title: Exercise in pregnancy: an association with placental weight?
abstract: BACKGROUND
  Women with high levels of physical exercise have an increased demand for oxygen and nutrients. Thus, in pregnancies of women with high levels of exercise, it is conceivable that the supply of oxygen and nutrients to the placenta is suboptimal, and growth could be impaired.
  
  
  OBJECTIVE
  The objective was to study the association of frequency of exercise during pregnancy with placental weight and placental to birthweight ratio.
  
  
  METHODS
  This was a prospective study of 80,515 singleton pregnancies in the Norwegian Mother and Child Cohort Study. Frequency of exercise was self-reported by a questionnaire at pregnancy weeks 17 and 30. Information on placental weight and birthweight was obtained by linkage to the Medical Birth Registry of Norway.
  
  
  RESULTS
  Placental weight decreased with increasing frequency of exercise (tests for trend, P < .001). For nonexercisers in pregnancy week 17, the crude mean placental weight was 686.1 g compared with 667.3 g in women exercising ≥6 times weekly (difference, 18.8 g; 95% confidence interval, 12.0-25.5). Likewise, in nonexercisers in pregnancy week 30, crude mean placental weight was 684.9 g compared with 661.6 g in women exercising ≥6 times weekly (difference, 23.3 g; 95% confidence interval, 14.9-31.6). The largest difference in crude mean placental weight was seen between nonexercisers at both time points and women exercising ≥6 times weekly at both time points (difference, 31.7 g; 95% confidence interval, 19.2-44.2). Frequency of exercise was not associated with placental to birthweight ratio.
  
  
  CONCLUSIONS
  We found decreasing placental weight with increasing frequency of exercise in pregnancy. The difference in placental weight between nonexercisers and women with exercising ≥6 times weekly was small and may have no clinical implications.
authors: Department of Obstetrics and Gynecology, Akershus University Hospital, Lørenskog, Norway.
authors: Gunvor
authors: G
authors: Hilde
authors: Department of Obstetrics and Gynecology, Akershus University Hospital, Lørenskog, Norway; Institute of Clinical Medicine, University of Oslo, Oslo, Norway.
authors: Anne
authors: A
authors: Eskild
authors: Norwegian National Advisory Unit on Women's Health, Oslo University Hospital, Rikshospitalet, Oslo, Norway; Domain for Mental and Physical Health, Norwegian Institute of Public Health, Oslo, Norway.
authors: Katrine Mari
authors: KM
authors: Owe
authors: Department of Sports Medicine, Norwegian School of Sport Sciences, Oslo, Norway.
authors: Kari
authors: K
authors: Bø
authors: Domain for Mental and Physical Health, Norwegian Institute of Public Health, Oslo, Norway; Health Services Research Unit, Akershus University Hospital, Lørenskog, Norway. Electronic address: Elisabeth.Krefting.Bjelland@ahus.no.
authors: Elisabeth K
authors: EK
authors: Bjelland
mesh_terms: D000328:Adult; D001724:Birth Weight; D015444:Exercise; D005260:Female; D006801:Humans; D009664:Norway; D009929:Organ Size; D010920:Placenta / Q000033:anatomy & histology*; D011247:Pregnancy; D011446:Prospective Studies; D011795:Surveys and Questionnaires
keywords: Norwegian Mother and Child Cohort Study; birthweight; exercise; placental weight; pregnancy