Identical Twins - Large CRL Difference

Discussion in 'Pregnancy Help' started by ap100, Apr 26, 2016.

  1. ap100

    ap100 New Member


    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 apologies for the length of the post. I have combined two posts into one!

    My wife had an ultrasound scan yesterday and the scan revealed that we were expecting twins, which was a big surprise, and of course very exciting. 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 big cause for concern regarding viability of the pregnancy. Future wise, this could also 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.

    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.

    I know that it isn't always a good idea to read medical papers online, due to the many individual factors involved, but with that said, I did come across this medical paper today [included below], and the results of the study found that where there was a discordance above 50% [between the CRL measurement of the two twins when the ultrasound scan took place between 7.0 and 9+6 weeks], the result was 100% single fetal loss by the time of the 11-14 week scan.

    I did however take some hope from this sentence in the paper, as our twin B does have a steady heart rate of 173 bpm:

    "The risk of single fetal loss has been reported to decrease with the progressive appearance of the embryonic structures and cardiac activity",

    I have read many posts on the forum of people with a growth discordance of up to about 20%, and the result has usually been a positive one, but I haven't as yet found anyone with a 55% CRL discrepancy between their twins, identical or otherwise, at any stage in the pregnancy.

    Would anyone mind sharing the differences between their twins CRL figures from any early ultrasound scans? (8-10 weeks etc)

    I have also included a Gestational Age (weeks) * CRL Length (mm) diagram. As you can also see, our twin B is supposed to be at 9w 3d gestational age (going by date of last period), and his CRL measurement is only 11.9mm, which looking at the chart below, is well below the bottom of the range. So this, along with the very high growth discordance compared to twin A [55%] does give me some cause for concern.

    Despite all of the information I have posted, I really am hoping for the best. In a strange way, researching things online did initially seem to help somehow, but maybe only as a way of passing the time until next weeks scan date arrives. The medical paper and diagram/chart that I have posted today though do cause quite a bit of concern.

    I would really appreciate any thoughts or opinions from people, or from anyone else who has had identical twins and has gone through something similar.

    Thank you!

    Embryonic growth discordance and early fetal loss: the STORK multiple pregnancy cohort and systematic review F. D’Antonio, A. Khalil*, E. Mantovani, and B. Thilaganathan on Behalf of the Southwest Thames Obstetric Research Collaborative (STORK)†


    "Discussion: The data from this cohort confirm that, irrespective of chorionicity, a CRL discordance ≥19% detected between 7+0 and 9+6 weeks of gestation is highly predictive of single fetal loss at the 11 –14-week scan. The risk of single fetal loss at 11–14 weeks was related to the magnitude of CRL discordance at 7+0 –9+6 weeks. Discordance in the fetal size is a relatively common finding in multiple pregnancies. Although a degree of discordance in fetal growth is usually present in all twin pregnancies, inter-twin discordance in size has been associated with a multitude of adverse outcomes including stillbirth, neonatal death, preterm birth, respiratory distress and admission to neonatal intensive care unit (Miller et al., 2012). However, while fetal growth discordance in the third trimester can be used to predict an adverse outcome both in MC and DC twin pregnancies, CRL discordance at 11–14 weeks and mid-trimester size discordance have been shown to be poorly predictive of most adverse outcomes once chromosomal and structural abnormalities have been excluded (Harper et al., 2012; D’Antonio et al., 2013a,b). In contrast to findings at 11– 14 weeks and mid-gestation, the current data demonstrate that embryonic size discordance is strongly associated with early pregnancy fetal loss. The risk of single fetal loss has been reported to decrease with the progressive appearance of the embryonic structures and cardiac activity (Dickey et al., 1990; Sampson and deCrespigny, 1992; Frates et al., 1993). Studies carried out in singletons have shown that a smaller than expected CRL detected early in pregnancy is predictive of subsequent fetal loss in the first trimester (Frates et al., 1993; Mukri et al., 2008). The association between reduced fetal size and pregnancy loss relies on the fact that impaired growth could be due to chromosomal or structural abnormalities, which are commonly associated with delayed fetal growth and intrauterine death. On the other hand, growth discrepancy may reflect a state of severe and early placental dysfunction in one twin. Previous smaller studies in twins have also shown that a discrepancy in early fetal or embryonic size may be predictive of subsequent fetal loss (Dickey et al., 1992; Kol et al."

    Diagram showing crown-rump length by gestational age. The blue line is the mean and the green area delimits the 3rd versus the 97th percentile.

    [I have marked our twins, A and B on the diagram in red]

  2. ap100

    ap100 New Member

    Or for those understandably who might not want to read such a big post above... :)

    Has anyone been expecting identical twins, and had a scan at around the 9 week mark, and one twin has been about 9 days smaller than the larger twin, and also well below the bottom line of a normal growth chart, such as the charted posted above? Thanks
  3. Hsalsa

    Hsalsa New Member

    I know this is from over a year ago, but I am in exactly the same position at 14 weeks, MCDA twins, measuring at 9 days apart, and I am SO worried for my next scan. PLEASE if you see this, reply and let me know how you got on. I can't find anything on the internet. Xx
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