Could it be twins???

  My sister is 14 weeks pregnant and just had  a doctors apointment yesterday.  When he listened to the heartbeat, it was very, very strong as soon as he laid the "listening device" on her tummy.  He said it sounded like there was an echo and said that it could be twins.  He is not scheduling an ultrasound for a couple more weeks.  What are the first signs that it could be twins?  Yes, twins are in the family.  The last was our grandmother who was a twin.  I would appreciate being able to share any experiences of others for my sister.  Is it possible to have an echo heartbeat and NOT have twins?
  Thanks!

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It is certainly possible that your sister could have twins, but the odds are against her. Despite all the notoriety, twins (and higher order multiple gestations) are quite rare. Dizygotic (fraternal, "two-egg") twins do run in families.
Ultrasonographic evaluation will definitively tell you if twins are present. Other things such as a uterus large for dates, etc., can provide clues but all things considered, ultrasound is "where the money is".