Caesarean section among relatives.
BACKGROUND
Caesarean section rates are increasing. It is not clear whether a familial predisposition to caesarean section exists.


METHODS
Births registered in the Medical Birth Registry of Norway during 1967-2005 were linked to construct 440,236 grandmother-parent units and 275,001 same sex full sibling units. Log-binomial regression models were used to explore associations.


RESULTS
A mother born by caesarean section had a 55% increased risk of having her first child by caesarean section [adjusted relative risk (RR) 1.55, 95% CI 1.48-1.62]. The same was not found for fathers born by caesarean section (RR 1.02, 95% CI 0.96-1.10). A younger sister, whose older sister had her first child by caesarean section, had a 45% increased risk of having her first child by caesarean section (RR 1.45, 95% CI 1.40-1.51). If an older brother had his first child by caesarean, this did not constitute an increased risk for the younger brother's partner (RR 1.02, 95% CI 0.97-1.08). Similar associations were found in the subgroups of obstetric low risk deliveries.


CONCLUSIONS
A female-to-female familial predisposition to caesarean section was observed. It could be caused by biologic inheritance, primarily working through maternal alleles and/or environmental factors. The results imply that both mechanisms could be important.
Tollånes
Mette C
MC
Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway. mette.tollanes@isf.uib.no
Rasmussen
Svein
S
Irgens
Lorentz M
LM
D002585:Cesarean Section; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D004777:Environment; D005190:Family; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008423:Maternal Age; D009664:Norway; D016017:Odds Ratio; D011247:Pregnancy; D012306:Risk; D012737:Sex Factors