The first trimester is an exciting time during pregnancy!
You’ll go see your midwife or OB-GYN for the first time. You may be able to hear baby’s heartbeat! And you may get a several tests done as well.
This article breaks out the common tests that are done in the first trimester, plus what you need to do (if anything) to prepare.
Genetic Screening
The American College of OB-GYNs (ACOG) and American College of Nurse-Midwives (ACNM) both recommend that all women and their families be offered both genetic screening and diagnostic testing during pregnancy.
However, just because testing is an option doesn’t mean it’s the right choice for everyone.
Deciding whether or not to do genetic tests during pregnancy, determining which tests to choose, and then deciding what to do with the information can be an overwhelming process–the first of many decisions you’ll have to make as parents down the road.
Screening tests vs. Diagnostic tests
First, it’s important to realize that there are two types of genetic tests that can be done during pregnancy: screening tests and diagnostic tests.
- Screening tests determine the likelihood of a pregnant woman having a baby with certain conditions–in other words, these tests can tell us if she might have a baby with a condition versus if she probably won’t.
- Diagnostic tests are more certain–they tell us for sure if a baby has a specific genetic condition.
In general, screening tests tend to be less invasive than diagnostic tests. Also keep in mind that genetic tests can only give us information about conditions that are transferred genetically–they can’t provide any information about congenital problems, which are problems that occur during the baby’s development in the womb and are unrelated to genes.
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First Trimester Screen (10-14 weeks)
(Might also be called the “nuchal translucency” or “sequential one” even though it incorporates other tests as well)
What it is?
The results of three separate tests are combined with the mother’s age to provide parents with a number that reflects the chances of having a baby with a chromosomal abnormality. These three tests include:
- beta HCG: This is a blood draw to measure HCG levels. HCG is the same hormone that was present in your urine to give you a positive pregnancy tests, but this test determines exactly how high the level is in your bloodstream. High levels of HCG may be correlated with Trisomy 21 (Down’s syndrome)
- PAPP-A: Like HCG, PAPP-A levels in the bloodstream are also related to the likelihood of having a baby with a chromosomal abnormality.
- Nuchal translucency: This portion of the test uses ultrasound to measure a fold on the baby’s neck. If the fold measures less than a certain amount, there is a higher chance that the baby has a chromosomal abnormality.
Why is it done?
First trimester screening can give early information about the risk of having a baby with an abnormal number of chromosomes. The tests specifically investigates the likelihood of trisomy 21 (Down Syndrome) and trisomy 18, both of which are the result of having an extra chromosome. This test detects approximately 8-9 of 10 babies that have Down syndrome or trisomy 18 (although Down syndrome is much more common than trisomy 18).
For women who have risk factors for having a baby with a chromosomal abnormality (the woman is over 35, either parent has a history of chromosomal abnormalities in the family, or a previous baby with a birth defect or chromosomal abnormality), this screening test may be a way to reassure them that the chances of a genetic problem with the baby are low. Or if the test comes back that the chances are high, they’ll be able to decide if they want to move forward with more invasive diagnostic testing.
It is only about 3-5% of the time that the test determines there is a moderate to high likelihood of an abnormality.
How to prepare?
Since this test is non-invasive, preparing for it is pretty easy, and the risk to you and your baby is essentially non-existent other than potential emotional sequelae. There will just be a blood draw and a 20 minute ultrasound. If you’re planning to do this screening test and want to minimize total number of ultrasounds during your pregnancy, it may be wise to defer other first trimester ultrasounds as it is possible for the ultrasonographer to verify your due date based on the size of the baby (and show you your little one’s beating heart!) while they do the nuchal translucency scan.
The hardest part of your preparation will probably involve deciding what you would do with the results. Some women would want to know as early as possible if there were a genetic problem with the baby for pregnancy planning purposes. Others want to be prepared emotionally and logistically (for choosing a hospital and provider, as an example) if problems are anticipated. And some women feel that screening tests may actually cause them more worry and they’d rather find out at birth or at a later ultrasound if there was a problem.
Dating Ultrasound (8-12 weeks)
What it is?
A dating ultrasound is an ultrasound your provider may offer during the first trimester to measure the size of the baby in order to help determine an accurate due date. These results can be more accurate than those of a pregnancy due date calculator. Since there is little variation in the size of the baby during this stage of pregnancy, measuring the crown-rump length, or the distance from the top of the baby’s head to its bottom, can provide information about how far along you are in the pregnancy.
Once you have your due date from a dating ultrasound, you can use our reverse due date calculator to discover when you most likely conceived.
Why is it done?
Some providers may offer all women an ultrasound during the first trimester to date the pregnancy and check viability (see if the baby is growing on track and the heart is beating when it is expected to beat). Other providers may only offer an ultrasound if the woman is unsure of her last menstrual period or has very irregular periods.
If there is a discrepancy of more than 5 days between the due date as determined by the last period and the due date as determined by the ultrasound, your provider may decide to change your due date.
One study has shown that women who have an ultrasound to date the pregnancy are less likely to have an induction of labor for post dates (going past their due date). Routine first trimester ultrasounds also serve to detect twins or triplets early on in the pregnancy.
How to prepare?
Depending how far along you are in your pregnancy, the ultrasound may be done transvaginally (by inserting a probe into the vagina) or abdominally (the wand on your belly). Your provide may instruct you to drink a specific amount of water an hour before the test so that you’ll have a full bladder. When the baby is small, a full bladder can push the uterus up and make it easier to visualize what is inside.
Do you have very regular periods? Are you certain of the date of conception because you were tracking ovulation or there was only one time you and your partner had sex? If so, the dating ultrasound may not be necessary for you.
But if this pregnancy was a surprise or you have very irregular periods or ovulate late in the cycle, having an early ultrasound may be better than an induction of labor that could have been prevented by pinning down a more accurate due date.
Just remember, if you consent to a dating ultrasound, you’re also consenting to the potential risks that ultrasounds carry. Here’s more information on the risks vs. rewards of baby ultrasounds.
Cell-Free DNA Screening (usually first trimester, but can be done anytime)
You may also hear it called the MaterniT21 test, Harmony prenatal test, and a few other trade names.
What it is?
The cell-free DNA screening is a test of a pregnant woman’s blood, which contains small amounts of fetal DNA, to determine the risk of having a baby with a chromosomal abnormality, specifically trisomy 21, 18, or 13, or a sex chromosome abnormality.
This test can also be an early indicator of your baby’s gender if that is a piece of information you’d like to find out.
Since it’s just a blood test, it’s pretty non-invasive to the mother and completely non-invasive to the baby. The risks associated with it are extremely low. Depending on which laboratory does the test, the results can be reported as “positive” or “negative” or as a fraction indicating the risk, such as 1/1000.
The test would not be appropriate for women who know they are expecting twins, triplets, or higher order multiples because it cannot distinguish one baby’s DNA from another’s in the maternal bloodstream.
Why is it done?
This screening test is fairly new to the market and was designed with women who have risk factors for having a baby with chromosomal abnormalities in mind.
It is highly sensitive for trisomy 13, 18, and 21 and sex chromosome abnormalities as it detects these defects 91-99% of the time and rarely (less than 1% of the time) reports a genetic abnormality when there isn’t one.
Keep in mind that while this screening test is very accurate at predicting the abnormalities mentioned above, it does not screen for or detect any other genetic abnormalities.
How to prepare?
All you have to do is show up for a blood draw for this screen. It can even be done at the same time as the rest of your first trimester blood work if you have decided at that point that you want the test.
Like any other genetic test, you’ll have to decide what you would do with the information if you got a result that suggested there was an increased risk of having a baby with a chromosomal abnormality. Would you be comfortable with more invasive diagnostic testing? You will also have to decide if screening for other chromosomal problems that are not detected by this test is important to you.
Keep in mind that since this is a fairly new test and it can be costly, your insurance may not cover it unless you are over age 35 or have specific risk factors for having a baby with a genetic problem.
Chorionic Villus Sampling (CVS) (10-12 weeks of pregnancy)
What it is?
CVS is a diagnostic test for genetic problems with the baby, not a screening test like the first trimester screen or the cell-free DNA screen. This means that while the results are much more accurate (detects abnormalities with 98% accuracy), it tends to be more invasive and thus carries more risks.
The test is done by putting a small tube into your uterus through the vagina or putting a needle into your uterus through the skin on your lower abdomen to obtain a very small piece of the placenta.
Why is it done?
CVS can be done all by itself or after an abnormal first trimester screening result. It detects hundreds of genetic abnormalities including Down syndrome, Tay-Sachs disease, cystic fibrosis and problems with the baby’s sex chromosomes. In general, it can detect pretty much any chromosomal abnormality.
What it can’t detect is problems with the baby’s brain or spinal cord such as spina bifida or anencephaly.
You might consider CVS if you have a family history of genetic abnormalities, are over 35, or had a previous child with a birth defect.
How to prepare?
The ultrasound portion of this test that is used to guide the needle or tube is painless but carries with it any potential risks related to ultrasound. The tissue collecting portion may involve a small amount of discomfort but should not be painful. If the tissue is collected vaginally, you may experience a small amount of bleeding afterward.
The risks to the procedure are rare but include bleeding, infection, miscarriage (1%), Rh incompatibility in the mother (occurs if you and baby have a different blood type), limb reduction of the baby, and rupture of your bag of waters.
If your blood type is Rh negative (e.g., A-negative), you will probably receive Rhogam to reduce the chance of mixing of blood from you and your baby, which could produce antibodies that may attack future pregnancies.
Preparation for this test also includes what was previously mentioned about deciding what you’ll do with the results. Since the test is diagnostic, it is very accurate–more accurate that a screening test. This may be helpful to you, or not!
Rh-Factor Testing / RhoGAM shot (U.S.) / Anti-D (Other parts of the world)
What it is?
If the mother is Rh-negative but the father is Rh-positive, that means that baby could be either Rh-positive or -negative. This matters, because a mismatch of Rh factor between mom and baby (i.e., mom is Rh-negative and baby is Rh-positive) MAY result in some issues down the road if sensitization occurs—i.e., the two rh factor bloods are mixed and mom starts producing antibodies to it that may affect future pregnancies.
There is a test you can request at your doctor’s office that will test your baby’s Rh factor to find out if their blood carries the Rh protein—making him or her Rh positive—or if baby lacks it, meaning he or she is Rh negative. But first, you need to know mom and dad’s blood type. If either mom or dad is Rh-negative, that means baby has a chance of being Rh-negative as well, which would eliminate the need for a RhoGAM injection altogether, as there is no chance for sensitization.
If you’re hesitant about receiving the RhoGAM shot, then finding out for sure if your baby is Rh-positive might be a good idea. As mentioned, the only situation in which you may actually need the RhoGAM shot is if mother is Rh-negative, but baby is Rh-positive. This could create a sensitizing situation in which the two bloods could mix (from an injury, a fall, and eventually childbirth), resulting in a possibly antibody reaction that may affect future pregnancies.
It is highly unlikely that a first baby with a different Rh factor would be affected—unless there was a chance for sensitization, from, for example, a previous miscarriage, abortion, or mismatched blood transfusion. If those aren’t a factor, then the first pregnancy will not be affected. It is future pregnancies that are the worry here, because if sensitization DOES occur without treatment (i.e., the RhoGAM shot), then mom may start producing antibodies that may affect a future baby that is also Rh-positive. This may come in the form of mild jaundice all the way to severe rhesus haemolytic disease, which in the worst cases can result in the death of the baby.
First trimester lab tests
What it is?
First trimester blood work includes the following:
- Complete blood count (CBC)
- Blood type & Rh status
- Hepatitis antigen
- Rapid plasma reagin (RPR)
- Rubella antibody
- HIV antibody
- GC/CT (gonorrhea & chlamydia)
- Urine culture & sensitivity
Why is it done?
- Complete blood count (CBC): checks for anemia
- Blood type & Rh status: determines blood type and whether or not a woman may need rhogam during her pregnancy (given to Rh negative women to prevent sensitization to fetal blood cells that could cause problems for future pregnancies)
- Hepatitis antigen: checks for hepatitis B
- Rapid plasma reagin (RPR): checks for syphilis
- Rubella antibody: determines if a woman has immunity to German measles/rubella
- HIV antibody: checks for HIV
- GC/CT (gonorrhea & chlamydia): checks for gonorrhea or chlamydia infection
- Urine culture & sensitivity: determines if a woman has a symptomatic or asymptomatic urinary tract infection (UTI)
How to prepare?
The blood work and urine test are very simple! All you’ll need to do is get a blood draw and give a sample of urine. This test is very non-invasive and helps to rule out any sexually transmitted infections as well as determining a baseline blood count to see if anemia develops over the course of the pregnancy.
Good luck with your first trimester tests!
I bet you didn’t realize how many choices you’d have to make in the midst of first trimester symptoms like nausea and fatigue. But understanding the tests that you’ll be offered is the very first step in advocating for you and your baby’s health.
If you have any questions about any of the tests listed above, be sure to talk to your doctor or midwife.
