Pregnancy is most often a wonderful time filled with excitement and the anticipation of a new addition to the family. At various stages of your pregnancy—the first and the second trimesters—your doctor may recommend different tests to ensure that your baby is developing normally. One such test recommended today is prenatal screening done along with ultrasound scan to monitor and ensure normal development of the baby.

What is Prenatal Screening?

  • Prenatal screening enables early identification any possible risk of having a baby with Down syndrome and other chromosomal conditions.
  • It is always good to be informed about your baby’s health at every stage of pregnancy. This test gives you early reassurance during your pregnancy.
  • This test includes a routine blood test which is combined with an ultrasound examination to identify the risk. Maternal age also forms an important criteria.
  • Prenatal screening for chromosomal abnormalities such as Down syndrome should be carried out as early as possible – preferably in the first trimester of pregnancy.
  • The advantage of early screening is that it offers more time for counseling, consideration and action if the risk of anomaly is found to be high.

How does prenatal screening help?

Prenatal screening screens for certain conditions that occur in the chromosome of the growing fetus. Each person has 23 pairs of chromosomes or 46 in all. For each pair, you get one chromosome from your mother and one chromosome from your father. A chromosomal condition may occur due to two possible reasons:

  • Change in the number of chromosome: there is an extra or missing chromosome.
  • Change in the structure of chromosome: missing, repetition or rearrangement of pieces of chromosomes.

As a result of this chromosome difference, the intellectual and physical development of the baby can be affected. Down syndrome, also known as trisomy 21 is the most common chromosomal condition. People with Down syndrome have an extra chromosome 21.

About 1 in 150 babies is born with a chromosomal condition.

Which disorders can be screened? What are the chances of having a baby with one of the conditions?

Prenatal Screening is commonly used to screen for the following chromosomal conditions:

Down Syndrome
Edwards Syndrome
Patau Syndrome
Open Neural Tube Defects (ONTDs)

Risk assessment screening for Down syndrome and open neural tube defects (ONTDs) is now a common medical practice, as approximately 1 out of every 20 women screens positive for Down syndrome, and for women age 40-44 years, up to approximately 1 in 3 screens positive for Down syndrome.

Discuss with your physician about the various options available. Your physician would be able to recommend what is best for you. You can have prenatal screening and make a choice whether or not to continue at each step.

Testing Options

Tests for: Chromosomal abnormality

Prenatal screening is generally advised by most of the Obstetricians and Gynecologists in the first trimester of pregnancy. It involves a routine blood test done on you between 9 weeks till 13 weeks and 6 days i.e. during your first trimester of pregnancy. The blood test is followed by an ultrasound examination, between 11 weeks, 1 day and 13 weeks, 6 days of your gestational age. The ultrasound confirms your baby’s age and measures the amount of fluid behind the baby’s neck (Nuchal Translucency scan or NT scan). Results of the blood test and the ultrasound are combined to estimate the risk of Down syndrome (Trisomy 21), Edwards’ syndrome (Trisomy 18), Patau syndrome (Trisomy 13) and few structural defects.

Tests for: Risk of pre-eclampsia

Pre-eclampsia or pregnancy induced hypertension, develops after the 20th week of pregnancy and affects approximately 6-8% of pregnancies worldwide. Left untreated, the condition can lead to severe complications in both the mother and her baby. Standard prenatal care typically monitors mothers for the onset of pre-eclampsia’s symptoms but with early screening, care providers can intervene before symptoms develop and prevent or lessen the severity of the illness.

Tests for: Chromosomal abnormality, structural defects and pre-eclampsia

BE HAPPY First Trimester Pregnancy Check is an enhanced screening test performed during 1st Trimester of pregnancy to find out if your baby has any risk of having a chromosomal abnormality and any structural defects. At the same time, it also checks to see if you are at risk of having pre-eclampsia, thus ensuring your well-being and the health of your baby. It is a simple test, where your doctor will take a small amount of blood sometime between 11 weeks and 13 weeks, 6 days of pregnancy. At the same time, you may have an ultrasound and your blood pressure will be measured.

For most women, the checks will assure that mother and baby are doing well and no further action is required. For a small group of women, there will be an early warning signal that indicates that the Doctor may need to request further tests, or prescribe some medication for the remainder of the pregnancy to support mother & baby. By doing an assessment early in pregnancy, it enables a care pathway to be determined for you and your baby towards a happy outcome.

Tests for: Chromosomal abnormalities and microdeletions

Non- Invasive Prenatal Screening is performed using the DNA of the fetus that is freely circulating in the mother’s bloodstream (cfDNA). This test checks the possibility of the baby being affected with any chromosomal abnormality without any risk of harming the baby. Although cfDNA only predicts the possibility of chromosomal abnormalities, the test results are comparatively more accurate and better than the other biochemical screening tests.

Tests for: chromosomal abnormalities and structural defects

If you have missed the opportunity for first trimester screening, you should undergo second trimester screening. Although, the detection rates for Down syndrome done in second trimester is lower than first trimester (generally between 65-70%), it also checks for some structural defects like ONTDs (Open Neural Tube Defects).

Prenatal screening, however, doesn’t confirm any chromosomal conditions. Therefore, based on the results of the prenatal screening, or other factors, a physician may recommend Second-Tier Testing to confirm or rule out conditions.

These are invasive procedures that are performed on the living fetal cells obtained from amniotic fluid or the placental tissue that enables study of the number and structure of the chromosomes and hence considered to be a gold standard for ruling out any chromosomal abnormality.


Most babies with chromosomal conditions are born to couples without any risk factors. However, the risk of chromosomal condition is higher due to:

  • Advanced maternal age: A mother’s chances of giving birth to a baby with Down syndrome increase with age because older eggs have a greater risk of improper chromosome division.
  • Family history: The risk rises if you or your spouse has a close family member who was born with a chromosomal condition or has a serious health problem.
  • Prior pregnancy: Typically, a woman who has one child with Down syndrome has about a 1 in 100 chance of having another child with Down syndrome.

Although, every pregnancy carries a risk of having a baby with Down syndrome, the chance increases with the mother’s age. Older women are at a higher risk of having a baby with Down syndrome or other chromosomal conditions.

Chance of Down syndrome with varying maternal age

Mother’s Age Chance of Down syndrome
25 1 in 1,250
30 1 in 950
35 1 in 385
40 1 in 100
45 1 in 30

Statistics show that since most infants are born to women under 35 years of age, over 70% of Down syndrome babies are born to this lower age group of women.

Sometimes chromosomal conditions can cause miscarriage. This is when a baby dies in the womb before 20 weeks of pregnancy. More than half of miscarriages are caused by chromosomal conditions. These conditions also can cause stillbirth, which is when a baby dies in the womb before birth but after 20 weeks of pregnancy.

Each child born with a chromosomal condition is different. Some children with chromosomal conditions have intellectual disabilities or birth defects, or both. Some children with these conditions don’t have any serious problems. The problems depend on which chromosomes are affected and how.

Screening can be performed during the first trimester, second trimester or both trimesters of pregnancy. Your physician would recommend the best time to opt for the screening.

The choice is completely yours! Most babies are born healthy. Only 2 or 3 out of 100 babies may have a serious chromosomal condition for most of these conditions, the cause is not known. Early reassurance is considered to be the best option.

Prenatal Screening will allow you to be informed about the health of your baby, even before the birth. The information you receive will be extremely valuable in helping you plan your baby’s birth. You and your clinician will also be able to decide if you need additional testing later in your pregnancy. If you learn you will have a baby with one of these chromosomal conditions, you can proactively prepare your family for the future by making important medical and financial decisions about care.

Your screening result report would tell you if you are ‘within range’ (NOT at high risk) or ‘high risk’ of carrying a baby with Down syndrome or other chromosomal abnormalities.

A ‘Within Range’ report would mean that your baby is at a low risk for Down syndrome, trisomy 18 or trisomy 13. If you get a low risk report, your doctor would ordinarily not order further prenatal testing. Note that, a low risk does not completely eliminate the possibility of having a baby with Down syndrome or other chromosomal abnormalities.

A ‘High Risk’ report would mean your baby is at an increased risk for Down syndrome or other chromosomal abnormalities. However, It doesn’t mean that the baby is having the syndrome for which the result is high. When your physician receives this result, you and your physician may choose to consider additional diagnostic testing options like Karyotyping, FISH and BoBs using the cells obtained though procedures like Chorionic Villus Sampling (CVS) or Amniocentesis. Please remember, a screening does not confirm trisomies. Hence, a high risk report should be followed by a confirmatory diagnostic test.

No, screen negative result indicates that the chance of your baby having Down syndrome or the other syndrome screened is reduced.

Usually if you are screened negative further diagnostic is not required but we strongly recommend speaking with your doctor who can suggest for your queries.

You have to undergo a confirmatory diagnostic test like of amniocentesis or chorionic villus sampling. A diagnostic test will reveal whether the baby has Down syndrome or not. These procedures are invasive and done by ultrasound guided involving drawing amniotic fluid or placental tissue for chromosomal study. Amniocentesis is usually performed between 16 to 20 weeks, and chorionic villus sampling is usually performed before 13 weeks. They are associated with a 0.5-1.0 % risk of miscarriage.

Diagnostic tests for Down and other syndromes are invasive in nature and carry a reported 0.5-1.0% chance of miscarriage. However it is recommended that you speak with your doctor whether you opt for a diagnostic procedure to screening.

The nature of the abnormality will be provided by the doctor or the genetic counselor. You can discuss with the doctor or the genetic counselor about available support from the hospitals and other organizations.

It is not mandatory; however, it is highly advisable that you have a screening test. We strongly recommend you discuss your options with your doctor who can guide you for the screening tests.

PerkinElmer Genomics works closely with health care professionals in hospitals, obstetric centres, and practices to offer comprehensive Down syndrome screening solutions. If you have any questions or concerns about screening for Down syndrome, trisomy 13 and 18, or open neural tube defects (ONTDs), and cannot find answers to your questions on this website, please contact us today, or ask your physician about the First Trimester Screening.

Pregnant women are advised that the information provided here is of a general nature and is intended to offer a better understanding of the prenatal screening process. All medical decisions should be made in consultation with a licensed physician or other professional healthcare provider.

Women suffering from the early stages of pre-eclampsia may experience few or no symptoms. However the condition can progress quickly and if left untreated, evolve into eclampsia, a life-threatening hypertensive disorder characterized by seizures. Women with severe pre-eclampsia may experience swelling or oedema, headaches, nausea and vision changes.

Risk factors of pre-eclampsia can be detected through a screening test early in pregnancy. If the risk of pre-eclampsia is found to be high, treatment to delay or prevent the disease can be started right away.

Pre-eclampsia cannot be diagnosed before your 20th week of pregnancy and is most commonly caught when symptoms are already apparent, typically after the 32nd week of pregnancy.

Reading Materials

Prenatal Screening
First Trimester Pregnancy Check
Newborn Screening
Pre-eclampsia Screening
NIScreen (Non-Invasive Prenatal Screening)