Carried out by researchers at the University of Bergen and the Norwegian Institute of Public Health in Norway along with the National Institute of Environmental Health Sciences and Duke University in the USA, the new study looked at data gathered from 302,192 women in Norway’s Medical Birth Registry.
The researchers looked at a possible link between five complications in the first pregnancy and the risk of preterm delivery, which is before 37 weeks, in the next pregnancy.
The complications included pre-eclampsia (abnormally high blood pressure and too much protein in the urine), placental abruption (when the placenta comes away from the womb), stillbirth, neonatal death (in the first 28 days) and having a small baby (small for gestational age).
The findings, published Thursday in The BMJ, showed that even after taking into account other potentially influencing factors, such as mother’s age, pre-pregnancy weight, and smoking status, women who carried to full term but who experienced any of the five complications appeared to have a substantially increased risk of preterm delivery in their next pregnancy.
More specifically, the risk of preterm delivery in second pregnancy was 3% for women with none of the five term complications, 6% after experiencing pre-eclampsia, 7% after term placental abruption, 13% after term stillbirth, 10% after term neonatal death and nearly 7% after term small for gestational age.
Having one of the complications appeared to double the risk of a preterm birth, compared with having none of the five complications, and having two or more complications more than tripled the risk.
The researchers point out that as an observational study, they cannot establish a cause-and-effect relationship between first pregnancy complications and preterm risk in the second pregnancy, however, they add that the findings could help identify women who are at increased risk of preterm delivery, even if they previously had a full-term birth.
They conclude that serious pregnancy complications “imply an increased risk not only of recurrence of the same outcome but also of preterm birth in a subsequent pregnancy.
These findings might inform antenatal clinical care by helping to identify women at increased risk of preterm delivery.”