Impact of maternal age on obstetric and neonatal morbidity: a retrospective cohort study

Pregnancies in women over 35 years of age are becoming more frequent. The majority of studies point to an age of 35 as a provider of obstetric and neonatal complications. But several confounding factors are not taken into account and this results in contradictory results.

The objective was to quantify the strength of the association between maternal age and obstetric and neonatal morbidity. This observational study was based on systematic records of 9 years of pregnancies managed in the Obstetrics and Gynaecology Department of Antoine Béclère Hospital, Clamart, France. In all, 24,674 pregnancies were managed at Antoine Béclère Hospital between April 1, 2007 and December 31, 2015, including 23,291 singleton pregnancies. Maternal age was the age at the beginning of pregnancy, taken as a quantitative variable. The main outcome measure was a composite "unfavourable" pregnancy outcome that included miscarriage, induced abortion, in utero foetal death, stillborn or newborn infant weighing under 500 g or delivered before 24 weeks of gestational age. Obstetric and neonatal morbidity comprised hospitalisation during pregnancy for more than 1 day, pre-eclampsia, gestational diabetes requiring hospitalisation, caesarean delivery, preterm birth, small-for-gestational age, and newborn transfer to the paediatric unit or neonatal intensive care unit.

Analyses were conducted among singleton pregnancies (n = 23,291) and were adjusted for obesity, assisted reproductive technology and geographical origin of the mother. Unfavourable pregnancy outcome rate tripled with age, from 5% among women aged 25 to 34 to 16% among those over 45. Women over 40 were twice as likely to be hospitalised as those aged 25 to 34. The caesarean section rate reached more than 40% among women over 40 and more than 60% in women over 45. The rate of newborn transfer to paediatric intensive care or a neonatal intensive care unit was doubled in women over 40 and small-for-gestational age was more frequent with age, reaching 34% in women over 45.

The risk of maternal-foetal complications increases steadily with age and is particularly high after 35 years and closer monitoring appears to be necessary. These results provide additional evidence and information for public health decision-makers.