About 27,000 babies are born prematurely - or before 37 weeks' gestation - across Australia each year, with preterm birth the leading cause of death and morbidity in children up to five years of age in the developed world.
Until recently, a first birth at full term was considered a reduced risk for a preterm delivery in the next pregnancy. However, there is emerging evidence that a complicated first pregnancy, regardless of whether the baby was delivered early or at full term, increases the subsequent risk of a baby being born prematurely.
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Our Curtin University study examined birth records of more than 125,000 Western Australian women who experienced two consecutive singleton births between 1998 and 2015.
The findings showed a strong link between preterm birth and pregnancies complicated by pre-eclampsia, a serious pregnancy condition that is usually characterised by high blood pressure, protein in the urine and severe swelling.
When both pregnancies were complicated by pre-eclampsia, the risk of a subsequent preterm birth increased 10-fold after an initial term birth and 17-fold when the first birth was preterm, compared to women who had an uncomplicated first pregnancy.
The study also found there was a three-fold higher risk of women experiencing a subsequent case of pre-eclampsia after a preterm birth in the first pregnancy that was not complicated by pre-eclampsia.
The main pregnancy complications examined included pre-eclampsia, placental abruption (the detachment from the wall of the womb), small-for-gestational age and perinatal death (a stillbirth or a neonatal death in the first 28 days).
Having any of the four complications in their first pregnancy puts women at an increased risk of a preterm birth in their next pregnancy, regardless of whether that first birth ended at full term or preterm. Likewise, women whose first pregnancy ended in a preterm delivery were at an increased risk for each pregnancy complication in the second pregnancy.
The findings of this study will help clinicians to better identify women who are at an increased risk of a either a preterm birth or complications in their subsequent pregnancies. Further research is now needed to reveal the specific pathways that explain these strong links between pregnancy complications and preterm births, whether they be genetic, pathological, and behavioural or other recurrent issues.
- Jennifer Dunne, Curtin University's School of Population Health.
