Twins are Different Sizes

Cynthia Flynn's picture


Dear Midwife,
I found out via ultrasound on October 28th that I am pregnant with identical twins (in the same sack). On 10/28, the larger twin (twin A) was measuring 5 weeks 6 days with a faint heartbeat. Twin B was smaller (I don't know how much smaller), and no heartbeat was detectable. 5 days later, on November 2, I had a follow-up ultrasound b/c of bleeding. Twin A is now measuring 7 weeks 4 days, and twin B is measuring between 5 weeks 6 days and 6 weeks 1 day. No heartbeat for twin B yet.

Is it common to get a heartbeat for 1 twin but not the other? If Twin B is 5 weeks 6 days, is it possible that the heartbeat simply was detectable? Or do I need to give up on my hopes of having twins?



It is really too soon to say one way or the other. This is one of those times when patience is all we have to offer, sorry. Worrying certainly will not help the situation. So love both your children as much as you can; we really have very little time with any of our children, and I think we should enjoy them whenever we are blessed to be able to.

-- Cynthia, CNM. PhD.


Submitted by mamatoria on

I had a similar situation with my first pregnancy. It turned out my son had an acardiac twin (TRAP sequence). You should definitely keep following up with your doctors. twin to twin transfusion syndrome is another condition that can result in twins of different sizes. I don't want you to panic-only your doctors can diagnose any condition, but TRAP is rare and it was hard for me to connect with any one else who had experienced it. Take care of yourself!