London, May 1 (IANS): Researchers have found that women whose first baby is born at full term, but experience complications in pregnancy, have an increased risk of preterm delivery (before 37 weeks) in their next pregnancy.

The findings, published in the journal The BMJ, suggest that term complications may share important underlying causes with preterm delivery that persist from pregnancy to pregnancy - and could, therefore, help identify women at increased risk of preterm delivery, despite having had a previous term birth.

For the results, researchers based in Norway and in the US set out to explore whether pregnancy complications or poor outcomes after a first term delivery might increase the risk of preterm delivery in the next pregnancy.

Their findings are based on data from Norway's Medical Birth Registry linking first and second pregnancies for 302,192 women between 1999 and 2015.Term complications included pre-eclampsia (abnormally high blood pressure and excess 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 researchers found that women with any of the five complications at term were at substantially increased risk of preterm delivery in their next pregnancy. The conclusion did not change after taking account of potentially influential factors, such as mother's age, pre-pregnancy weight, education level and smoking status.

Compared with having none of the five complications in the first pregnancy, having any one of the complications led to a doubling of preterm risk while having any two or more complications more than tripled the risk, the study said.

According to the researchers, the absolute risks for preterm delivery in the second pregnancy was three per cent with none of the five-term complications, six per cent after term pre-eclampsia, seven per cent after term placental abruption, 13 per cent after term stillbirth, 10 per cent after term neonatal death and nearly seven after term small for gestational age.

This is an observational study, so can't establish cause, and the researchers point to some limitations that may have affected the accuracy of their findings, they said.However, the results are based on high-quality population-based birth data, and were largely unchanged after a range of further analyses, suggesting that they withstand scrutiny.