-for-gestational preterm birth, 42 and a study reported that previous all-cause infant death (up to 365 days post-birth) was associated with a two-fold increase in the risk of a subsequent preterm birth. 45 Only two studies considered the reverse associations **The e-values for the effect estimates are the minimum strength of association on the risk ratio scale that an unmeasured confounding factor would need to have with both the exposure and the outcome to fully explain away the association between preterm birth in the first pregnancy and complications in the second term pregnancy.…”

“…20,21 However, the shared causal pathway is not necessarily biological. Environmental confounding factors such as socio-economic status, income, age, education and body mass index have previously been identified as risk factors for pregnancy complications 7 and preterm birth. 22 If environmental risk factors and underlying biological mechanisms that cause complications of pre-eclampsia, placental abruption, smallfor-gestational age and perinatal death are shared with preterm birth, these associations would persist from pregnancy to pregnancy.…”

“…4 The assumption that a term birth in first pregnancy can be considered sufficient to imply a reduced risk for a future preterm birth has been refuted by recent studies. [5][6][7] These studies reported that term first births complicated by pre-eclampsia, placental abruption, smallfor-gestational age, stillbirth or neonatal death were associated with elevated risks of subsequent preterm birth, leading the authors to conclude that there are likely shared underlying pathological mechanisms persisting from pregnancy to pregnancy. [5][6][7] One pathway that explains the association between complicated term birth and subsequent preterm birth is that the complications can also reoccur.…”