Prenatal Tests: First Trimester
Prenatal tests can offer valuable information about your health during pregnancy. They can find problems like gestational diabetes and preeclampsia (dangerously high blood pressure), which if not treated can put your baby at risk for problems like preterm birth.
Tests can also tell you things about your baby's health, like whether your child has a birth defect or a chromosomal abnormality. Of course, no test is foolproof. Results can be inaccurate, but the chances of this happening are low.
If your doctor recommends a screening or test, be sure to learn about the risks and benefits. Most parents agree that prenatal tests offer them peace of mind while helping to prepare them for their baby's arrival. But it's your choice to accept or decline a test.
Read on to learn about tests that may be available to you during your first trimester.
First-Visit Screenings & Tests
One of the goals of your first visit to the obstetrician's office is to confirm your pregnancy and determine whether you or your baby is at risk for any health problems.
The doctor will give you a full physical, which may include a weight assessment, blood pressure check, and breast and pelvic examination. If you're due for your routine cervical test (Pap smear), the doctor will perform it during the pelvic exam. This test detects changes in your cervical cells that could lead to cancer.
To do a Pap smear, the inside of your cervix (the opening to the uterus that's located at the very top of the vagina) will be swabbed with a cotton swab. This may be a little uncomfortable, but it is over quickly. In addition, during the pelvic exam your doctor will likely check for sexually transmitted diseases (STDs) like chlamydia and gonorrhea.
To confirm your pregnancy, you may have a urine pregnancy test, which checks for hCG, a hormone and pregnancy indicator. Your urine (pee) also will be tested for protein, sugar, and signs of infection.
Blood will be drawn to check for things like:
- your blood type and Rh factor. If your blood is Rh negative and your partner's is Rh positive, you may develop antibodies that prove dangerous to your fetus. This can be prevented through a course of injections given to you.
- anemia, a low red blood cell count
- hepatitis B, syphilis, and HIV
- immunity to German measles (rubella) and chickenpox (varicella)
- cystic fibrosis — health care providers now routinely offer this screening even when there's no family history of the disorder
After the first visit, you can expect to get your urine tested and your weight and blood pressure checked at every (or almost every) visit until you deliver. The reason for this is to identify conditions such as gestational diabetes and preeclampsia.
Throughout your pregnancy, you'll be offered more tests depending on your age, health, family medical history, and other factors.
First Trimester Screen for Fetal Problems
Why Is This Screening Performed?
Doctors use this to screening test to determine a woman's risk of carrying a baby with Down syndrome (trisomy 21), Edward syndrome (trisomy 18), or other chromosomal abnormalities. It can also help determine the risk for certain birth defects like heart abnormalities.
This screening test, called the "first trimester screen," is ideally done in two parts: a blood sample (often a pinprick test to draw a drop of blood) and, usually, an ultrasound screening:
- Blood sample (maternal blood screening). This test measures the levels of proteins in the blood. Having abnormal levels of the proteins PAPP-A (maternal serum pregnancy-associated plasma protein-A) and beta-hCG (maternal serum beta human chorionic gonadotrophin) can indicate a higher-than-average risk of carrying a baby who has chromosomal abnormalities.
- Ultrasound screening (nuchal translucency screening). This exam measures the space in the back of the baby's neck. Extra fluid in the back of the neck (behind the neural tube) may point to a higher risk of chromosomal abnormalities. Ultrasound screenings are not offered at every medical practice.
When a woman undergoes both the blood and ultrasound screening, her doctor usually will calculate the results together. Age is also a consideration with determining these results, since women of advanced maternal age (35 and older) are at a higher risk of having children with chromosomal abnormalities. Combining the results provides a higher level of accuracy than if the screenings were calculated on their own. When screenings are calculated together, it's called a combined first trimester screening.
Not all doctors choose to calculate a woman's risk in this way. Some wait until after a woman has had other screenings in the second trimester to determine her baby's overall risk for chromosomal abnormalities. This is called an integrated screening. Other practitioners who do not offer a first trimester ultrasound determine a woman's risk using the results of her first and second trimester blood screenings. This is called a serum integrated screening.
How your doctor chooses to calculate your results depends on your age, health risks, and what services are available at the doctor's office.
Women who are shown to be at high risk for carrying a baby with Down syndrome or another chromosomal abnormality are offered diagnostic testing, usually through chorionic villus sampling (CVS) in the first trimester or amniocentesis in the second trimester. They also may be offered a new blood screening (cell-free fetal DNA testing) that evaluates the fetal DNA in a woman's blood and can give doctors an indication about certain chromosomal abnormalities.
Those who are not shown to be high risk in the first trimester are still offered a second trimester screening. That screening, which consists of more blood tests, checks for chromosomal abnormalities and neural tube defects, and helps to confirm the findings from the first trimester screen.
Should I Have This Screening?
These screenings are considered safe, but it's your decision whether or not you get them. Some people believe that screening and/or subsequent diagnostic testing can offer a bit more peace of mind during pregnancy. The benefit of getting a screening in the first trimester is more time to plan, prepare for, or address any health problems your child may have.
But remember that this is a screening, not a definitive test — it indicates whether a woman is likely to be carrying an affected fetus. To confirm a problem, further testing must be done.
When getting any screening, it's also important to remember that there's a chance of false-positives and false-negatives. False-positive results are when women whose results show high risk for a chromosomal abnormality go on to have healthy babies. False-negatives are when women whose results show low risk go on to have a baby with Down syndrome or another chromosomal abnormality.
Talk to your doctor if you have questions about these screenings or your results.
When Should I Have This Screening?
The blood screening is usually done between 9 and 14 weeks. Women who also get an ultrasound should have it done between 11 and 14 weeks.
How Is This Screening Performed?
For the blood screening, blood is obtained from the mother through a finger prick or a regular blood draw. Results are gathered in a lab. When the ultrasound is added, a woman will lie on her back while an ultrasound probe glides across her lower belly. To construct an image of the fetus, sound waves bounce off the baby's bones and tissues.
When Are the Results Available?
Blood screening results usually are ready within a week or two. Ultrasound results can be immediate.
Why Is This Test Performed?
Ultrasounds were once used only in high-risk pregnancies but have become so common that they're often part of routine prenatal care.
During an ultrasound, sound waves are bounced off the baby's bones and tissues to construct an image showing the baby's shape and position in the uterus. Also called a sonogram, sonograph, echogram, or ultrasonogram, an ultrasound is done to:
- verify the expected date of delivery
- detect pregnancies outside the uterus
- see whether there might be more than one fetus
- determine whether the fetus is growing at a normal rate
- record fetal heartbeat or breathing movements
- check the amount of amniotic fluid in the uterus
- indicate the position of the placenta (which block the baby's way out of the uterus) in late pregnancy
- guide doctors during other tests, like amniocentesis
- find structural defects that may indicate Down syndrome, spina bifida, or anencephaly
- detect other problems such as congenital heart defects, cleft lip or palate, and gastrointestinal or kidney malformations
Should I Have This Test?
This test is considered safe. If you opt to get the first trimester screen to check for fetal health problems, an ultrasound may be offered to you. It also might be available as part of your routine prenatal care.
When Should I Have This Test?
If you're getting the first trimester screening, you'll likely get an ultrasound between 11–14 weeks. Some providers also will order an ultrasound to date the pregnancy, usually early in your first trimester.
Women with high-risk pregnancies may need to have multiple ultrasounds throughout their first trimester.
When Are Results Available?
Although the technician can see the images immediately, a full evaluation by a physician may take up to 1 week if a physician is not on site during the exam.
Depending on where you have the ultrasound done, the technician may be able to tell you that day whether everything looks OK. However, most radiology centers or health care providers prefer that technicians not comment until a specialist has taken a look — even when everything is OK.
Chorionic Villus Sampling (CVS)
Why Is This Test Performed?
Chorionic villi are tiny finger-like units in the placenta (a disk-like structure that sticks to the inner lining of the uterus and provides nutrients from the mother to the fetus through the umbilical cord). They have the same chromosomes and genetic makeup as the fetus.
During a chorionic villus sampling (CVS), some cells from the chorionic villi are removed and tested for a number of chromosomal abnormalities, like Down syndrome, Tay-Sachs disease, or Fragile X syndrome.
This screening is considered an alternative to an amniocentesis because it can be performed earlier in pregnancy, allowing more time for expectant parents to receive counseling and make decisions. Unlike amniocentesis, CVS does not provide information on neural tube defects like spina bifida. The risks of CVS are higher than with amniocentesis so the risks and benefits of the test must be weighed.
How Is This Test Performed?
This test is done in one of two ways:
- Transcervical: Using ultrasound as a guide, a thin tube is passed from the vagina into the cervix. Gentle suction removes a sample of tissue from the chorionic villi.
- Transabdominal: A needle is inserted through the abdominal wall with ultrasound guidance, and a sample of the chorionic villi is removed.
Some women find that CVS is painless. Others feel cramping, similar to period cramps, while the sample is taken. After the sample is taken, the doctor may check the fetus' heart rate. You should rest for several hours afterward.
Should I Have This Test?
Most women who are not high risk will not need this test. But your health care provider may recommend this test if you:
- are older than age 35
- have a family history of genetic disorders (or a partner who does)
- have a previous child with a genetic disorder or had a previous pregnancy with a chromosomal abnormality
- have had an earlier screening test that indicates that there may be a concern
Possible risks of this test include:
- approximately 1% risk of miscarriage (the risk is higher with the transcervical method than with the transabdominal method)
- spotting or bleeding (this is more common with the transcervical method)
- birth defects when the test is done too early in pregnancy
When Should I Have This Test?
At 10 to 12 weeks.
When Are the Results Available?
Results are usually available within a few hours to a couple of days, depending on what the test is being used to look for.
Additional Screenings for Couples at Risk
Throughout your pregnancy, your health care provider will order other tests based on, among other things, your (and your partner's) personal medical history and risk factors. If your baby is at risk for certain hereditary conditions, you will be given an appointment to speak with a genetic counselor.
Screenings or diagnostic tests offered to those at risk for certain conditions include tests for:
- thyroid disease
- hepatitis C
- blood disorders like sickle cell disease and alpha thalassemia or beta thalassemia
- spinal muscular atrophy (SMA)
- Canavan disease
- cytomegalovirus (CMV)
- Tay-Sachs disease
- Fragile X syndrome