Below is a series of excellent questions and my responses related to first trimester screening from a woman who has an IVF pregnany and twins...
• At Fri Jun 27, 06:53:00 AM 2008, Anonymous said…
Hi: How reliable is first trimester screening (FTS) in twins pregnancy? I was told it is not and some said it is. We are trying to make a decision if we will pursue chorionic villus sampling (CVS). I am 36 and I would be 1 month away from 37 when it is my due date. I am now 11 weeks almost 12. I did the FTS and the ultrasound looks good. The genetic counselor said the blood test will not be as accurate as in singleton pregnancy. The spaces on the necks (nuchal translucencies) on both babies are normal and look good. We conceived using IVF (1st cycle). It is unexplained infertility. I had natural pregnancy once but miscarried during 7-8 weeks (no heart beat detected). No family history of birth defect on either side. I am Asian if this matters and my husband is white (British/ French). I really appreciate your opinion. Thank you.
• Tue Jul 01, 01:05:00 PM 2008, Anonymous said… Dr. T. I left comment earlier on 6/27 about reliable in FTS in twin. I just got the test results for FTS:
IVF/ICSI cycle 36 yrs (asian) weight 165 lbs Gest Age: 11.3 wks IDDM: no DS HX: NO NT: 1.3 mm and 1.5 mm CRL: 49.3mm and 48.3 mm Nuchal Translucency: 1.08 MoM/ 1.25 Mom PAPP-A: 3.00 MoM hCG - 1.36 Mom
Down Syndrome: Screening Risk 1:660 Age Risk 1:130 Risk Cutoff: 1:50 Trisomy 18: Screening Risk - can't accurately estimated in twin Age Risk 1:470 Risk Cutoff: 1:100
We were told by the genetic counselor and another doctor who does CVS that our position is good base on the FTS result. We would do amniocentesis at 16 weeks, but if there would be an unfortunate result, would that be too late to do selective reduction which it could be 18 weeks by the time we get the result?
I would appreciate any comment based on your expertise. These tests are very confusing and driving us crazy. Thank you so much for having such an informative blog for all Moms-to-be. W.
• At Tue Jul 01, 05:51:00 PM 2008, Kenneth F. Trofatter, Jr., MD, PhD said…
To W: Those are very good first trimester results. Personally, I have found combined first trimester screening (NT measurements plus maternal serum markers) to be very helpful in twins. Below is an abstract from a recent article that gives you some idea of its value. I would suggest an MSAFP only (and perhaps another ultrasound) at 16 weeks and then a good genetic sonogram at 18-20 weeks. If all that checks out fine, you probably do not need to have any invasive procedure done and with those first screening results, we would not ordinarily recommend a CVS at all. Of course, regardless of what we suggest, the final choice is yours!
It is not too late to do selective reduction at 18 weeeks or even later, but the risks do go up with gestational age. If you have an amnio done and you are seriously considering selective reduction if one of the babies is chromosomally abnormal, consider having a FISH study done from which you can get a result back in about 72 hours. I am NOT recommending it in your case at this time, but if you elect to proceed with the amnio,that is an option to consider.
Best of luck and please let us know how things turn out. By the way, at the time of the genetic sonogram, ask your doctors to evaluate your cervical length as well! Infertility patients are notorious for having unsuspected cervical incompetence, especially with multiple gestations!
Thanks for reading and good luck to you for the rest of the pregnancy! Dr T
Chasen, et al., First-trimester risk assessment for trisomies 21 and 18 in twin pregnancy. Am J Obstet Gynecol 2007;197:374.e1-3.
OBJECTIVE: Our objective was to describe performance of first-trimester combined risk assessment in twin pregnancies. STUDY DESIGN: Twin pregnancies that underwent risk assessment in our ultrasound unit from 2003-2006 were included. Adjusted risks for trisomies 21 and 18 that were based on age, nuchal translucency (NT), and biochemistry were provided for each twin. Detection rates for Down syndrome and trisomy 18 were calculated for age/NT, and age/NT/biochemistry at a screen-positive rate of 5% of pregnancies. RESULTS: Five hundred thirty-five pregnancies were included. Median maternal age was 34 years, with 47% of women > or = 35 years old. There were 7 fetuses in 6 dichorionic pregnancies with Down syndrome and 3 fetuses in 3 pregnancies with trisomy 18. For a 5% false-positive rate, age/NT identified 83.3% of Down syndrome and 66.7% of Trisomy 18 pregnancies. Adding biochemistry resulted in 100% detection rates for both conditions. CONCLUSION: The addition of biochemistry may enhance first-trimester risk assessment in twin pregnancies. Further studies with larger numbers of affected pregnancies are needed.