 Softening of the uterine cervix occurs during pregnancy.There is a possibility that this process occurs earlier in twin versus singleton pregnancies.The softening of the cervix is reflected by the level of its elasticity which can be measured sonoelastographically. A two dimension image of the cervix is obtained in the midsagittal section and the length is noted. A 2nd sonoelastography image is obtained before pressure is applied with the transducer in the area of the internal os and a third sonoelastography image is obtained until no more shortening of the anterior-posterior diameter is observed.Elastography measurements of the internal os are performed using a color map: red soft, yellow medium soft, blue medium hard and purple hard before and after the application of strain.The change between the color maps before and after strain application in singleton pregnancies will be compared to the change in twin pregnancies of similar gestational age. 