First Trimester Prenatal Screening and Ultrasound Exam:
While the majority of pregnant women will give birth to healthy infants, some may give birth to infants with major physical and mental disabilities. In some infants the problem is a chromosomal abnormality such as Down syndrome, Trisomy 18 or 13, where there is extra chromosomal material which leads to serious mental deficiency and birth defects. Although any woman can give birth to an infant with a chromosomal abnormality, the risk increases gradually with age. Please refer to table regarding your age related risk.
The gold standard in making the diagnosis of a chromosomal abnormality is amniocentesis or chorionic villous sampling (CVS). These procedures carry small risk of miscarriage (amniocentesis is about 1in 300 and CVS about 1in 100).
Many women ask about alternatives to amniocentesis or CVS. There is no alternative if the patient or the couple wants 100% accuracy. However, there are non-invasive alternatives referred to as Screening Tests. Available screening tests are either done in the first or the second trimester.
First Trimester: This includes a Sonogram done between 11 and 14 weeks and a blood test. The Sonogram evaluate the skin thickness of the baby’s neck known as the Nuchal Translucency (NT), and the baby’s Nasal bone (NB). The blood test measures one or two substances in your blood known as B-HCG and PAPP-A. With First trimester screening, the detection rate is 91% for Down syndrome, and 97% for Trisomy 18 and 13 with a false positive rate of 5%. This makes the first trimester screening the most accurate non-invasive test in the detection of Down syndrome, Trisomy 18 and 13.
Second Trimester: Traditionally a blood test known as triple and quadruple screen (or AFP Test), these tests detect between 65 and 80% with a false positive rate of 5%. These blood tests are done between 15 and 20 weeks and screen for Down syndrome, Trisomy 18, and Spina Bifida.
Frequently asked questions (FAQ):
1. Who should perform Nuchal translucency and first trimester screening?
The provider should be accredited by the Fetal Medicine Foundation (www.fetalmedicine.com), or the Maternal Fetal Medicine Foundation (www.mfmf.org).
The provider should have the knowledge and experience to counsel the pregnant woman and her partner about her risk, the test's pros and cons, the interpretation of the result, and available options for the couple if the result indicates an increased risk for Down syndrome, Trisomy 18 or 13. In addition the provider should be able to offer diagnostic testing such as amniocentesis and CVS when the patient desires a definitive diagnosis.
The provider should be experienced in maternal and fetal medicine. All our Doctors are credentialed by both the Fetal Medicine Foundation (England), and the Maternal-Fetal Medicine Foundation (USA) and are Board Certified in Maternal Fetal Medicine.
2. How are the results of the First Trimester screening used?
Your age related risk for Down syndrome, Trisomy 18/13 will be modified to a lower or a higher risk which then falls into one of three categories:
Low risk: The risk of having a baby with Down syndrome, Trisomy 18 or 13 is unlikely and the risks of amniocentesis and CVS are much higher than the risk of having any of these problems. Generally, no further testing is required and you may be scheduled to have the 20 weeks anomaly scan (level 2 ultrasound), and the AFP testing for Spina Bifida.
High Risk: The risk of having a baby with Down syndrome, Trisomy 18 or 13 is higher than the risks of amniocentesis or CVS. Keep in mind, however, that only amniocentesis or CVS can tell you with 100% certainty if these conditions exist or not.
Intermediate risk: The risk of having a baby with Down syndrome, Trisomy 18 or 13 is less than the risks of amniocentesis or CVS and falls in between the high and the low risk. Women with results in this category may benefit from additional testing such as the sequential screening or the second trimester genetic scan after 15 weeks. Combination of First and Second Trimester Screening improves the detection rate if the second trimester test takes into consideration the result of the first trimester test. Not doing so results in a higher false positive result and increases the need to have amniocentesis.
3. How Can I Schedule Any of these Tests?
Please call any of our offices and we will gladly schedule you for an immediate appointment. You will be seen by one of our Maternal Fetal Medicine Doctors who will counsel you in detail about your options and will perform the necessary tests.