A comprehensive guide to early-pregnancy screening: part 2

In the second article of a two-part series Dr Panicos Shangaris explains how ultrasound and blood tests can identify any potential issues in pregnancy and how they can help prospective parents to prepare to welcome their baby. 

How do ultrasound scans contribute to early pregnancy screening, and what information can be obtained from these scans?

Ultrasound scans are an essential part of early pregnancy care. They use high-frequency sound waves to create images of the developing foetus and the mother's reproductive organs.

Ultrasound scans can provide the following information:

Confirmation of pregnancy and its location

An early ultrasound can confirm the presence of an intrauterine pregnancy and rule out an ectopic pregnancy (when the fertilised egg implants outside the uterus, most commonly in the fallopian tube), which can be life-threatening if not treated promptly.

Determination of gestational age

Ultrasounds can accurately determine the stage of pregnancy, based on the size of the foetus and can be used to estimate the due date.

Confirmation of fetal viability

An ultrasound can confirm if the foetus is alive by detecting a heartbeat.

Multiple pregnancies

Ultrasound can determine if there is more than one foetus.

Examination of fetal anatomy

Even in early pregnancy, some basic assessments of fetal anatomy can be made. As pregnancy progresses, more detailed anatomical scans can be performed to check for fetal physical abnormalities.

Nuchal Translucency (NT) Screening

Around 11-14 weeks, an ultrasound is used for NT screening, which measures the thickness of space at the back of the baby's neck. An increased measurement can indicate a higher risk for genetic disorders like Down syndrome and other heart or body abnormalities.

Assessment of Maternal Structures

Ultrasounds can evaluate the uterus, ovaries, and cervix, identify conditions like fibroids or ovarian cysts, and monitor the length of the cervix, which can have implications for preterm labour.

Placental Assessment

The ultrasound can check the position of the placenta, which could be important for delivery if the placenta is covering the cervix (placenta previa), or if it is showing signs of early separation from the uterine wall (placental abruption).

While ultrasound is a valuable tool, its ability to detect anomalies or conditions depends on many factors, including the equipment's quality, the pregnancy stage, the foetus's position, and the operator's skill and experience. While many abnormalities can be detected through ultrasound, not all can, so it's just one part of comprehensive prenatal care.

Are there any specific blood tests that are routinely performed during early pregnancy, and what do they help to identify or monitor?

Several blood tests are typically performed during early pregnancy to assess the health of the mother and the developing foetus. Examples include:

Full Blood Count (FBC)

This test measures several components of the blood, including red and white blood cells and platelets. It can identify conditions like anaemia, infection, and clotting issues.

Blood Type and Rh Factor

This determines the mother's blood type (A, B, AB, or O) and Rh factor (positive or negative). If the mother is Rh negative and the baby is Rh positive, it can lead to Rh incompatibility, which can cause problems in subsequent pregnancies.

Rubella Immunity (screening ended under the NHS in April 2016)

This test checks if the mother is immune to rubella (German measles), which can cause birth defects if contracted during pregnancy.

 **Hepatitis B and C (HepC not routinely done in the NHS) Tests

These tests determine if the mother has hepatitis B or C viruses, which can be passed to the baby during delivery and cause serious health problems.

Syphilis Test

Syphilis is a sexually transmitted infection that can cause serious complications during pregnancy, including infant death. However, if identified, it can be treated.

HIV Test

HIV can be transmitted from mother to child during pregnancy, childbirth, or breastfeeding. If the mother tests positive, certain treatments can significantly reduce the risk of transmitting HIV to the baby.

Varicella Immunity (not done under the NHS)

This test checks for immunity to varicella (chickenpox). If the mother is not immune, she will be advised to avoid exposure and can be vaccinated after delivery.

Thyroid Function Test (not done under the NHS)

In some cases, especially if the woman has symptoms of a thyroid disorder or a history of thyroid disease, thyroid function tests may be performed.

Glucose Screening

This test for gestational diabetes is typically done between 24-28 weeks, but it might be done earlier if the woman has risk factors for gestational diabetes, such as obesity or a family history of diabetes.

Genetic Carrier Screening

This is typically offered when there is a family history of certain genetic conditions or based on certain ethnic backgrounds. It can determine if the mother is a carrier for conditions such as cystic fibrosis, spinal muscular atrophy, or certain conditions more prevalent in specific ethnic groups, like sickle cell disease.

These blood tests are important for identifying potential issues that could affect the health of the mother or baby. If problems are identified, appropriate treatments or interventions can be implemented to manage these conditions.

What are the potential benefits and limitations of early pregnancy screening tests, and how do they help in guiding further medical interventions or decisions?

Early pregnancy screening tests provide crucial information about the health of the pregnant individual and their developing baby.  However, as with any medical test, they have both benefits and limitations.

Benefits

Early Detection and Intervention

Screening tests can detect potential health issues in both the mother and baby early on, providing timely interventions, adjustments in care, or early treatment.

Informed Decision-Making

Screening results can inform parents about the likelihood of certain genetic or chromosomal conditions, which in turn helps them make informed decisions about additional testing, potential treatments, or preparation for a child with special needs.

Planning and Preparation

Test results can aid healthcare providers in providing plans for a safer delivery if certain conditions are identified, such as placenta previa or a baby with a heart defect, as well as helping parents prepare emotionally and practically for a baby with health issues or special needs.

Limitations

Not Diagnostic

Screening tests provide risk assessments rather than definitive diagnoses. They can identify if a pregnancy is at higher risk for certain conditions but cannot confirm the presence of these conditions.

False Positives and Negatives

There is a risk of false positives (the test indicates a problem when there isn't one) and false negatives (the test doesn't detect a problem that is present). This can cause unnecessary worry or provide false reassurance.

Can't Detect All Problems

While these tests can screen for several conditions, they can't identify all potential health problems. Some issues may not become apparent until later in pregnancy or after birth.

Risk of Procedure-Related Complications

While most screening tests are low risk, diagnostic tests performed following a positive screening result, such as amniocentesis or chorionic villus sampling (CVS) can carry a small risk of complications, including miscarriage.

In terms of guiding medical interventions or decisions, a high-risk result on a screening test can lead to further diagnostic testing, consultations with specialists, targeted monitoring, or specific interventions during pregnancy or at delivery. These decisions are made on an individual basis, taking into account the specific condition, the overall health of the pregnant person and foetus, the desires of the parents, and the healthcare team's advice.

If you are pregnant and would like to book a consultation with Dr Shangaris, simply visit  his Top Doctors profile today.