Research from Denmark, published on bmj.com in February, found that preterm deliveries increased by 22% from 1995 to 2004. Even among low risk women aged 20-40, there was a 51% increase in early delivery.
The study also showed that assisted conceptions, multiple pregnancies, and elective deliveries increased during this time and were associated with early birth.
Now doctors in the UK warn that, if these trends are real, the impact for society is considerable.
Preterm deliveries account for fewer than 1 in 10 births but result in 75% of neonatal deaths and most neonatal intensive care admissions, write Andrew Shennan and Susan Bewley of St Thomas' Hospital, London.
Preterm birth also has considerable impact on long term future health. For instance, 1 in 4 survivors born less than 25 weeks' gestation have severe mental or physical disability. Even beyond 32 weeks, 1 in 3 children have educational and behavioural problems by the age of 7.
Possible reasons for the findings from Denmark are numerous and difficult to explain, say the authors, but they may include extremes of maternal weight, smoking, ethnic origin, and social class. A trend towards earlier ultrasound for dating and screening might also play a role.
Untangling the underlying causative factors may be difficult, but general public health measures to do with smoking, teenage and middle age pregnancy, prevention of sexually transmitted diseases, obesity, and social inequities are a good start, they write.
Obstetricians should re-evaluate the risks and benefits of delivering babies earlier. If these findings from Denmark are true, the implications for neonatologists, health economists, teachers, parents, and children themselves are worrying, they conclude.