Identical Twins Crown Rump Length Discordance

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ap100 - April 26


I hope everyone is well. So, I have just joined up today really to ask for your thoughts and opinions regarding our latest ultrasound scan. 

My wife had an ultrasound scan yesterday and the scan revealed that we were expecting twins, which was a big surprise. The scans shows one gestational sac and two embryos. The second one wasn't found for a while. 

However, there is a significant size difference between the two, with twin A measuring at 8 weeks and 5 days, and twin B at 7 weeks and 3 days. The CRL measurements being 21.4mm and 11.9mm respectively. 

This works out at about a 55% CRL measurement difference between the two babies. 

From what I have read, even a figure up of to around 15-20% would be classified as a 'significant' difference, and a huge cause for concern, and could point to possible TTTS or SIUGR, so seeing this 55% figure has me really worried. The technician doing the scan was concerned and mentioned often how much smaller twin B was compared to twin A.

I found a medical paper online which specifically correlated this % discordance in twins with the % of losing a single fetus. The study found that in all cases where the discordance was over 50% between the two twins [when scanned between 7.0 and 9+3 days], this would mean a lost single fetus by the time of the 11-14 week scan. 

Our twin A has a heart rate of 171bpm, and twin B has a heart beat of 173bpm. Hearing the two heart beats gives me hope. 

I am hoping that twin B will catch up with twin A, and that maybe as this is an early scan, there is room for that to happen, but with identical twins, sharing a placenta, don't both babies usually grow at around the same rate? 

I also wonder if it could be possible that the size measurement could have been inaccurate. 

We have another ultrasound booked for a weeks time, and I would appreciate anyone's thoughts or comments, or to hear from anyone who might have gone through a similar experience. Twin B's crown rump length is also below below the minimum range for the gestational age (9w+3). 

Many thanks



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