With modern ultrasound technology increasingly being routinely used in obstetric patients, a condition commonly called "vanishing twin syndrome" has become more known to physicians. Here is what you need to know about this condition.

What Does An Ultrasound Scan Show?

Most obstetricians have their pregnant patients receive their first ultrasound scan, sometimes called sonogram, anywhere from 6-10 gestational weeks. An ultrasound scan uses sound waves to create an image of the embryo and its placenta as well as umbilical cord in the uterus. The ultrasound scan will also show that the embryo has not implanted in the Fallopian tubes as well as show if there are any other potential issues to be aware of, such as implanting too near the cervical opening.

Sometimes, an ultrasound scan will also show the presence of multiple embryos. Identical twins will have one placenta, whereas fraternal twins, triplets, quadruplets, and more will each have their own placenta. Each embryo will always have their own umbilical cord that anchors them to their placenta, their lifeline to nutrients.

What Is A Vanishing Twin?

Sometimes, the initial ultrasound will show the presence of two or more viable embryos. The woman is informed she is pregnant with multiple embryos, and she then adjusts psychologically to the reality of more than one offspring. Around 16-20 gestational weeks, another ultrasound scan will be done. If multiple heartbeats are not heard before this, the ultrasound may be performed sooner. The fetuses will be much more developed at this point, as will be their placentas. The obstetrician or ultrasound technician will be able to take measurements to confirm their suspected age as well as take an overall assessment of each fetus' general health. Sometimes, the sonographer will find that there is no longer an additional fetus and that one or more have vanished. It may be that only one is now viable.

Why Has It Vanished?

Most of the time, the cause is unknown. The fetus may have had chromosomal abnormalities, it may not have implanted properly, or it may be simply some other reason known only by Mother Nature.

What Are The Symptoms Of A Vanishing Twin?

If the fetus dies during the first trimester or early in the second, there are usually no complications for mother or child. This is because the placenta generally reabsorbs the embryo, as evidenced by the appearance of the placenta at birth. Later than that, however, there may be issues such as cramps and bleeding, and the pregnancy then becomes high risk and is treated accordingly.  

To learn more, talk to your OBGYN.