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Of Scans & Screens: The Various Types of Prenatal Screening Tests During Pregnancy

Prenatal screening tests can be a valuable keyhole to your unborn baby’s health. This guide gives you all the details.

Prenatal screening tests can offer priceless clues about your baby during your pregnancy, especially with regard to chromosomal anomalies and birth defects. Most screening tests are performed during the first and second trimesters. The important thing to remember is that screening tests are exactly what they say they are – tests for screening. They only offer you a risk ratio of possible conditions and are not diagnostic tests that can tell you for sure if your baby has a particular condition. If your baby is classified as high-risk, you may be offered follow-up diagnostic tests.

First Trimester Screening Tests

Early Pregnancy Scan

  • Gestational Age: 6 to 8 weeks
  • Type: Screening

An early pregnancy scan also called viability or dating scan is usually offered around 8 weeks of gestation and may be offered earlier if you have had complications in prior pregnancies or are experiencing spotting or bleeding. This scan provides reassurance by establishing the viability of the pregnancy through the heartbeat. It also calculates the gestation of the pregnancy and determines whether you’re carrying a singleton or multiples.

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Nuchal Translucency Scan

  • Gestational Age: 11 to 13 weeks
  • Type: Screening

The nuchal translucency ultrasound is usually performed between the 11th and 13th weeks of pregnancy. The scan is generally performed transabdominally but may be done transvaginally if your doctor deems it necessary. The scan is conducted to establish pregnancy dating, check for multiple gestations and calculate an individualised risk score for chromosomal abnormalities.

This risk score is assigned based on a variety of factors including age, fetal heartbeat, nuchal translucency thickness, fetal nasal bone structure, blood flow through the fetal heart and the ductus venosus. Couples given a high-risk score may be recommended further testing (either invasive or non-invasive) to seek a definitive diagnosis.

Do you want to know the  "Estimated date of when your baby is due?"  Check out Cloudnine's Pregnancy Due Date Calculator now!

Early Blood Tests

  • Gestational Age: 11 to 13 weeks
  • Type: Screening

The sequential integrated screening test is an effective yardstick of the risk of a chromosomal abnormality. They are used to measure the levels of pregnancy-associated plasma protein-A and human chorionic gonadotropin in maternal blood. Skewed levels of either could point to high risk. These blood tests are used in conjunction with the nuchal translucency measurement to determine overall risk.

Chorionic Villus Sampling

  • Gestational Age: 11 to 13 weeks
  • Type: Diagnostic

Chorionic villus sampling (CVS) is an invasive diagnostic procedure recommended to couples with a high risk of fetal chromosomal abnormalities. The procedure involves the extraction of a small sample of placental tissue, through a fine needle inserted into the expectant mother's abdomen. CVS can offer a conclusive diagnosis of chromosomal abnormalities and other heritable conditions.

However, it carries a miscarriage risk of 1-3%. If CVS is proposed to you, you and your partner will be counselled on the benefits and risks of the procedure, to aid you in making your decision.

Non-Invasive Prenatal Testing

  • Gestational Age: 10 weeks onward
  • Type: Advanced screening

An alternative to invasive testing is non-invasive prenatal testing (NIPT). The NIPT is a blood test that detects Down’s syndrome and other chromosomal abnormalities with remarkable precision. The test provides an accuracy rate of 98-99% for the three most common trisomies and is a useful screening option if you prefer not to risk miscarriage through invasive testing.

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To know more: About Your First Trimester

Second Trimester Screening Tests  

Fetal Anomaly Scan

  • Gestational Age: 18 to 22 weeks
  • Type: Screening

The fetal anomaly scan is an ultrasound procedure that checks the detailed anatomy of a baby at the 18- to 20-week mark. During the scan, your doctor will examine each part of the fetus and determine the position of the placenta, the amount of amniotic fluid, and fetal growth. You will be given a welcome glimpse of your baby’s brain, face, spine, heart, stomach, bowel, kidneys and limbs.

Fetal Echocardiography

  • Gestational Age: 18 to 24 weeks
  • Type: Screening

Fetal echocardiography is a detailed ultrasound examination of the fetal heart and arterial vessels. This scan is recommended to women with a family history of heart abnormalities, a  history of diabetes, an elevated first-trimester nuchal translucency reading, or visible fetal cardiac anomalies during the fetal anomaly scan.

Blood Tests

  • Gestational Age: 15 to 20 weeks
  • Type: Screening

If you’ve missed out on your first-trimester screening and would like to know your risk of fetal chromosomal anomalies, the quad marker screening test can help. The quad marker test is a blood test that measures four fetal proteins to determine a risk score.

However, it is considered less effective than early blood tests. Moreover, if you are subsequently diagnosed with a fetal abnormality, you may find it difficult to plan your next steps at this stage of your pregnancy.


  • Gestational Age: 16 to 20 weeks
  • Type: Diagnostic

Amniocentesis is an invasive procedure in which the fluid surrounding the fetus is extracted and sampled for chromosomal abnormalities. It may be recommended if you are considered high risk for fetal chromosomal abnormalities based on your nuchal translucency and blood test readings. Like CVS, amniocentesis presents a slight risk of miscarriage. If you do decide to opt for it, you will be counselled about the benefits and risks of the procedure to help you navigate your decision better.

Glucose Screening

  • Gestational Age: 24 to 28 weeks
  • Type: Diagnostic

A glucose screening test can determine the presence of gestational diabetes, a form of diabetes exclusive to pregnancy. Gestational diabetes is temporary and disappears soon after you’ve given birth. However, it can increase your chances of a large baby and in turn, a caesarean delivery.

Read More: Trimester- wise pregnancy tips

Third Trimester Screening Tests  

Group B Strep Screening

  • Gestational Age: 35 to 37 weeks
  • Type: Screening

Group B streptococcus (GBS) is a group of bacteria that cause infections in expectant mothers and newborns. GBS can be found in the mouth, throat, lower intestinal tract or vagina. While GBS in the vagina usually poses no harm to the mother, it can be dangerous for a newborn with an underdeveloped immune system. GBS may be screened when you’re around 35-37 weeks pregnant.

The condition can be alleviated via antibiotics to minimise your baby’s risk of contracting it during labor. Prenatal screening tests can prepare you for possible conditions in your baby. They can help you make decisions in advance, and prime you for scenarios you may not have planned for. By staying on top of your screening schedule, you can give your baby the promise of a healthy start to life.

Read More: Screening and Prenatal Diagnosis

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