title: Is maternal underweight really a risk factor for adverse pregnancy outcome? A population-based study in London.
abstract: OBJECTIVE
  To determine the maternal and fetal risk of adverse outcome during pregnancy in relation to low maternal body mass index in an unselected population.
  
  
  METHODS
  Retrospective analysis.
  
  
  METHODS
  Information for the years between 1988 and 1997 was extracted from a validated maternity database, including all but one of the maternity units in the North West Thames Region; 215,105 completed singleton pregnancies were studied. Comparison of pregnancy outcome was made on the basis of maternal body mass index at booking. There were 176,923 with a normal weight body mass index ( = 20 < 25). There were 38,182 with an underweight body mass index (< 20). Comparisons included antenatal complications (e.g. gestational diabetes, pre-eclampsia); intervention in labour, maternal morbidities (e.g. infection, postpartum haemorrhage, pulmonary thromboembolism); and neonatal outcome (admitted to special care baby unit at 24 hour of age, gestation at delivery, birthweight, stillbirth). Data are presented as percentages of outcomes in the normal and underweight groups with adjusted odds ratios and confidence intervals according to body mass index group.
  
  
  RESULTS
  In the underweight group only antenatal anaemia, preterm delivery and birthweight below the 5th centile were more frequent than in women of normal body mass index. The prevalence of certain complications, including development of gestational diabetes mellitus, pre-eclampsia, obstetric intervention and postpartum haemorrhage, were significantly lower in those with low body mass index.
  
  
  CONCLUSIONS
  Low maternal body mass index is associated with increased prevalence of some pregnancy complications, notably preterm delivery and low birthweight, but overall the outcome is favourable and several adverse outcomes are less common in this group of women.
authors.affiliation: Department of Obstetrics and Gynaecology, Imperial College School of Medicine, St Mary's Hospital, Paddington, London, UK.
authors.forename: N J
authors.initials: NJ
authors.lastname: Sebire
authors.forename: M
authors.initials: M
authors.lastname: Jolly
authors.forename: J
authors.initials: J
authors.lastname: Harris
authors.forename: L
authors.initials: L
authors.lastname: Regan
authors.forename: S
authors.initials: S
authors.lastname: Robinson
mesh_terms: D015992:Body Mass Index; D001835:Body Weight / Q000502:physiology*; D005260:Female; D006801:Humans; D008131:London / Q000453:epidemiology; D007752:Obstetric Labor, Premature / Q000209:etiology; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology / Q000209:etiology*; D011256:Pregnancy Outcome / Q000453:epidemiology; D012189:Retrospective Studies; D012307:Risk Factors