title: Risk of Adverse Obstetric and Neonatal Outcomes by Maternal Age: Quantifying Individual and Population Level Risk Using Routine UK Maternity Data.
abstract: OBJECTIVE
  The objective of this study was to investigate whether moderately increased maternal age is associated with obstetric and neonatal outcome in a contemporary population, and to consider the possible role of co-morbidities in explaining any increased risk.
  
  
  METHODS
  Secondary analysis of routinely collected data from a large maternity unit in London, UK. Data were available on 51,225 singleton deliveries (≥22 weeks) occurring to women aged ≥20 between 2004 and 2012. Modified Poisson regression was used to estimate risk ratios for the association between maternal age and obstetric and neonatal outcome (delivery type, postpartum haemorrhage, stillbirth, low birthweight, preterm birth, small for gestational age, neonatal unit admission), using the reference group 20-24 years. Population attributable fractions were calculated to quantify the population impact.
  
  
  RESULTS
  We found an association between increasing maternal age and major postpartum haemorrhage (≥1000ml blood loss) (RR 1.36 95% CI 1.18-1.57 for age 25-29 rising to 2.41 95% CI 2.02-2.88 for age ≥40). Similar trends were observed for caesarean delivery, most notably for elective caesareans (RR 1.64 95% CI 1.36-1.96 for age 25-29 rising to 4.94 95% CI 4.09-5.96 for age ≥40). There was evidence that parity modified this association, with a higher prevalence of elective caesarean delivery in older nulliparous women. Women aged ≥35 were at increased risk of low birthweight and preterm birth. We found no evidence that the risk of stillbirth, small for gestational age, or neonatal unit admission differed by maternal age.
  
  
  CONCLUSIONS
  Our results suggest a gradual increase in the risk of caesarean delivery and postpartum haemorrhage from age 25, persisting after taking into account maternal BMI, hypertension and diabetes. The risk of low birthweight and preterm birth was elevated in women over 35. Further research is needed to understand the reasons behind the high prevalence of elective caesarean delivery in nulliparous older mothers.
authors.affiliation: Department of Non-communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom.
authors.forename: Laura
authors.identifier: http://orcid.org/0000-0002-4697-4316
authors.initials: L
authors.lastname: Oakley
authors.affiliation: King's College London School of Medicine, London, United Kingdom.
authors.forename: Nicole
authors.initials: N
authors.lastname: Penn
authors.affiliation: Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom.
authors.forename: Maria
authors.initials: M
authors.lastname: Pipi
authors.affiliation: Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom.
authors.forename: Eugene
authors.initials: E
authors.lastname: Oteng-Ntim
authors.affiliation: Department of Non-communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom.
authors.forename: Pat
authors.initials: P
authors.lastname: Doyle
mesh_terms: D000328:Adult; D002585:Cesarean Section / Q000009:adverse effects*; D036861:Delivery, Obstetric / Q000009:adverse effects*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008131:London; D008423:Maternal Age; D010298:Parity / Q000502:physiology; D006473:Postpartum Hemorrhage / Q000209:etiology*; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D047928:Premature Birth / Q000209:etiology; D012306:Risk; D050497:Stillbirth / Q000453:epidemiology; D055815:Young Adult