What's a normal Heart rate for twins

My daughter just found out she's pregrant with twins, she thought she was 8 weeks which we all know isn't an excate science.  She is concerned because when they did her ultrasound today they discovered twins (indentical they are in the same sac) one's heart rate is 143 the other is about 102.  The measurements but the one with the 143 as 6wks 4days and the one with 102 at 6wks and 2days.  She's concerned that something might happen with the one whos heartrate is 102?  Does she have concern to be worried at this point?

[iamadelight2001]

I just had twins, a boy and girl.  Both of their heart rates were in the 140.  What did her dr say about the 102?

[1nana]

Fetal heart rates should be between 120 and 180.

[grandma_to_be]

There is some concern about the 102.  I've looked on the web and found a site that says the heart starts beating about 5 weeks and at first is the same as the mom's but increases about 3.3 beats  per day. At six weeks 102 to 140 is a normal range and it will continue to increase until week 12.  They are running another ultrasound in two weeks to check again.