Fertility treatment and congenital urologic malformations: is there a solution to our correlation versus causation woes?

Fertility treatment and congenital urologic malformations: is there a solution to our correlation versus causation woes?
In their recent study, Arendt et al. (1), used data from 80,220 live born singleton boys from the Danish National Birth Cohort and the Aarhus Birth Cohort to investigate the relationship between parental subfertility and risk of cryptorchidism and hypospadias in offspring. Combining data across multiple cohorts gives their study adequate power to detect differences in risk between offspring conceived with the help of fertility treatments and those naturally conceived. Fertility treatment was self-reported and included intrauterine insemination (IUI) and in vitro fertilization (IVF).
Source: fertstert.org