“…For example, in singleton pregnancies, risk factors for preeclampsia include nulliparity, advanced maternal age (AMA), obesity, assisted reproduction, egg donation, gestational diabetes, and black race. [5][6][7] In twin pregnancies specifically, the data regarding risk factors for preeclampsia are limited either by the use of birth certificate data, 8,9 which limit their accuracy, or the fact that certain important risk factors were excluded from the analyses, including maternal body mass index (BMI), 8,9 egg donation, [8][9][10][11] and race, [9][10][11] or the fact that regression analysis was not performed, 11 all of which limit their assessment of confounding risk factors. Additionally, the effect of multifetal pregnancy reduction or spontaneous pregnancy reduction of a higher-order multiple pregnancy to a twin pregnancy on the risk of developing preeclampsia was not studied.…”