What is First Trimester Screening?: Everything You Need to Know

The first trimester of pregnancy lasts from conception to 12 weeks. Pregnancies are classified under three trimesters, with the first trimester being an important period where the baby’s development is rapid and several important organs begin to develop. The baby’s heart begins to beat, and its brain and spinal cord are formed. While this period is very important developmentally, it is also a period that can give expectant parents and doctors essential information about the baby’s risk for genetic conditions such as Down’s Syndrome (trisomy 21) and Edward’s syndrome (trisomy 18)

First-trimester screening blood tests often involve testing for various hormone levels in the maternal blood. The sample can be useful in DNA analysis of the baby for checking any potential genetic anomalies. Since these tests can cause considerable anxiety in expectant parents, they’re optional. However, they’re quite useful in helping both doctors and parents understand the developing child’s health status. Read on to know more about 1st-trimester screening, what it entails, and why it can be useful to get a 1st-trimester screening test if you’re in the early stages of pregnancy. 

first trimester screening blood test

What is First Trimester Screening?

  • First-trimester screening involves several examinations and investigations for the expectant mother to evaluate both maternal and fetal health. 
  • By evaluating your medical and family history, the doctor will look for potential risks to your and your baby's health.
  • This is followed up with a complete physical examination that involves a detailed pelvic exam. The pelvic examinations will consist of a PAP smear to rule out any potential STDs. 
  • First trimester screening blood tests form a major portion, with maternal blood group analysis and screening for infectious diseases such as rubella, AIDS, and hepatitis B. Blood tests will also reveal any nutrition and diet shortfalls and allow the doctor to correct these discrepancies on time. 
  • Your doctor might also follow up your first-trimester screening blood tests with urine tests to check for certain hormone markers and to check for glucose in case you are at high risk for gestational diabetes. 
  • Sonography and genetic testing are carried out in the later parts of the first trimester to check for any potential fetal abnormalities via both visual and gene sequencing methods. This includes both non-invasive and invasive tests. Positive results on the non-invasive results are often followed by more specific invasive testing methods such as chorionic villus sampling and amniocentesis. 

Test Procedures in First Trimester Screening

  • First-trimester screening forms the initial part of prenatal testing that keeps a tab on maternal and fetal health parameters. 
  • While aspects such as genetic testing are optional, it often helps to get tests such as the blood panels, urine examinations, and sonograms to allow the doctor to augment your monitoring plan throughout the pregnancy. 
  • Here are the various parts of 1st-trimester screening and what they entail: 
  • Blood Tests: Blood tests are an important aspect of prenatal testing in the 1st trimester. They help doctors understand various bodily parameters by using a straightforward and non-invasive procedure. Here are the various blood tests you will be suggested to undertake during 1st-trimester testing
    • Blood group & Rh Factor Testing 
      • Testing for your blood group during the first trimester is an important step to make sure any Rh compatibility is addressed beforehand.
      • The test allows doctors to ascertain Rh compatibility with the baby.
      • Doctors can also determine the baby’s Rh type using the mother’s blood sample as the child’s genetic material can be found in the maternal blood. 
      • 80% of the world population is Rh-positive, however, if your blood is Rh-negative and the child is Rh-positive, there is an incompatibility, and your body will produce antibodies against Rh-positive blood. While this doesn’t affect the first pregnancy, it can affect future pregnancies when there’s a similar Rh incompatibility. 
      • Women that have an Rh incompatibility will be given an Rh-immune globulin shot to neutralize the antibodies at 28 weeks, and another shot post-delivery. 
      • This shot is only necessary if the child is Rh-positive and the mother is Rh-negative. It isn’t necessary if the child is Rh-negative as well. 
    • Checking for Immunizations
      • Your blood sample during the first trimester’s screening blood tests will be subjected to an analysis to test whether you’ve received vaccinations for infectious diseases such as measles, rubella, diphtheria, and tuberculosis (in case you come from an area where the disease is prevalent). 
    • STD & Infectious Disease Screening
      • Diseases such as HIV, hepatitis B, syphilis, herpes, and HPV can have an impact on the developing fetus and can spread from the mother to the child across the placental barrier. 
      • The blood sample will be screened for these diseases.
    • Complete Blood Counts & Testing for deficiencies
      • Your blood sample will also be subjected to routine tests such as complete blood counts and tests for nutritional deficiencies. 
      • Serum iron counts and vitamin tests are especially important to help expectant mothers avoid anemia and micronutrient deficiencies. 
    • Sequential-integrated & Serum-integrated screening tests
      • These tests measure the levels of pregnancy-associated plasma protein-A (PAPP-A) and the hormone human chorionic gonadotropin (HCG) 
      • These are important non-invasive 1st-trimester screening tests that can help doctors decide whether further testing to assess for genetic abnormalities is necessary. 
      • Abnormal levels of PAPP-A and HCG are associated with an increased risk of genetic abnormalities and developmental disturbances. 
      • First-trimester screening results’ normal range for PAPP-A testing are: 
        • Normal - Greater than or equal to 0.5 MoM 
        • Low - Less than 0.5 MoM 
      • Normal HCG levels in the 1st trimester include: 
        • 9th to 12th week: 25,700 to 288,00 mLU/mL
        • 13th to 16th week: 13,300 to 254,000 mLU/mL
      • If these test results are abnormal, the doctor will follow up with a sonogram and gene testing to ascertain any risk factors for genetic abnormalities. 
      • First-trimester screening blood test results for PAPP-A and HCG only indicate increased risk for potential genetic abnormalities and are not used to confirm any discrepancies. They are merely used as a tool to assess the necessity of further testing and investigations. 

what is first trimester screening

  • Urine Tests
    • Urine tests are carried out to correlate findings with blood tests and to look for potential anomalies. 
    • Urine examinations during first trimester screenings are useful in detecting urinary glucose and assessing expectant mothers’ risk for gestational diabetes (especially if they have other risk factors involved). 
    • These tests are also used in assessing HCG levels and can be used to correlate findings with levels found in the blood. 
    • Urine tests along with first-trimester screening blood tests are essential general health assessment tools to determine maternal health. 
    • Urinalysis is also useful in checking for potential urinary tract infections and risk for preeclampsia - a pregnancy complication marked by protein presence in urine due to kidney damage and high blood pressure. 
  • Sonography
    • Sonography uses sound waves bounced off of tissues to create an image of the developing fetus in the womb. 
    • Sonograms in 1st-trimester screening tests allow doctors to determine exactly how far along you are at the time of testing, the exact position and developmental stage of the fetus, and the integrity of the supporting structures around the fetus. 
    • Ultrasounds can detect discrepancies in size and position. 
    • A specialized ultrasound examination called a nuchal translucency ultrasound checks for the amount of fluid at the back of the developing child’s neck. An increased amount of fluid indicates a higher risk for the development of Down’s syndrome. 
    • While the results from the ultrasound can be correlated with the blood test results, they’re still not conclusive tests. 
    • Doctors will suggest a quad marker test that can be carried out during the 2nd trimester of pregnancy. These tests have higher accuracy rates and also detect other developmental anomalies such as neural tube defects and other potential inherited diseases.


  • 1st-trimester screening results are usually denoted as positive or negative. Positive often means the child has a higher risk of developing a condition. However, it is not a certainty that your child will develop a birth defect. It merely indicates the risk of developing a genetic anomaly is higher. 
  • While accuracy rates of first-trimester screening are substantive, about 5% of tests turn up false-positive results. 
  • Your doctor will suggest further options such as genetic screening based on the result turned up on your first-trimester screening blood test results, and sonogram reports.

1st trimester screening

Genetic Screening

  • Genetic screening is considered only when the blood test and sonography results are both indicative of an increased risk for conditions such as Down’s syndrome or Edward’s syndrome. 
  • Genetic screening follows the results of 1st-trimester screening and is used to get a better picture of the overall risk of the child developing anomalies. 
  • Your doctor might suggest any of the following three genetic screening examinations to come to a conclusive understanding of the fetus’ risk for contracting genetic defects: 
    • Prenatal Cell-free DNA Screening (cfDNA Screening): This test analyzes the DNA of the child by collecting the sample from maternal blood. It can provide a high accuracy test result when screening for Down’s syndrome, Edward’s syndrome, and trisomy 13. However, the test does not screen for neural tube defects and defects of the heart septum. It is a non-invasive screening and a positive result on the test often does not warrant further, possibly invasive examinations. DNA testing can also be used to determine the child’s gender in a noninvasive manner.
    • Chorionic Villus Sampling: This is an invasive test taken by doctors when they want to get a better understanding. The doctor will collect a small sample of the outermost layer of the embryo to analyze the risk of developing genetic diseases. Though comprehensive CVS doesn’t assess the risk for neural tube defects and other developmental anomalies, this test carries a minor risk of miscarriage. 
    • Amniocentesis:  Another invasive examination, amniocentesis involves the extraction of a small amount of amniotic fluid to examine the child’s risk for genetic disorders involving trisomies and for developmental anomalies like neural tube defects. However, amniocentesis does not assess the risk for septal wall anomalies in the heart and structural abnormalities like cleft lip and palate. Like the CVS, amniocentesis also carries a minor risk of miscarriage. 

These tests can be further supplemented by tests conducted in the 2nd trimester to get a well-rounded understanding of overall risk. Get in touch with your doctor today to know more about prenatal examinations and 1st-trimester screening tests!