Prenatal Screening

Prenatal Screening

Definitive prenatal diagnosis of chromosome abnormalities through the analysis of amniocytes or chorionic villus samples (CVS) is an accepted part of prenatal care. However, amniocentesis and CVS procedures carry some degree of risk for miscarriage or other pregnancy complications (Tabor and Alfirevic, 2010). Therefore, in most developed countries it is routine practice to provide a woman’s personal risk for fetal aneuploidy (screening) and to offer definitive diagnosis through amniocentesis or CVS if the risk is high.

Prenatal Screening provides an opportunity to re-assure most women that their fetus is unlikely to be affected by a chromosomal disorder (and thereby reduce the number of unnecessary invasive procedures performed) while identifying those women at highest risk for an affected pregnancy. Potential follow up options for women who are identified as being at high risk based on any of these screening options can include further counseling, additional testing and appropriate follow-up obstetriccare.

Because Down syndrome (trisomy 21) is the most common significant aneuploidy, prenatal screening has emphasized the detection of this disorder. However, it is recognized that many of the screening tests have a variable potential to detect other aneuploidies, some other genetic disorders, specific fetal anatomic abnormalities, and pregnancy complications such as preeclampsia


Prenatal screenings are advanced genetic tests conducted on normal blood samples that help identify women whose pregnancies have a high risk of carrying a fetus with a genetic abnormality. Screening is the first step & this identification helps determine the further course of action for doctors as well as the prospective parents.  Statistically speaking there is a 3-4% chance of fetuses suffering from genetic conditions.

If a prenatal screening result comes back as high risk, the second step is to go for what are known as Confirmatory Tests. These tests confirm if the fetus is indeed affected by a genetic abnormality which is reflected in the primary screenings.

Confirmatory or Definitive tests for checking chromosomal abnormalities are invasive and carry a risk of miscarriage. Prenatal Screenings help identify those pregnancies that are at a high risk of having a chromosomal abnormality hence warrant an invasive test. Those pregnancies that are reflect as low risk after a screening need not expose their pregnancy to undue harm by doing an invasive test.

Established practice across the world in developed countries is for all couples who are planning on conceiving or those who have already conceived to be offered Prenatal Screenings by their doctors. As screenings are predominantly woman focused, every woman planning or already pregnant should do this. It is recommended more so for
women of advanced maternal ages as they have increased risk of having babies with genetic abnormalities.

Since genetic diseases can either be passed on from a parent to child or occur spontaneously during conception without any previous family history, ACOG, RCOG, RANZCOG & various other international medical & gynaecological societies recommend that these screenings be done for all women.

Prenatal screenings first and foremost give expecting parents peace of mind by providing information of the health of their child much in advance. Secondly & more importantly, because genetic disorders are non-treatable, screenings give parents the choice & freedom to decide the outcome of their pregnancies & the future their loved ones. Also, opting for a Prenatal Screening will enable you to decide for or against an invasive confirmatory test.

The different types are:

i.                     First Trimester Screenings (FTS) done between 11-13.6 weeks of pregnancy. The screening done in this period is called:

a.       Dual Marker

b.      Dual Marker + Nuchal Translucency

ii.                   Second Trimester Screenings (STS) done between 15-20.6 weeks of pregnancy. The screenings done in this period are called:

a.       Triple Marker

b.      Quadruple Marker

iii.                  Integrated Screenings or Combined Screening: this is when FTS & STS are combined for higher accuracy & double checking.

a.       Integrated Screening

b.      Serum Integrated

Non Invasive Prenatal Testing (NIPT) done from 11 weeks onwards till birth: is a new, highly advance test with very high accuracy, nearly 99.5%. However according to Indian law, termination is allowed till 20 weeks. Hence, as such the window is after 11 weeks & before 18 weeks.

Choice of a screening test can be done based on multiple factors like the period of pregnancy you are in, availability of an ultrasound facility and socio-economic factors. Your doctor will be your best guide in helping you choose the screening test best suited to you.

Yes, if you wish to know the health of your unborn child & not take any chances.  As genetic disorders may not show up in routine checkups, it is impossible to know if the fetus is normal unless it is screened. Hence it is less of a need based requirement & more preemptive & preventive focused.

It is important to note that NOT all genetic & chromosomal disorders are inherited as some disorders occur spontaneously (de novo mutation) during conception; meaning no history of genetic disorders is even necessary for a child to suffer from one. Also, some inherited disorders do not show any signs or symptoms of their presence for generations together due to their recessive nature. This may erroneously be interpreted as ‘no family history of genetic disorders’. Which is why, across the globe in developed countries prenatal screenings are routine procedures.

If that is the case, one certainly needs to discuss this with their referring doctor. As prenatal screenings only give risk assessment for a given set of most commonly found genetic disorders in India, there are other less common ones which your doctor will need to request specifically for, in case there is a family history. These decisions are normally taken during the course of pregnancy when abnormalities are noted during routine checkups or when doctors are aware of a family history & want to rule out any chances of the fetus being abnormal. Downs Syndrome being the most common trisomy & also a de-novo chromosomal abnormality, having a history of Downs Syndrome in the previous pregnancy increases your chance of having a Downs syndrome in the subsequent pregnancy by 1%.  It is in the best interest of prospective parents to inform doctors about any family history of genetically inherited diseases to enable them to make informed decisions.

There are primarily two windows:

  • 11-13.6 weeks or in the First Trimester.
  • 15-20.6 weeks or in the Second Trimester.
  • For NIPT the window is 10-20 weeks.

It is important to note that though Prenatal Screenings can be done up to 20 weeks, decision making on a high risk result becomes difficult as termination of an abnormal pregnancy is prohibited by Indian law after 20 weeks.

Unfortunately, genetic disorders cannot be detected beyond the given time frames. Conducting tests outside the screening windows would be futile. Also, by Indian law, abortion is legal only up to 20 weeks, hence it is advisable to conduct a screening as early as possible.

Open neural t tube defect, disorders in sex chromosome – turner syndrome,

Chaitra to add Common chromosomal abnormalities like Downs syndrome, Edwards syndrome and Pataus syndrome are screened in prenatal screening. Besides these abnormalities prenatal screening also gives risks for certain non chromosomal abnormalities like Pregnancy induced hypertension ( Pre-eclampsia) & Open Neural Tube Defects.

You should be screened for the most common & widespread disorders which the test already do. In addition, if there is any family history then you will require additional tests specific to those disorders which your consulting doctor will decide.

In most cases than not, your referring doctor will request these tests for you. But if you wish to do so directly or through your doctor who isn’t familiar with Lilac Insights, you can directly Contact Us & we will facilitate the process.

For prenatal screening the only requirement is pregnancy. If you have multiple pregnancies, like twins or triplets, the screening modality will differ; you can get in touch with us or speak to your doctor for additional queries.

Regular blood drawn from the veins of the pregnant woman technically referred to as peripheral blood.

Normally one screening is all that is required. In some cases, especially for high risk results, doctors & patients might decide for an additional combined screening.

For the fetus & the mother, there are no risks.

Any trained phlebotomist or a nursing staff can draw the sample for the screening.

Genetic testing & diagnoses differs from ordinary pathology in several ways, mainly that medical genetics is a separate vertical within the field of medical sciences. The qualifications, background, expertise & technologies required to conduct & understand these tests are different from ordinary pathology. Importantly, the resultant reports are also not simple computer outputs & require human intervention. The screenings involve a complex process of measuring the levels, studying the patient demographics, correlating with ultrasound measurements and generating risk estimates by diligently integrating all of the above. Doctors & clinicians who do not have a genetic background are not medically equipped to address the complexities in the testing, diagnoses & interpretation of reports of genetic disorders.

No. Specialized labs like Lilac Insights which is a Genetic Health Assessment & Diagnostic Center will conduct prenatal screenings. Genetic screenings need well equipped technical labs and analytical support staff to perform the test and scientific experts to interpret the results.

Choosing the right genetic service provider is the first step to ensure your child’s future is in safe hands. You can click here to see Why Lilac Insights would be a good choice.

You may discuss this with your doctor & upon mutual agreement, provide us with the contact details. We will get in touch with the concerned person & facilitate the process. Being market leaders, there is a high chance that they are already working with us.

Prenatal screening reports give you a risk assessment of the fetus being genetically abnormal. As per international protocols 1/250 is taken as a cut off; in other words 0.4%.  If the pregnancy reflects anything higher than the cut off value, it is classified as high risk and anything below is low risk.

High risk implies the pregnancy is at a high risk of being affected with a genetic abnormality & the need for a secondary screening or a Confirmatory Test may be required. However, it does not completely exclude the possibility of the pregnancy being not affected with an abnormality & a residual chance of the fetus being completely normal still exists as the test is a ‘risk assessment’ & not a confirmation. This is known as False Positive.  False Positives are a rare chance & the threat to the fetus is considered as near certain; as in the case of Prenatal Screening, it is 3% for Lilac Insights: which means 3 in every 100 fetuses that are diagnosed as genetically abnormal are in fact not affected. The False Positive rate may vary for other labs depending on the technology, experts, protocols, guidelines & standardizations they follow. Keeping the False Positive rate as low as possible is important as it prevents unnecessary miscarriages due to invasive procedures of Confirmatory Tests. Lilac Insights has the lowest False Positive rate in the country. If you are still unsure, you may Contact Us or your doctor.

Low risk implies the pregnancy is at a low risk of being affected with a genetic abnormality & there is no secondary or confirmatory testing required. However, it does not completely exclude the possibility of the pregnancy being affected with an abnormality & a residual chance of fetus being affected still exists as the test is a ‘risk assessment’ & not a confirmation.  This is known as False Negative.  False Negatives are a rare chance to the point of being not considered as a threat; as in the case of Prenatal Screening, it is 3% for Lilac Insights: which means 3 in every 100 fetuses that are diagnosed as normal are in fact affected with a genetic disorder. The False Negative rate may vary for other labs depending on the technology, experts, protocols, guidelines & standardizations they follow. Lilac Insights has the lowest False Negative rate in the country. If you are still unsure, you may Contact Us or your doctor.

Your doctor should be able to address all your questions. You may feel free to get in touch with our genetic counsellors if you wish.

Screening normally takes about 1-2 days post arrival of blood sample at the lab. Your doctor should have a digital report by the end of the third day.

All pricings will be provided by your referring doctor.

For getting a screening done, the simplest way is to speak to your consulting Obstetrician or Gynecologist. As Lilac Insights is a market leader, there is a good chance they are already availing of our services. In the event your doctor is not familiar with Lilac Insights, upon mutual discussion you may provide us with your doctor’s details & we will get in touch with them to facilitate the process.

You may also Contact Us directly & we will guide you through the process.

Because Genetic Counselors are not easily available, Lilac Insight has developed a web based platform designed to conduct genetic counseling sessions from the comfort of the patient’s home or the doctor’s clinic. Its purpose is to reach people across the country & the globe, & to address queries that patients and doctors might have resulting from complex genetic scenarios.

The goal is to disburse knowledge, increase awareness and support families either affected by or are at risk of suffering from a genetic disorder.

Just Contact Us by phone or email & we will guide you through the process.

Feel free to Contact Us for additional questions.