Second Trimester Tests During Pregnancy

Here’s detailed information on the tests you’ll be offered during your second trimester of pregnancy, including which to take and which to avoid. 

Here’s detailed information on the tests you’ll be offered during your second trimester of pregnancy, including which to take and which to avoid.

Hooray! You’re in the honeymoon phase of your pregnancy now! The nausea is probably gone or merely lingering, and hopefully you’ve got some energy back too.

As you start to show this trimester, you may find yourself thinking more about your baby growing inside and wondering what decisions about testing lie ahead.

Hopefully, you feel comfortable discussing testing options with your provider (and if you’re not, you may want to find a different one!)

This article breaks down all the possible tests you’ll be faced with during the second trimester of your pregnancy.

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 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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Triple Screen/Quad Screen (15-20 weeks)

(You may also heard it be called the “sequential two” or the “second trimester screen” or “AFP plus.”)

What it is?
The triple screen and quad screen are two types of multiple marker tests that check levels of specific hormones and proteins in the mother’s bloodstream. The specific substances in mind are:

  1. Alpha-fetoprotein (AFP): protein made by your growing baby
  2. Human chorionic gonadotropin (HCG): a hormone made by the placenta (the same one that gave you those two lines on your pregnancy test!)
  3. Estriol: a hormone made by the placenta and the baby’s liver
  4. Inhibin A: another hormone made by the placenta (only for the quad screen, not the triple screen)

How is it done?
Like other forms of first trimester screening that you may have done, the triple screen and quad screen are very non-invasive and only involve obtaining a sample of blood from the mother.

From the sample of blood, levels of the hormones and proteins as listed above are determined to give you with a relative risk of having a baby with Down Syndrome, trisomy 18, neural tube defects (such as spina bifida or anencephaly), or problems with development of the abdominal wall.

Inhibin A helps to enhance the detection of Down syndrome, so the quad test may be preferred if you have a family history or are over age 35, which is when the risk of having a baby with Down syndrome drastically increases. Detection rates for Down syndrome may be even higher if the results of second trimester genetic screening are combined with first trimester screening results.

The test detects about 75% of neural tube defects and 75-90% of cases of Down syndrome. About 3-5% of women will have an abnormal result, but a much smaller percentage will actually have a baby with a problem. In other words, the test may produce a false positive.

How to prepare
You won’t have to do much to prepare for the blood draw–just show up!

Most of your preparation will be deciding whether or not you’d like to do the test and what you’ll do with the results.

  • Did you do screening in the first trimester? Depending on which screening and if results were normal, screening during the second trimester may not be a priority for you.
  • What will you do if the test says that there may be an abnormality? Will you confirm with more invasive diagnostic testing, such as an amniocentesis?
  • Will knowing that your baby has an abnormality help you with making plans for your pregnancy and/or delivery?

Amniocentesis (15-18 weeks)

What it is?
Although amniocentesis can technically be done anytime, it is usually performed around 15-18 weeks. It is a diagnostic test, which means that it provides highly accurate information about your baby’s genetics at the cost of being more invasive than a screening test.

In addition to diagnosing genetic abnormalities, amniocentesis can also diagnose other problems such as anencephaly (when the baby’s forebrain doesn’t develop properly), spina bifida, sickle cell disease, cystic fibrosis, and others.

The test detects about 99% of neural tube defects and nearly 100% of all genetic abnormalities, so it’s extremely accurate (but also invasive).

You can also use this test to find out the baby’s gender, although if that’s all you need to know there are much less invasive methods!

Amniocentesis may be done all by itself or may follow an abnormal first or second trimester genetic screening test or abnormal anatomy ultrasound.

How is it done?
Using an ultrasound, the doctor locates the placenta and fetus. Local anesthetic is applied to the area where a needle will be inserted through the abdomen into the uterus to remove a small sample (about one ounce) of the amniotic fluid surrounding the baby.

You may feel menstrual-like cramping during or after the procedure; the risk of miscarriage is less than 1%.

Other risks include injury to you or the baby, infection, or preterm labor.

How to prepare?
If you are having an amniocentesis because of an abnormal genetic screening result or a problem found on ultrasound, it may be important to you to have good emotional support during the procedure. The results will take 2-3 weeks to come back, but just having someone with you for the actual event may help to put your mind at ease.

Plan to take it easy after the amniocentesis, but you should be able to resume your normal activities the next day.

Consider what you’ll do with the results of the amniocentesis, like all other pregnancy testing.

Anatomy Ultrasound (around 18-22 weeks)

What it is?
The anatomy ultrasound is a standard of prenatal care that is offered to the vast majority of women in the United States. It’s usually done around 20 weeks, give or take, and serves to examine the baby’s full anatomy. At mid-pregnancy, pretty much all of the major organs are developed and the baby is still small enough that it is easy to see everything.

Ultrasounds earlier than 22 weeks may result in needing another ultrasound if not all of the anatomy can be visualized, and ultrasounds later on are not as accurate because it can be hard to visualize and make measurements as the baby grows. So it’s best to push off the 20 week ultrasound to the 22nd week. Most providers have no issue with this.

The anatomy ultrasound can detect both genetic abnormalities (assuming they produce abnormalities that can be visualized in the developing baby) as well as congenital abnormalities (problems with the development of the baby that are unrelated to genetics). The anatomy ultrasound also examines the location of the placenta to make sure it is not too close to or covering the cervix and measures amniotic fluid levels.

The anatomy ultrasound is also the one in which couples can find out the sex of the baby.

Here’s more information on baby ultrasounds.

How is it done?
By now, the baby is big enough that everything can be seen with an abdominal ultrasound, and there will be no need to ensure a full bladder prior to the procedure.

Many women want to bring their partner, children, or other important people in their lives to the anatomy ultrasound to take a peek at the baby, so you may want to make plans for that.

Depending on the skill of the ultrasonographer and cooperation of your little sweet pea, the anatomy scan usually takes about 30 minutes.

Some places are now offering 3D ultrasounds, which provide a clearer picture of the baby; however, there is no evidence that these ultrasounds actually detect abnormalities any better and there is no specific research about the safety of 2D versus 3D ultrasound imaging. Best to avoid!

How to prepare?
Even though the anatomy scan is a standard offering, you still get to decide if it is something you want to do. A number of studies have compared the efficacy of ultrasound in detecting abnormalities and preventing problems with the pregnancy. In all honesty, the results are pretty inconclusive.

In general, routine ultrasounds have not been found to improve pregnancy outcomes, and there are no professional organizations that recommend routine or casual ultrasound screening. So stay away from those “keepsake” ultrasound places!

If you want one ultrasound to check on the growth and development of the baby or to find out the gender, this is the one to do. If you’re concerned about the risks of ultrasound, you can try to find an experienced ultrasonographer who will be in and out quickly.

As with other pregnancy testing, you’ll have to decide how to respond if the anatomy scan picks up an abnormality with the baby. Perhaps you would rather remain in blissful ignorance and decline the ultrasound all together, or perhaps you would just like to be able to plan and prepare for a baby who may have special needs even if it doesn’t change much about the course of your pregnancy or your chosen place of delivery. It really is a personal choice.

CBC Blood Test (24-26 weeks)

What is it?
This is a standard blood test to again look at your iron levels, vitamin D status and thyroid function. These are important to be in optimal range as you continue on with your pregnancy.

How is it done?
It’s a simple blood draw.

How do I prepare?
No preparation is necessary

Glucose Screening (24-28 weeks)

(Might also be called a glucose tolerance test or GTT.)

What is it?
Glucose screening, or the “diabetes test” is a test that determines if you have gestational diabetes.

It is important to check for gestational diabetes because there can be problems for you or your baby if you have it and it is not well-controlled with diet or medications. Women who have gestational diabetes are more likely to give birth to large babies and have problems with the delivery, including shoulder dystocia (when the baby’s shoulder gets stuck) or difficulty breastfeeding. These women are also more likely to develop type II diabetes later in life.

Babies born to mothers with gestational diabetes may have problems regulating their blood sugar after birth and have an increased risk of obesity in the future.

How is it done?
Traditionally, the test has been done using a “Glucola” drink that is bright orange in color (yikes–food dyes!) and is loaded with a lot of other potentially toxic ingredients.

In reality, anything that contains 50g of sugar can be used for the test–some midwives recommend orange juice or jelly beans (the natural food dye ones!).

An hour after consuming the beverage or sugary food, your blood will be drawn to determine the glucose level. Women with gestational diabetes will have high levels of glucose in their blood. Some women will test in an intermediate range and have to repeat the test over a 3 hour period to determine whether or not they have gestational diabetes.

How to prepare?
You are not required to fast prior to the gestational diabetes screening, although some providers will tell you to do so. Fasting and then drinking a sugary beverage on an empty stomach without protein to help balance the sugar may lead to higher glucose levels in your bloodstream.

Some midwives also recommend you carb or sugar-load (I know, it sounds crazy!) for two to three days prior to the test so that your body gets used to processing sugars. This might help women who eat a very clean diet because consuming so much sugar in such a short amount of time may be very unnatural and their body may struggle to bring blood sugar levels back to normal.

You can also decline the gestational diabetes screening test if you wish. In fact, the American College of OB-GYNs (ACOG) says that women who are low risk do not need to be tested. In other words, if you meet most or all of the following criteria, your risk for gestational diabetes is extremely low:

  • < 25 years old
  • Normal body weight
  • No family history of diabetes
  • Not in a high risk racial or ethnic group
  • No history of abnormal glucose levels
  • No previous history of adverse pregnancy outcome associated with gestational diabetes

Good luck with your second trimester tests!

Wow! There’s a lot going on in that second trimester.

Pregnancy testing options can be very overwhelming, so it’s helpful to have a doctor or midwife that you know is on the same page as you. Be sure to bring your questions and concerns to their attention so that you can continue to have a healthy, low-intervention pregnancy.

Genevieve Howland

About the Author

Genevieve Howland is a childbirth educator and breastfeeding advocate. She is the bestselling author of The Mama Natural Week-by-Week Guide to Pregnancy and Childbirth and creator of the Mama Natural Birth Course. A mother of three, graduate of the University of Colorado, and YouTuber with over 85,000,000 views, she helps mothers and moms-to-be lead healthier and more natural lives.

1 Comment

  1. I am very, very surprised that you didn’t elaborate on the Glucol drink used for gestational diabetes testing. Since I’m not an expert I don’t want to elaborate too much here, but BVO is an especially important component that should be addressed. I am 14 weeks, have one more appt before they want to do my test, so I plan to discuss alternatives with my OB team.


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