title: An adaptive significance of morning sickness? Trivers-Willard and Hyperemesis Gravidarum.
abstract: Nausea during pregnancy, with or without vomiting, is a common early indication of pregnancy in humans. The severe form, Hyperemesis Gravidarum (HG), can be fatal. The aetiology of HG is unknown. We propose that HG may be a proximate mechanism for the Trivers-Willard (T-W) evolutionary hypothesis that mothers in poor condition should favor daughters. Using Swedish linked registry data, 1987-2005, we analyze all pregnancies that resulted in an HG admission and/or a live birth, 1.65 million pregnancies in all. Consistent with the T-W hypothesis, we find that: (i) HG is associated with poor maternal condition as proxied by low education; (ii) HG in the first two months of pregnancy is associated with a 7% point increase in live girl births; and (iii) HG affected pregnancies have a 34-percent average rate of inferred pregnancy loss, higher among less educated women.
authors.affiliation: Department of Economics/SIPA, Columbia University, United States.
authors.forename: Douglas
authors.initials: D
authors.lastname: Almond
authors.affiliation: Department of Economics, Columbia University, United States. Electronic address: le93@columbia.edu.
authors.forename: Lena
authors.initials: L
authors.lastname: Edlund
authors.affiliation: Imperial College, United Kingdom.
authors.forename: Michael
authors.initials: M
authors.lastname: Joffe
authors.affiliation: Department of Economics, Stockholm University, Sweden.
authors.forename: Mårten
authors.initials: M
authors.lastname: Palme
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D004522:Educational Status; D005260:Female; D006801:Humans; D006939:Hyperemesis Gravidarum / Q000453:epidemiology*; D011247:Pregnancy; D012737:Sex Factors; D012959:Socioeconomic Factors; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: Adaptive significance; Girl birth; Morning sickness; Trivers–Willard hypothesis