Prenatal Diagnostic Testing

We wish to reassure you as much as possible during your pregnancy that your baby is free from chromosomal and developmental problems. While no system of screening is perfect, you will find the available screening tests below.

Advanced Maternal Age Screening

  • There is a long track record of reliable statistical studies that link aneuploidy (extra chromosomal patterns in a fetus) to egg aging with advancing maternal age. As eggs age, the small fibrils that pull chromosomes apart during the last cell division prior to ovulation have a higher likelihood of fracture. This leaves extra chromosome material in the egg that will be fertilized by chromosomally healthy sperm. For instance, if extra chromosomal material remains in chromosome 13, 18 or 21 (Down’s), a baby will present with aneuploidy that can go to full term delivery and need special care. Depending on your age, your statistical likelihood of having a Down’s baby is discussed with you at your first prenatal visit.

First Trimester Screening

  • Waukesha Obstetrician first trimester screening 3D Ultrasound services in our Waukesha, New Berlin, and Mukwonago officesIf you appear to be at a higher risk for Down syndrome and/or are interested in further reassurance, our perinatology service offers first trimester screening. One phase of this screen is an ultrasound to examine a layer of skin along the baby’s head, neck, and back called the “nuchal translucency”. If it measures normally as expected, aneuploidy such as Down syndrome is much less likely. If it measures higher than expected, there is a greater association with aneuploidy / Down syndrome. Normal nuchal translucency measurements excludes up to 70% of Down’s infants.
  • The other phase of a full first trimester screen involves a blood test for HCG and pregnancy associated plasma protein A (PAPP-A). Nuchal translucency thickness coupled with maternal age gives a stronger reassurance of normality. Each first trimester factor (nuchal translucency, blood studies, and statistical tables) provides insight on risk and together they give the most complete picture of risk of aneuploidy. This combination of tests excludes up to 85% of Down’s infants.

Fetal DNA prenatal testing

  • This is a non-invasive test that detects common fetal trisomies in pregnancies of 10 weeks or more based on direct analysis of DNA in the maternal blood. This blood test is based on the newest advances in non-invasive prenatal testing. It is has been shown to have detection rates up to 99% and false positive rates as low as 0.1% for trisomy 21, 18 and 13. A low risk test reduces the chance of having an affected pregnancy. If the results show high risk, you will be referred to a genetic counselor for further testing. Not everyone qualifies or is a candidate for this test and it is done at the discretion of the high risk specialists at the Perinatal Assessment Center.

Invasive Testing

  • Expert prenatal care with Waukesha ObstetriciansChorionic Villus Sampling (CVS) is the earliest direct testing and may be performed around 13 weeks gestation. This consists of a needle sample of cells drawn from the developing placenta. Within 24 hours, the most common forms of aneuploidy (Trisomy 13, 18, 21) can be assessed along with fetal sex. After a week or more of cell cultures, a broad range of chromosomal patterns associated with fetal abnormalities can be assessed.
  • Amniocentesis may be performed between 15 and 17 weeks. This procedure involves needle penetration into the amniotic sac and gathering cells that are dispersed in the amniotic fluid. The chromosomes are analyzed in the same fashion as the chorionic villus biopsy.
  • Even with the greatest care and skill, national statistics state that 1 in 200 pregnancies are disrupted and destroyed by these invasive tests. Invasive testing is very serious, is far from routine, and probably is not worth performing unless a personal or medical decision for terminating a pregnancy is contemplated.

Quad Screening

  • Woman getting an ultrasound

    This common blood screen may be drawn between 16 and 18 weeks gestation. It values multiple factors such as maternal age, maternal weight, gestational age, and four blood elements. If the value is high, neural tube defects (such as spina bifida and hydrocephaly) are suspected. A low value is somewhat suspicious for aneuploidy. If either high or low values are seen, a full ultrasound is performed as soon as possible for reassurance. Fortunately, most results that are positive are found to be falsely positive after the ultrasound examination.
  • If you have elected to have a full First Trimester Screen, one element of the Quad Screen, alpha fetoprotein (AFP), must be drawn at 16-18 weeks to rule out neural tube defects.

20 Week Fetal Survey

  • 20 week fetal ultrasound performed in office We perform a full physical examination via ultrasound at 20 weeks gestation. Among other rare anomalies, 5 to 6 characteristics of aneuploidy might be noted during this examination. Major anomalies in your baby are not frequent occurrences, but the 20 week survey is effective in detecting many of them.
  • First trimester screening and the 20 week fetal survey are not the final diagnostic modalities to detect Trisomy 13, 18 or 21. At least 30% of fetuses with Down’s and up to 10% of fetuses with Trisomy 13 and 18 will not have any identifiable abnormalities on ultrasound.
  • The 20 week ultrasound is standard and extremely important to us for a variety of reasons. Not only are malformations screened for, but placental position, length of cervix, growth of the baby, and reconfirmation of fetal due date are identified. In addition, we can often determine the fetal sex.

Final considerations: How complete do you want your screening? This depends on your need to know in order to prepare for the birth of your child. You may feel you do not need this information in advance. You may decide you would like to know if there are any problems so you can line up special care or handle insurance issues before hand. There is no right or wrong decision, only what you and your partner determine is right for you.

We hope that this discussion will help you decide on what, if any, fetal testing you wish to have done. We will happily offer our opinion on this prior to 11 weeks gestation when decisions for first trimester prenatal screening tests must be arranged.

Contact Women's Health Care Waukesha for Prenatal Diagnostic Testing during pregnancy