title: Hyperemesis gravidarum and pregnancy outcomes in the Norwegian Mother and Child Cohort - a cohort study.
abstract: BACKGROUND
  Hyperemesis gravidarum (HG) characterized by excessive nausea and vomiting in early pregnancy, is reported to be associated with increased risks for low birthweight (LBW), preterm birth (PTB), small-for-gestational-age (SGA) and perinatal death. Conflicting results in previous studies underline the necessity to study HG's potential effect on pregnancy outcomes using large cohorts with valid data on exposure and outcome measures, as well as potential confounders. This study aims to investigate associations between HG and adverse pregnancy outcomes using the Norwegian Mother and Child Cohort Study (MoBa).
  
  
  METHODS
  All singleton pregnancies in MoBa from 1998 to 2008 were included. Multivariable regression was used to estimate relative risks, approximated by odds ratios, for PTB, LBW, SGA and perinatal death. Linear regression was applied to assess differences in birthweight and gestational age for children born to women with and without HG. Potential confounders were adjusted for.
  
  
  RESULTS
  Altogether, 814 out of 71,468 women (or 1.1%) had HG. In MoBa HG was not associated with PTB, LBW or SGA. Babies born to women with HG were born on average 1 day earlier than those born to women without HG; (-0.97 day (95% confidence intervals (CI): -1.80 - -0.15). There was no difference in birthweight when maternal weight gain was adjusted for; (23.42 grams (95% CI: -56.71 - 9.86). Babies born by women with HG had lower risk for having Apgar score < 7 after 1 minute (crude odds ratio was 0.64 (95% CI: 0.43 - 0.95)). No differences between the groups for Apgar score < 7 after 5 minutes were observed. Time-point for hospitalisation slightly increased differences in gestational age according to maternal HG status.
  
  
  CONCLUSIONS
  HG was not associated with adverse pregnancy outcomes. Pregnancies complicated with HG had a slightly shorter gestational length. There was no difference in birth weight according to maternal HG-status. HG was associated with an almost 40% reduced risk for having Apgar score < 7 after 1 minute, but not after 5 minutes. The clinical importance of these statistically significant findings is, however, rather limited.
authors.affiliation: Department for Genes and Environment, Division for Epidemiology, Norwegian Institute of Public Health, Nydalen, P,O, Box 4404, Oslo 0403, Norway. ase.vigdis.vikanes@fhi.no.
authors.forename: Åse V
authors.initials: ÅV
authors.lastname: Vikanes
authors.forename: Nathalie C
authors.initials: NC
authors.lastname: Støer
authors.forename: Per
authors.initials: P
authors.lastname: Magnus
authors.forename: Andrej M
authors.initials: AM
authors.lastname: Grjibovski
mesh_terms: D000328:Adult; D001034:Apgar Score; D001724:Birth Weight; D016022:Case-Control Studies; D005260:Female; D005865:Gestational Age; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D006939:Hyperemesis Gravidarum / Q000453:epidemiology*; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D009664:Norway / Q000453:epidemiology; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D047928:Premature Birth / Q000453:epidemiology; D018570:Risk Assessment; D055815:Young Adult