The higher risk of preterm births for women over 40 may not be completely explained by their greater use of reproductive technology or medical interventions like induced labour or planned caesarean deliveries, a Canadian study suggests.
The study confirmed that women over 40 do have the highest risk of preterm births: 7.8 % of pregnancies in this age group resulted in preterm births and 1 % ended in extremely premature deliveries. Women age 30 to 34 had the lowest risk: 5.7 % of pregnancies involved preterm deliveries and 0.6 % resulted in extremely early arrivals.
Compared with women age 30 to 34, the over-40 mothers were 14 % more likely to have a spontaneous preterm delivery and 31 % more likely to have early deliveries because of labour induction, caesarean births or other interventions. This offers fresh evidence that age is an independent risk factor for preterm births, researchers conclude in PLoS One.
“A common hypothesis is that the increased risk of preterm birth among aged mothers is largely explained by early labour induction for medical conditions,” said Dr Antonio Simone Lagana of the Filippo Del Ponte Hospital and the University of Insubria in Varese, Italy.
“However, this study found that advanced maternal age (40 years and over) was associated with an increased risk of preterm birth even after adjustment for known confounders, such as placenta previa, gestational diabetes, medical history, use of assisted reproduction technologies and occurrence of invasive procedures that are all more common in older mothers,” Lagana, who wasn’t involved in the study, said by email.
The oldest mothers in the study had a higher risk of going into early labour on their own and also of having a premature delivery induced for medical reasons. This suggests that not all of the increased risk of premature deliveries can be explained by decisions doctors make in the delivery room, said Dr Alice Goisis of the London School of Economics.
“The association cannot be entirely attributed to medical interventions alone,” Goisis, who wasn’t involved in the study, said by email.
In the weeks immediately after birth, preemies often have difficulty breathing and digesting food. They can also encounter longer-term challenges such as impaired vision, hearing and cognitive skills, as well as social and behavioural problems.
Pregnancy normally lasts about 40 weeks, and babies born after 37 weeks are considered full term. The study focused on preterm babies delivered during weeks 32 to 36 of pregnancy, as well as on extremely premature infants delivered before 32 weeks’ gestation.
The study by Dr Florent Fuchs of CHU Sainte Justine in Montreal and colleagues examined data on 184,000 births in 32 hospitals in Quebec, Canada. Fuchs didn’t respond to emails seeking comment.
Women over 40 in the study were more likely to have many risk factors for prematurity such as obesity, pregnancy-related diabetes or high blood pressure, and a complication known as placenta previa, when the placenta nourishing the baby separates from the uterine wall.
One limitation of the study is that data on weight was missing for 28% of participants. Researchers also lacked data on several factors that can influence the chances of a preterm birth including socioeconomic status.
Even so, the results add to the evidence that advanced maternal age can make a preterm birth more likely, said Dr Ali Khashan of the School of Public Health and INFANT Center at University College Cork in Ireland.
But all women, including older women, can take steps to reduce their odds of a preterm birth, Khashan, who wasn’t involved in the study.
“Women who are planning pregnancy, especially after age 40, should optimise their health pre-pregnancy, maintain a healthy weight, and engage with health services early in pregnancy,” Khashan advised.