A healthy 35-year-old secundigravida with a history of an uncomplicated Cesarean delivery performed four years ago for fetal malpresentation at term is referred by her primary care provider to your general obstetrics clinic at 11+5 weeks’ gestation by menstrual age. The physician provided you with a sonographic dating report confirming a viable intrauterine dichorionic diamniotic twin gestation with a crown–rump length (CRL) of twin A and B at 47 mm and 44 mm, respectively. The patient does not have any obstetric complaints and has been taking routine prenatal vitamins for the past four months. Her social and family histories are unremarkable.

A 34-year-old primigravida is referred by her primary care provider to your hospital center’s high-risk obstetrics unit after sonographic imaging confirmed viable intrauterine spontaneous monochorionic diamniotic (MCDA) twins with crown–rump lengths (CRL) of 47 mm and 44 mm, consistent for 12+4 weeks’ gestation by CRL of the larger twin. Twin A’s and twin B’s nuchal translucency (NT) measurements are 1.5 mm and 1.0 mm, respectively, with normal-appearing first-trimester fetal morphologies.