Fraternal Twins Pregnancy
Your ultrasound technician may be able to tell whether your twin babies are fraternal or identical by looking at the placenta. If you’re having twins that are fraternal, they will have their own placentas.
Identical Twins Pregnancy
It’s harder to tell with an identical twins pregnancy, though. Some identical twin babies will have their own placentas, but some will share, depending on when the fertilized egg split. If the egg split within the first three days, the twin babies will have their own placenta and membranes. If the egg splits between the fourth and ninth days, the twins will share a placenta and a chorion (the outer membrane), but have two amnions (the inner membrane). These can be called either diamniotic or monochorionic.
If the twins split after nine days, the twins will have one amnion and one chorion, however this is rare. Even more rare is when the egg splits after 12 days – this is when the twin babies are conjoined.
When you’re around 12 weeks, an ultrasound can help determine if you’re having twins. This scan can also determine whether the babies are sharing a placenta and a membrane and if you’re at risk of twin-to-twin transfusion syndrome.