First Trimester Screening and Twins

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

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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.

Labels: amniocentesis, chorionic villus sampling, first trimester screening, FISH

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Chromosomal Abnormalities and Multiple Gestations - 2

…After talking with one of our genetic counselors, I went back into the room (see previous post). By this time, they had both used some tissues and were ready to talk more. They agreed to see the counselor and we walked across the hall to her office. (We are blessed with great genetic counselors). Over the course of 30-40 minutes, she explained ‘nondisjunction’ as the cause of increased risk for chromosomal abnormalities with advancing age, the actual risk for aneuploidy in midtrimester at age 40 in singleton (1/75 for Down syndrome; 1/44 for all aneuploidy) and twin pregnancies (about twice these risks that one of the babies will be abnormal in twins from different eggs), the diagnostic procedures that could be done to confirm the diagnosis, the benefits of knowing if the baby has a chromosomal abnormality with regard to decision-making during and after the pregnancy, and specific information with regard to the presumptive diagnosis of trisomy 18.

The patient was then asked if she wanted an amniocentesis and both she and her husband agreed that, based on what we had told them, they needed to know if the baby had a chromosomal problem, even though “we only want the procedure done on the baby that appeared abnormal.” (I wish I could accurately portray here the skepticism that was conveyed in the way the word “appeared” was inflected, but never being one to take away all hope, I just let it slide). I told them that under the circumstances, that was a very reasonable request. The normal ‘growth and appearance’ of the other baby probably reduced her risk for a chromosomal abnormality by as much as 90%. The procedure was then explained to them, including the small risks, and a consent was signed. As I always do under these circumstances, I made it quite clear that if the baby was lost following the amniocentesis, it would be much more likely due to the condition of the baby rather than to the procedure itself. She nodded that she understood. When asked if they had any questions, the only query was the inevitable, “I heard these things are awful…does it really hurt.” Welcoming the query, I gave her my patented reply that “it is going to be the most painful thing you have ever been through in your entire life and the large nurses in the room are here to hold you on the table.” She smiled and we did the procedure without any complications.

The amniotic fluid was sent for fetal karyotype studies by both fluorescent in situ hybridization (FISH) and routine culturing techniques. She was offered the FISH and told that a ‘presumptive diagnosis’ could be back within 48-72 hours and the routine culturing studies (results available in 10-14 days) could be used to confirm the FISH results and/or identify other chromosomal abnormalities not detected by the FISH assays; and, she readily accepted this approach. We would notify her directly as soon as any results were back and arrange for her to return to discuss the findings and options for follow-up depending on the diagnosis and her own needs.

A few days later, unfortunately, but as expected, the baby’s karyotype by FISH came back as 47XY,+18 (trisomy 18). When she was called, her immediate response was, “Some friends told me the FISH has lots of false-positives, so the baby could still be all right, right? Don’t we have to wait for the final results of the cultures?” Again, not to mince words, I told her that it was very unlikely the cultures would change the FISH results. In fact in 20 years, I have not seen a single FISH diagnosis of aneuploidy be overturned by the culture technique (although I have seen ‘negative’ FISH studies in circumstances where the final results demonstrated a chromosomal abnormality not included in the FISH profile). The silence that followed was deafening, and the crying that followed that was heartbreaking, but when she finally asked between tears, “Where do we go from here?,” I knew we were going to be alright. “Why don’t you come back to talk with us when you are ready; we’ll work you in on a moment’s notice if necessary…”

Labels: amniocentesis, aneuploidy, chromosomal abnormalities, FISH, trisomy 18, twins

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