Ultrasound can tell us a lot about a pregnancy, but it’s not always perfect. This is particularly true in the early months and, though it is rare, it is possible to have a ‘hidden twin’ who is not visible.
Nearly every pregnant woman considers the possibility that she may be carrying more than one baby. Whether it is due to suspicious signs or symptoms or just a hunch, the thought probably crosses everyone’s mind at one time.
The only way to confirm a twin or
As with most pregnancy concerns, there are some very rare exceptions. Ultrasound provides a picture of the womb, but sometimes the picture can be misleading or misinterpreted.
After twenty weeks, a second fetus should be clearly visible on ultrasound. The likelihood that there is another baby hidden in the womb is extremely minuscule. Chances are, you are not having twins if there is no evidence of multiples on ultrasound.
However, it is not unheard of, particularly when the ultrasound is performed in the first two months of pregnancy.
For example, if your first ultrasound is taken prior to eight weeks’ gestation it may clearly reveal one distinct embryo. Yet, women who have had a second ultrasound later in the first trimester or even into the second trimester have been surprised.
Their ultrasound clearly revealed two heads, four arms, and four legs. Did another baby materialize along the way? No, not at all.
Instead, the two-dimensional perspective of the first scan only caught a glimpse of one embryo. The other was shadowed — positioned directly behind the other — and not visible from the view of the ultrasound tool. It is a similar effect to what we see during an eclipse.
In many cases, there is a good reason for the hidden twin. It happens more often because the babies are monochorionic, or contained in a single chorion (sac). This forces the two fetuses to be positioned so closely together that their shadowed position could not be detected in a quick scan.