DNA testing during pregnancy

Written by Rebecca Fishwick
21 January 2019

Until relatively recently, parents had to wait until the birth of their baby to find out the sex, the potential health concerns, and sometimes the paternity of their child. But with DNA testing becoming more accessible, and with analysis techniques continuing to advance, it is now possible to learn a significant amount of information about your unborn child through prenatal DNA testing – all before you reach your second trimester.

There are three types of DNA tests that you can take while pregnant: prenatal paternity tests, foetal sex tests (sometimes advertised as “baby gender tests”), and prenatal screening tests. With these tests now available to the public, you can achieve peace of mind about the father of your child, prepare for your son or daughter, and – if your child is likely to be born with a health condition – make sure they receive the best possible care before they enter the world.

Before taking a prenatal DNA test, it’s important to know exactly what information you’ll be provided with, and what you are or are not able to find out.

Prenatal Paternity Tests

It is now possible to confirm the biological father of an unborn child through a prenatal paternity test. Taking a paternity test while pregnant can help to reduce stress by removing uncertainty, and allow you to make care and visitation arrangements early on.

Non-Invasive Prenatal Paternity Tests

Non-Invasive Prenatal Tests (often shortened to “NIPT”) for paternity can be taken from 10 weeks in pregnancy, measured from the Last Menstrual Period (LMP). These DNA tests analyse the cell-free foetal DNA present in the mother’s blood from a few weeks into pregnancy, and compare it with DNA from a cheek swab sample given by the potential father in order to test for paternity.

Potential fathers can take the cheek swab samples themselves at home. However, the mother’s blood sample will have to be collected by a trained medical professional. This may incur an extra cost, and you may have to arrange an appointment with your medical practitioner yourself.

Things to bear in mind
When conducted properly, prenatal paternity tests are 99.99% accurate; the same level of accuracy as normal paternity tests. However, regulation of prenatal DNA tests is currently very limited, and so there are some companies that offer substandard testing with the promise of 99% accuracy.

Here are some things to watch out for when choosing a prenatal paternity testing company:

• Cheap prices. Prenatal paternity tests are expensive. Really expensive. It costs a lot for the lab to conduct these tests, so expect to pay somewhere in the range of £1000 or more, and beware of tests offering prices that are obviously undercutting their competitors’. If the price seems too good to be true, it probably is.

• Hidden costs. Again, prenatal paternity tests are expensive. Companies will sometimes try to hide the full cost by charging different amounts at different stages of the testing process. For instance, you may have already paid to submit your samples, but then have to pay a lab fee in order to begin testing or receive your results. Some companies will deliver results over the phone, but then charge extra for written results.

• If they allow you to take the blood sample yourself. The blood sample will need to be taken by a trained medical practitioner, and you will often have to arrange this yourself (which may incur an extra cost). The testing company you use may arrange a collection for you, though there will probably be another charge for this. Any company that allows you to take a blood sample yourself, particularly if they ask only for a blood sample on card (using a finger-pricking device), will not deliver accurate results.

• If they allow you to take the test earlier than 10 weeks into pregnancy. The earliest you can take a prenatal paternity test is 10 weeks from your Last Menstrual Period (LMP). Tests taken earlier than 10 weeks will not yield accurate results.

• If they let you submit “discreet” samples. Some companies will allow you to submit “discreet” samples of the potential father’s DNA, such as cigarette butts or tissues. This will greatly affect the accuracy of the results. It is also sometimes a red flag that a company is not very reputable. In some countries – including the UK – it is illegal to test a person’s DNA without their consent, and doing so could lead to legal action.

• The quality of the company’s website. It may not seem important, but if a company’s website is obviously outdated, has a lot of bugs, is difficult to navigate, looks pixilated and grainy, has a lot of poorly formatted graphics, or isn’t HTTPS encrypted – then you ought to consider the possibility that they aren’t running a legitimate operation. Think of it this way: if they can’t afford a good website, then they probably can’t afford a good lab.

This may all seem like a lot of information to consider, but as prenatal paternity tests are still relatively new, many people don’t know what they ought to look out for, and don’t realise that the sale of these tests is largely unregulated. Make sure you are as informed as you can be before purchasing a prenatal paternity test.

Providers we recommend for NIPT paternity tests are:
• DNA Diagnostics Center
• Easy DNA
• Alpha Biolabs
• International Biosciences

You can find a list of more providers offering non-invasive prenatal paternity tests here.

Invasive Prenatal Paternity Tests

As well as the non-invasive method, there are two types of invasive prenatal tests you can take to test paternity. These are CVS (Chorionic Villi Sampling) and amniocentesis.

A CVS test involves a needle being inserted into the placenta, either through the stomach or the cervix, to extract a small number of cells from a section known as the chorionic villi. This is usually done under local anaesthetic, and is always carried out by a trained medical professional. CVS tests can be carried out after 11 weeks into pregnancy.

The other method, amniocentesis, is a similar procedure, but amniotic fluid is collected instead of a sample from the chorionic villi. Amniocentesis can be carried out 15 weeks into pregnancy.

It is unlikely you will ever be recommended an invasive procedure unless it is for a health concern that has already been non-invasively tested for. However, some companies do offer this as a method of conducting a paternity test while pregnant.

Both of these invasive methods for testing paternity carry a small – though not insignificant – risk of miscarriage. Studies from the 1970s put the risk at about 1 in 100 for CVS, and 1 in 200 for amniocentesis. However, a more recent meta-analysis estimated the risk of miscarriage to now be closer to 1 in 500 for CVS, and 1 in 1000 for amniocentesis.

Some people may be tempted to opt for an invasive test due to the cheaper cost compared to non-invasive tests. However, these procedures must be carried out by trained medical professionals, and so the medical costs they incur could make them as expensive as non-invasive tests, or perhaps more so.

Prenatal Sex Testing / Baby Gender Testing

Unlike prenatal paternity tests, foetal sex tests can be conducted as early as seven weeks into pregnancy, measured from the Last Menstrual Period. These tests look for cell-free foetal DNA (cffDNA) belonging to the foetus, which can be detected in the mother’s blood. These tests are 95-98% accurate from 7-20 weeks, with their accuracy rising to 97-99% after 20 weeks. Usually, these tests are only offered after 10 weeks, possibly to improve the accuracy.

Often, you will not have your first ultrasound until 14 weeks into pregnancy, and so it is sometimes possible to determine your baby’s sex before your first ultrasound using a DNA test. These tests are not a replacement for an ultrasound test, which is important for monitoring your unborn baby’s health and development, and predicting your due date.

Like non-invasive prenatal paternity tests, a prenatal sex DNA test requires a blood draw taken by a trained medical professional. The blood sample taken will not be as large as for a paternity test, since less foetal DNA is needed to determine sex. Still, beware of companies that offer baby gender tests that require you to only prick your finger onto card, or draw the blood yourself. These will not yield accurate results.

Prenatal sex tests look only for the presence of a Y chromosome, which would indicate a boy. If no Y chromosome is detected, then it is highly probable the baby will be a girl. You will typically receive results within two weeks. As prenatal sex testing is far less complicated than prenatal paternity testing, it is also far less expensive, costing around £200.

For prenatal sex tests, we recommend International Biosciences. Other testing providers can be found here.

Limitations of foetal sex testing
It is important to note that if you have suffered a miscarriage in the same year as your current pregnancy, your results may be affected by residual cell-free DNA from your previous pregnancy. Prenatal blood tests are not able to distinguish between cell-free DNA from a current or previous pregnancy.

If you are carrying twins, then a DNA test on the mother’s blood will only be able to tell you if you are carrying at least one boy (if a Y chromosome is detected) or if you are carrying only girls (no Y chromosome). So, if a Y chromosome is detected, you may be carrying only boys, or a boy and a girl.

Ethical implications of foetal sex testing
There have been concerns that foetal sex tests may be used – and have already been used – to abort foetuses based on sex selection. In some countries, such as China and India, prenatal genetic tests for sex have been banned for fear that pregnancies will be terminated in favour of having male children. In the UK, it is illegal to abort a pregnancy on the basis of foetal sex.

Prenatal Screening DNA Tests

Most healthcare providers only screen for only Down’s syndrome (also called Trisomy 21), Edward’s syndrome (Trisomy 18), and Patau’s syndrome (Trisomy 13). This screening is performed using a blood test offered 10-14 weeks into pregnancy, and looks for the proteins and hormones associated with these conditions.

Studies have shown that testing the baby’s DNA can more accurately predict whether he or she will be born with one of these conditions. In fact, it has been estimated that the protein- and hormone-based blood test for Down’s syndrome predicts the condition with 85-90% certainty, which includes 2.5% “false positive” results. False positives are an important issue because a positive prediction often leads to the termination of the pregnancy. However, DNA tests using the mother’s blood are thought to be 98% accurate, and to result in fewer false positives.

You can take a DNA screening test from about 10 weeks into pregnancy. Private prenatal health screening usually costs around £1000. Currently, relatively few providers offer this type of prenatal testing, which may be part of the reason why the service is so expensive, as well as the laboratory costs involved in extracting foetal DNA.

Like prenatal paternity and sex tests, prenatal screening tests require blood to be drawn from the mother by a medical professional, which is another reason why the cost is relatively high. Still, you may have to cover the medical costs separately.

You’ll typically receive the results of your screening test in about two weeks.

Ethical implications of prenatal screening
Some people have voiced concerns that the NIPT screening tests may result in people with Down’s syndrome disappearing from society. In Denmark and Iceland, where screening is almost universal, the abortion rate of foetuses likely to have Down’s syndrome is close to 100%.

In the UK, there are concerns that private clinics offering genetic screening may not provide the same amount of information and counselling as the NHS, meaning that parents may not understand the implications of genetic screening tests, or feel they do not have adequate support in moving forward with the information they are given. If you opt for a prenatal screening test with a private company, it is a good idea to look into what support they offer, and to learn as much as you can about the testing process, and the conditions being tested for.