A retrospective study of 127 twin pregnancies has been carried out, considering the relation between maternal weight-gain and zygosity of the ovum. At 28 weeks of gestation, the maternal weight-gain distribution goes on according to a bimodal curve, the analysis of which shows that each pike corresponds to one twin-pregnancy variety. Whatever the considered term might be (28-32-36 weeks), the maternal weight-gain is higher in DZ than in MZ pregnancies, and it should be pointed out that toxemic pregnancies, in each group, have nothing to do with this difference. This maternal weight-gain difference may reflect the known quality difference between MZ and DZ ova. The data lead to set up the more general hypothesis of an ovular regulation factor of the maternal weight-gain, in addition to classic data such as the own fetal weight, its annexes, and maternal diet.