A pregnant Caucasian woman is indoors in a medical clinic. She is lying down while having an ultraso...
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Apparently Twins Can Hide In Ultrasounds

Here’s when you’ll know for sure if you’re having twins.

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When my mom and dad found out my mom was pregnant, they were both in shock, as it was not a planned pregnancy. In fact, my mom was at her gynecologist's office with my dad to ask about updating her birth control. However, nothing prepared them for the shock when Dr. Chalker said at her follow-up appointment that not only was my mom definitely pregnant, but there were two heartbeats. My dad fainted right on the floor. Clearly, my twin and I were not hiding, but can twins hide in ultrasounds? Is there any room for shock further down the road in your pregnancy?

How do you know if you have a hidden twin in an ultrasound?

While having a hidden twin on an ultrasound is pretty uncommon, it can happen, says Idries Abdur-Rahman, an OB-GYN. A twin hiding in an ultrasound is more common with an ultrasound done early in pregnancy, because of the baby’s — or babies’ — size.

Is there any way for you to know for sure you’re carrying twins, even before the ultrasound? Abdur-Rahman says not quite. “There really is no fool proof way to diagnose a twin pregnancy prior to having an ultrasound, though there are some potential clues like a higher than normal beta hCG (pregnancy hormone) levels.”

When do you find out if you’re having twins?

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“You can usually see a baby in the uterus on an ultrasound at about six weeks gestation,” explains Abdur-Rahman, “so this is the earliest that you could theoretically diagnose a twin pregnancy.”

It depends on the type of pregnancy you’re having as well. “Hidden twins are common in mono-amniotic pregnancies, which are pregnancies in which the babies are located in the same amniotic sac. A second twin that is hidden on an early ultrasound will likely be discovered later in pregnancy during the 20-week anatomy ultrasound,” he says.

By the 20-week ultrasound, you can mostly rest assured that any hidden twin will be found. they’ll typically make an appearance. “With later ultrasounds showing only one baby, you can be 99.99999999% sure that there is only one.”

How often has Abdur-Rahman delivered a hidden twin? He says while he has never personally delivered one himself, “I did have a friend who was a hidden triplet! She was born in Poland about 50 years ago, but hey, it still happened. Most hidden twins at the time of delivery are seen in patients who had little or no prenatal care, but there have been documented cases of women who had prenatal care and still delivered a hidden twin.”

While a hidden twin can happen — especially up until the 20-week anatomy scan — you typically won't have a big surprise on delivery day. So, breathe easy. If your doctor says you're having one baby, especially by the 20-week mark, you're more than likely just having one.


Idries Abdur-Rahman, an OB-GYN at the Vista Physician Group

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