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Nuchal Translucency Screening

At 12 weeks, 6 days pregnant with twins, this morning we had our first prenatal screening test – the Nuchal Translucency (NT) screening ultrasound. The NT is performed between 11 and 14 weeks (gestational age), and it is an ultrasound to measure the amount of fluid accumulation at the back of the neck, just under the skin. A more than normal amount of fluid is associated with a higher risk of Down Syndrome, Trisomy 18, or certain heart abnormalities. It must be performed before 14 weeks because after that the fetus develops a lymphatic system, which would drain any excess fluid from the area, hence making the test unreliable.

Luckily both of our babies had normal NT thickness. Baby A had a thickness of 1.43mm, and Baby B had a thickness of 1.55mm, both well within normal (should be less than 2.5mm). These results were combined with results from the first prenatal bloodwork screening that measured PAPP-A (pregnancy-associated plasma protein A) and hCG (human chorionic gonadotropin) levels to give us a “risk assessment” for Down Syndrome and Trisomy 18. In addition to NT results, PAPP-A, and hCG levels, they also factor in the number of fetuses, maternal age, weight, race, diabetic status, and smoking status to calculate the risk of having a baby with Down Syndrome or Trisomy 18.

Our estimated First Trimester Combined Screening risks were calculated as:

  • Down Syndrome Risk = 1 in 2,400, which is lower than the cutoff of 1 in 100
  • Trisomy 18 Risk = 1 in 35,000, which is lower than the cutoff of 1 in 50

This was also a big day for us because it was the first ultrasound after hitting the 12-week mark. This was the first ultrasound they did with the ultrasound wand on top of the belly (instead of inside the vagina)! We knew that up until 12 weeks, there was a possibility of one twin dying and being reabsorbed. Now that we’ve seen two heartbeats on this morning’s ultrasound, the chance of something bad happening to one is very slim. Sure, it’s still possible, but it is very unlikely now. They were also able to confirm that they are diamniotic and dichorionic (they each have their own amniotic sac and chorion), which is the least risky twin pregnancy possible. What a relief!

Today’s Stats
Baby A: CRL 68.5mm, heart rate 144 beats/min
Baby B: CRL 61.9mm, heart rate 158 beats/min

Baby A’s crown-rump length (CRL) correlates to 13 weeks, 1 day while Baby B’s CRL correlates to 12 weeks, 5 days. Considering we are at 12 weeks, 6 days from the date of insemination, both measure normally. The ultrasonographer said that one will likely always be slightly larger than the other, but their growth is considered normal as long as they both measure within two weeks of accuracy for the estimated delivery date (EDD, May 27, 2011). Both of the heart rates were also normal for their gestational age.

And the best part – photos!

Baby A:

Baby B:

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