twin baby ultrasound
Twin pregnancies are often diagnosed during the 12-week scan, although they can be detected as early as 6 weeks when two pregnancy sacs are usually clearly visible in the uterus.
At 12 weeks the sonographer will be able to detect whether you are carrying identical ( monochorionic) or nonidentical ( dichorionic) twins by examining the thickness of the membranes that separate the two amniotic sacs in the uterus.
If only two thin layers of amnion separate the cavities, the twins are identical. If a thicker membrane made up of two layers of amnion and two layers of chorion separates the twins, they are nonidentical.