Urine iodine concentrations among women in the SELFI study stratified by the estimated peritoneal retention based on delayed radiographs: at baseline, at 1, 4, 12, and 24 weeks after oil-soluble contrast medium (OSCM) hysterosalpingography (HSG), as well as the time-weighted area under the curve (TwAUC) between baseline and 24 weeks after OSCM HSG