13 prenatal screening tests to know

Screening tests provide valuable info on your baby's health, such as whether he has certain birth defects. We have details.

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Pregnancy is a time of highs and lows ― you’re excited because you can’t wait to meet your baby, but at the same time, you worry because you hope bubba will be born healthy.

Indeed, the median age of women in Singapore giving birth for the first time is age 30+. It’s also a fact that babies of late-in-life mothers — mothers above the age of 35 — may face an increased risk of chromosomal conditions like Down syndrome.

Dr Dharshini Gopalakrishnakone, an obstetrician and gynaecologist specialist at the Obstetrics & Gynaecology Centre Novena, says, “It is important to undergo prenatal tests as these tell us, with varying sensitivity, the likelihood of having a child with [health conditions]. Having this knowledge gives the parents options on how to manage the pregnancy as well as the baby after delivery.”

Incidentally, an all-clear in terms of screening results doesn’t mean you and baby are off the hook either. Dr Dharshini adds that these tests do not cover other genetic, structural or neurological conditions that may only be discovered later in the pregnancy or after birth.

Babies of late-in-life mothers — mothers above the age of 35 — may face an increased risk of chromosomal conditions like Down syndrome.

Not all the tests listed are compulsory, however, SmartParents ob-gyn expert Dr Christopher Chong, notes that if cost isn’t a concern, it’s best to go for the most accurate prenatal tests. Do ask your doctor about:

First Trimester

CHORIONIC VILLUS SAMPLING
WHEN Between 10 and 13 weeks.
WHAT Commonly referred to as CVS testing, your doc will extract chorionic villi samples from the placenta through your cervix or abdominal wall. Chorionic villi cells hold the genetic makeup of your growing baby.
WHY Tests will detect if your baby suffers from any genetic defects such as Down syndrome.
RISKS Dr Chong warns that the procedure does carry a 1 to 4 per cent risk of miscarriage. This risk can increase if the baby is smaller in size than usual for his age.

DATING SCAN
WHEN Between 11 and 13 weeks.
WHAT Your first ultrasound scan. Your sonographer may advise you to come with a full bladder so that they can obtain a clearer image.
WHY It’ll detect your stage of pregnancy based on the foetus’ physical development, so as to determine your child’s estimated date of delivery. You’ll also know if the foetus is growing in the right place or position, as well as be alerted if you are expecting more than one baby.

Read on to find out what prenatal tests to do during your second trimester…

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Second Trimester

COMPULSORY BLOOD TEST
WHEN Anytime during second trimester.
WHAT Detects presence of any sexually-transmitted diseases, HIV or Hepatitis B, plus confirm your blood group and Rhesus factor. Includes a full blood count to evaluate your general health.
WHY To determine if there are any blood disorders that might potentially be harmful for baby’s health. The Rhesus factor reveals the presence of the blood protein — D-antigen — in one’s body. If you have a negative result ― which means you do not have the blood protein — while your baby has it, complications may arise for your baby. This is because the protein may be misconstrued as infection, causing your white blood cells to attack it. If this is so, your doctor will need give you a routine dose of anti-D immunoglobulin to prevent it from happening.

NUCHAL TRANSLUCENCY TEST
WHEN Between 11 and 14 weeks. The test must be carried out by the end of week 13 as the foetus’ neck is no longer translucent at 14 weeks.
WHAT Otherwise referred to as a NT-Test, an ultrasound scan will ascertain with up to 80 per cent accuracy your baby’s risk of Down syndrome or any major congenital heart conditions. The scan measures the clear space within the tissues at the back of your baby’s neck ― any abnormalities is seen in the higher amounts of fluids in the cells.
WHY Lets you know ― especially for mothers who are aged 35 or older ― if your baby suffers from a genetic defect such as Down syndrome. This can also confirm the positive results of a CVS test.

ONE-STOP CLINIC FOR ASSESSMENT OF RISK TEST
WHEN Between 11 and 14 weeks.
WHAT Also known as the OSCAR test, which has about 80 to 90 per cent accuracy. A blood test, along with a neck and nose ultrasound scan, measures your baby’s risk of Down syndrome. Your blood will be drawn and analysed for its beta-hCG (produced as a result of your pregnancy) and pregnancy-associated plasma protein A (PAPP-A) levels. Low levels of beta-hCG are a common sign of an ectopic pregnancy, while reduced PAPP-A levels may suggest an abnormal number of chromosomes.
WHY Detects if your baby suffers from a genetic defect such as Down syndrome, especially useful for mothers aged 35 and above. This will confirm the positive result of a CVS or NT test.

The scan measures the clear space within the tissues at the back of your baby’s neck ― any abnormalities is seen in the higher amounts of fluids in the cells.

MATERNAL SERUM SCREENING TEST
WHEN From 15 weeks.
WHAT Also known as the Triple test. This blood test measures three hormones — alpha-fetoprotein, human chorionic gonadotrophin and oestriol — in the blood to determine the baby’s risk of developing Down and Edward syndromes, as well as a neural tube defect. Done together with the NT test, it has an accuracy of about 80 to 90 per cent, Dr Chong notes.
WHY To determine if your baby suffers from a genetic defect such as Down syndrome, especially helpful for mothers aged 35 and up. This will confirm the positive result of a CVS or NT test.

FOETAL ABNORMALITY SCAN
WHEN Between 20 and 22 weeks.
WHAT Also known as an FA Scan, this ultrasound scan is carried out by your sonographer to spot any physical abnormalities in your baby.
WHY The scan gives a detailed look at the baby’s bones, heart, brain, spine and kidneys. The scan can also uncover unusual deformities like a cleft lip and palate, a hole in the heart, a brain cyst and even a low-lying placenta, which can give rise to birth complications.

AMNIOCENTESIS
WHEN Usually done between week 16 and 20.
WHAT Fluid will be drawn from your water bag under ultrasound guidance. Usually prescribed when the previously mentioned tests have uncovered a high risk of Down syndrome or other abnormalities.
WHY To detect if your baby suffers from any genetic defects such as Down syndrome, which is helpful for mothers aged 35 and up. Dr Chong says this test is the “gold standard” as it has an accuracy of 99.9 per cent.
RISKS Dr Chong points out that the procedure carries a one in 200 chance of miscarriage. The risk can increase if the baby is smaller in size than usual for his age.

Read on to learn what the recommended third trimester tests are…

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Third Trimester

FOETAL GROWTH SCAN
WHEN Between 28 and 32 weeks.
WHAT An ultrasound and Doppler scan to check that your baby is growing and positioned normally for labour.
WHY Your doctor can check the position of the umbilical cord and measure the amount of amniotic fluid. If the foetus is not thriving, the doctor may recommend early delivery after assessing the amount of pressure on and blood flow to the foetus.

ORAL GLUCOSE TOLERANCE TEST
WHEN From 28 weeks, unless your doctor indicates otherwise.
WHAT Also known as OGTT, the test measures the body’s ability to absorb and use glucose, a type of sugar. Checks for gestational diabetes, which tends to occur in women who have a family history of the disease, are aged over 25, or obese (have a Body Mass Index of more than 30).
WHY Gestational diabetes can lead to high blood pressure and preeclampsia, which threatens both the mother’s and baby’s health. Gestational diabetes can also give rise to low blood sugar in your baby after birth, causing seizures. He is also has a higher risk of developing Type 2 — obesity-related — diabetes as a result of your gestational diabetes.

Gestational diabetes can lead to high blood pressure and preeclampsia, which threatens both the mother’s and baby’s health.

PLACENTAL POSITIONING SCAN
WHEN Between 28 and 32 weeks.
WHAT Dr Chong says this scanning test is done to ensure that the placenta is not obstructing the birth passage. If it is, your gynaecologist might arrange that you deliver by C-section.
WHY The placenta is a critical organ that supplies oxygen and removes waste from your baby’s blood. It attaches itself to wall of the uterus and is connected to your baby via the umbilical cord. However, in some cases, the placenta can be incorrectly positioned, leading to complications:

* Placenta previa The placenta covers the cervix partially or totally. It can cause severe vaginal bleeding before and during delivery.
* Placenta abruption The placenta peels away from the uterus wall partially or completely, causing cramps, pain or vaginal bleeding.

Right Before Labour

CARDIOTOCOGRAPH
WHAT A CTG machine monitors and measures the baby’s heartbeat over a 20-minute period and keeps track of the contractions of your womb.

AMNIOTIC FLUID INDEX TEST
WHAT Estimates the amount of amniotic fluid in the water bag. Amniotic fluids protect your foetus from getting hurt should you sustain a blow to your tummy. It also guards your unborn baby from infection, while letting his lungs and digestive system mature. A low water level can endanger your little one’s health.

Dr Dharshini Gopalakrishnakone is an obstetrician and gynaecologist specialist at the Obstetrics & Gynaecology Centre Novena and Dr Christopher Chong is a consultant obstetrician and gynaecologist at Gleneagles Hospital.

Photos: iStock

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