Wading Through A Million Routine Tests/Genetic Screenings


Okay, maybe not a million. But the number of tests you'll be offered from now until the end of your pregnancy is enough to make any mama's head spin. These days, we can screen for chromosomal abnormalities such as Down syndrome and Edwards syndrome; we can detect genetic conditions from Tay-Sachs disease to cystic fibrosis. We've got blood tests and DNA screenings. We've got ultrasounds and placenta samples. And that's just during the first trimester.

While some of these tests are noninvasive, and frankly, necessary- your midwife, for example, needs to know your blood type, as well as establish a baseline to monitor you for conditions such as anemia, preeclampsia, and gestational diabetes- others are entirely optional. In fact, the most overwhelming part of the prenatal testing process isn't taking the tests- most don't require more than a blood draw- it's deciding whether or not you want to take them. Some mamas want to know about any potential health issues with baby right away, to prepare emotionally or to plan logistically (perhaps by lining up specialized care both during and after the birth). Others feel that testing for genetic disorders in particular would only cause anxiety and so opt to skip them. Still others want to limit the number of ultrasounds or invasive tests their baby is exposed to while in utero.

The point is: you have choices.

Keep in mind that all the tests you'll be offered can be broken down into one of two types: screening and diagnostic. Screening tests determine the likelihood that baby might have certain genetic disorders. Diagnostic tests, on the other hand, are much more definitive; they also tend to be more invasive, which is why they're often ordered only after an initial screening has indicated a potential health issue. Here's the rundown of the tests you'll be offered.


Basic Blood Work & Urine Samples:

Without question, the least invasive of all prenatal tests is the blood draw and urine screen. Your midwife will order the blood test to check your blood type and "complete blood count" (which measure your red blood cells, white blood cells, hemoglobin, hematocrit, and platelet levels). She'll screen you for a range of sexually transmitted diseases, including HIV, syphilis, chlamydia, and gonorrhea, all of which could be harmful to baby if left untreated. She'll also check you for something called Rhesus (or Rh) factor, a type of protein found in the blood.

Most people in the world have the protein; in other words, they're Rh-positive. If you are, you have nothing more to do. Rh-negative mamas, however, may require some additional treatment. Since the Rh factor is an inherited trait, it's possible that the baby you're carrying is Rh-positive (assuming his papa is too), and your blood types are incompatible. As scary as that sounds, this won't matter much during your current pregnancy; your blood and baby's blood rarely mix while he's in utero. When and if your blood does mix, however- say during birth (which is likely, especially if you need interventions)- your body will begin to produce Rh antibodies. Then, if you get pregnant with another Rh-positive baby in the future, those antibodies can cross the placenta and attack the fetal blood supply, and that can present a serious problem. Luckily, this is all treatable. Rh-negative mamas will be offered a Rhogam shot (also called Rh immunoglobulin) at 28 weeks, which prevents your body from producing those antibodies. You may also be offered a shot after a miscarriage, amniocentesis, chorionic villus sampling, or at any other point when your blood and baby's blood is likely to mix, as well as an additional shot after the birth, but only if baby is, indeed Rh-positive.

As for the urine test, your midwife will check for signs of a urinary tract infection (UTI), which are quite common during pregnancy. She'll also check for the presence of protein in your urine (a potential sign of preeclampsia), sugar ( a sign of gestational diabetes), and bacteria (a sign of Group B Strep).

Is this test right for you?


Definitely. Blood type and Rh status in particular are vital pieces of information to have, and there's virtually zero risk to you or baby. If you're Rh negative and concerned about the Rhogam shot, you can discuss the potential risks and reqards of the treatment with your midwife. A less invasive course of action, however, is to test Papa's Rh status first. If he is negative, too, you're in the clear, since it's not possible for two Rh negative people to make an Rh positive baby. You might also want to ask about fetal RHD genotype testing, a simple blood test that can reportedly determine baby's Rh status with 99% accuracy.

Give your practitioner a heads-up if you've got genital herpes. Active outbreaks just before or during labor can sometimes necessitate a Cesearan (to prevent baby from contracting the virus). Just discovered you've got HPV? Know that human papillomavirus- the most common STI, affecting around 79 million Americans- rarely has an effect of pregnancy.




Dating Ultrasound

As the name implies, the dating ultrasound- which is typically performed between 8-12 weeks can help zero in on your baby's due date. All babies of this gestational age are about the same size, so measuring crown-to-rump length- the distance from the top of his head to his bottom- can give pretty accurate data for how far along you are. The ultrasound may be performed transvaginally (by inserting a probe into the vagina) or abdominally (using the wand on your belly). You'll likely be asked to drink a certain amount of water beforehand; when baby is this small, a full bladder can push the uterus up, making it easier to see what's inside. If there's a discrepancy of more than 5 days between the due date as determined by your last menstrual period and what's indicated by the ultrasound, your provider may change your due date. 


Is this test right for you?

You may want to skip this one if you're concerned about radiation and want to limit the number of ultrasounds you receive. In fact, some providers will offer it only if mama is unsure of the date of her last menstrual period, has very irregular periods, or if the pregnancy was a total surprise, since these scenarios can make it harder to pinpoint the date of conception. One thing to keep in mind: having an early dating ultrasound may lessen the chance that you'll be unnecessarily induced if you go post-term. Got fibroids? No problem- in almost all cases, fibroids will not prevent you from having a vaginal birth.


First Trimester Screen

Sometimes called the "nuchal translucency" or "sequential one," the First Trimester Screen is actually three separate tests that, when combined, reflect the chances of having a baby with chromosomal abnormality, specifically trisomy 21 (down syndrome) and trisomy 18 (Edwards syndrome). The test is usually performed between 10-13 weeks, and includes:

Beta hCG: This is a blood test to measure hCG levels, the same hormone that was present in your urine to give you a positive pregnancy test. Very high hCG can sometimes indicate Down Syndrome.
PAPP-A: This is a blood test to measure pregnancy associated plasma protein A (or PAPP-A) levels. Very low PAPP-A levels can sometimes indicate a chromosomal abnormality.
Nuchal Translucency: Using ultrasound, a sonographer evaluates the "nuchal fold" at the base of baby's neck; large amounts of fluid at the fold can sometimes indicate a chromosomal abnormality. The sonographer can also screen for congenital heart defects. 

Is this test right for you?

For women at risk of having a baby with a chromosomal abnormality (risk factors include advanced maternal age, a family history of chromosomal abnormalities, or a previous baby with a birth defect), this test may provide reassurance that the chances of a genetic problem with this pregnancy are low. If the results are positive, on the other hand, you can decide if you want to move forward with more invasive diagnostic testing. If you'd like to minimize the number of ultrasounds you receive during pregnancy, you may want to skip this test altogether or combine this test with the dating ultrasound; your sonographer can verify your due date, as well as let you hear baby's heartbeat during the NT screening. 


Cell- Free DNA Screening:

Sometimes called the MaterniT21, Verify, or Harmony prenatal test ( or referred to by one of several other brand names), this is a blood test that can determine the risk of having a baby with a chromosomal abnormality, specifically Down syndrome, Edwards syndrome, or trisomy 13 (Patau syndrome). It's fairly new to the market and very accurate- between 91-99% of the above defects are detected: false positives are reported in less than 1% of cases. Results may be reported as positive, negative, or as a fraction indicating the risk of a particular defect, such as 1/1,000. The test also determined the sex of the baby.

Is this test right for you?

Mamas who want to know the sex of their baby used to have to wait for the "anatomy ultrasound," which is typically performed at or around 20 weeks, the halfway point of your pregnancy. Cell-free DNA screening, on the other hand, is available at much earlier. The test can be costly, and your insurance may only cover it if you have certain risk factors. The test is not approriate for women who are expecting multiples, since it can't distinguish between one baby's DNA and another's in the maternal blood stream.

Dying To Know The Sex of Your Baby?

Well, do yourself a favor and do not buy one of those sex-predictor urine tests from your local drugstore. They're expensive and notoriously inaccurate. 


Chorionic Villus Sampling (CVS)

This is a diagnostic test, not a screen; while the results are much more accurate- CVS detects virtually any chromosomal abnormality, including Down syndrome, Tay-Sachs disease, and sex chromosomal disorders such as Turner syndrome with 98% accuracy- the test is considerably more invasive and thus carries more risks. CVS is performed by inserting a small tube into your uterus through the vagina, or by inserting a needle into your uterus through the skin of your lower abdomen to obtain a very small piece of the placenta. The tissue collection may involve some discomfort but shouldn't be painful. If the tissue is collected vaginally, you may experience a small amount of bleeding afterward. The risks, although rare, include infection, rupture of the amniotic sac, limb reduction of the baby, and miscarriage (in 1% cases). If mama is Rh-negative (and her partner is Rh-positive), she'll likely be given a Rhogam shot, since it's possible that her blood and baby's blood could mix during the procedure. CVS also requires use of an ultrasound to guide the needle or tube during insertion.

Is this test right for you?

Since CVS testing is by far the most invasive of all the first trimester tests, you likely won't want to move forward until or unless you've received an abnormal result from a First Trimester Screen and/or cell-free DNA screening. Mamas who know they intend to keep the baby no matter what may choose to opt out of this kind of testing. Know that CVS testing cannot detect problems with the baby's brain or spinal cord, such as spina bifida.