title: Perinatal Advantages and Disadvantages of Being Underweight before Pregnancy: A Population-Based Study.
abstract: OBJECTIVE
  To evaluate the advantages and disadvantages of being underweight before pregnancy.
  
  
  METHODS
  Cohort study of a large population-based dataset of singleton births was used to compare maternal and neonatal outcomes of pre-gravid underweight body mass index (BMI <18.5 kg/m2) women with pre-gravid normal weight controls (BMI 18.5-24.9 kg/m2).
  
  
  RESULTS
  A total of 10,995 pre-gravid underweight and 146,155 pre-gravid normal weight mothers were compared. The mean maternal age and gestational age were not different but lean mothers were significantly and more frequently primiparous, had a higher incidence of births at <36 and <32 weeks' gestation, and had a significantly higher incidence of low and very low birth weight infants. Lean mothers had a significantly lower incidence of birth weights >4,000 g, less cesarean births and a lower incidence of gestational diabetes and hypertensive disorders.
  
  
  CONCLUSIONS
  A tradeoff exists between the advantages of being lean before pregnancy in terms of less maternal morbidity in return for gaining a more advanced gestational age and higher birth weight.
authors.affiliation: Division of Obstetrics and Gynecology, Department of Perinatology, University Medical Centre, Ljubljana, Slovenia.
authors.forename: Andreja
authors.initials: A
authors.lastname: Trojner Bregar
authors.forename: Isaac
authors.initials: I
authors.lastname: Blickstein
authors.forename: Gabrijela
authors.initials: G
authors.lastname: Bržan Šimenc
authors.forename: Vid
authors.initials: V
authors.lastname: Janša
authors.forename: Ivan
authors.initials: I
authors.lastname: Verdenik
authors.forename: Miha
authors.initials: M
authors.lastname: Lučovnik
authors.forename: Nataša
authors.initials: N
authors.lastname: Tul
mesh_terms: D000328:Adult; D001724:Birth Weight; D015992:Body Mass Index; D002585:Cesarean Section / Q000706:statistics & numerical data; D015331:Cohort Studies; D016640:Diabetes, Gestational / Q000453:epidemiology; D005260:Female; D005865:Gestational Age; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D019102:Infant, Very Low Birth Weight; D008423:Maternal Age; D011247:Pregnancy; D011248:Pregnancy Complications; D011256:Pregnancy Outcome / Q000453:epidemiology*; D047928:Premature Birth / Q000453:epidemiology; D012189:Retrospective Studies; D013851:Thinness / Q000150:complications*; D055815:Young Adult
keywords: Gestational diabetes; Hypertensive disorders; Low birth weight; Preterm birth; Underweight