Logistic regression parameter estimates (± s.e.) of the effects of maternal height, height², birth weight, birth weight², parental height differences and their interactions on the probability of an emergency Caesarean section.

Height in centimeters, weight in kilograms. PHD is parental height differences ( = paternal height−maternal height). *p<0.05; **p<0.01; ***p<0.001 (significance based on Wald test statistic with df = 1). aWe also ran models which included all two-way interactions with maternal height2 and birth weight2. None of these terms were significant (all p>0.12). We always included the underlying (interaction with the) linear term when including a(n interaction with a) squared term in the model.