Purpose of Screening

• To assess gestational age, age is evaluated based on the length from the head to the buttocks (CRL), head width (BPD), and femur length (FL).

• Check the number of fetuses.

• Measure nuchal thickness, measure biochemical markers in the blood to perform integrated risk assessment for those women who wish.

• Examine the appearance of the fetus as well as possible at this stage.

• Note that about 3% of women receive confirmation of miscarriage during this examination.

Nuchal thickness

Nuchal thickness appears on the ultrasound as a black area (fluid) under the skin at the back of the fetus's neck.

All fetuses have some fluid in this area at this stage of pregnancy. It is usually a temporary accumulation of edema and a normal physiological phenomenon while part of the fetal heart and vascular system is forming.

However, if nuchal thickness is increased beyond the limits set according to gestational age, there is an increased risk that the fetus may have chromosomal abnormalities or other problems.

It should be noted that increased nuchal thickness is an indication of a problem but not a diagnosis. In certain cases, further tests may be offered to diagnose heart defects or chromosomal abnormalities.

Biochemical markers

Measurement of biochemical markers is done through a blood test that measures two proteins, free B-hCG and PAPP-A.

These are normal proteins during pregnancy and are transmitted from the placenta and fetus into the blood of the expectant mother.

Their levels in the blood vary during pregnancy, but deviations can indicate chromosomal abnormalities or other pregnancy-related risks, such as growth restriction or high blood pressure.

Results from fetal screening with integrated risk assessment

Results from the aforementioned tests, along with age and gestational length, are used together to calculate an individual integrated risk assessment for trisomy 21 (Down syndrome), trisomy 13 (Patau syndrome), and trisomy 18 (Edwards syndrome).

Results from the ultrasound are available immediately, while results from the blood test are available within two to three days, providing a final answer from the integrated risk assessment.

About 95-98% of women undergoing fetal screening with integrated risk assessment receive normal results, indicating no increased risk of fetal defects and no need for further investigations at this stage.

Results

Results are sent to the health center (maternal care) and to Heilsuvera. Women are offered further fetal screening at 20 weeks.

If expectant parents request a consultation despite results being below risk thresholds, it is easily arranged.

Further investigations

Results for about 2-5% of women indicate increased chances of chromosomal abnormalities or other fetal defects.

The midwife will contact those women who have increased risks and offer them further investigations and/or a consultation with an obstetrician/genetic counselor.

Criteria for increased risk:

• Trisomy 21 (Down syndrome): more than 1:100

• Trisomy 13 (Patau syndrome) and 18 (Edwards syndrome): more than 1:50.

These women are offered chromosomal testing, which involves sampling from the placenta or amniotic fluid.

The investigation provides a definitive result. However, it carries a risk of miscarriage, which is 0.5-1%.

If the risk of trisomy 21 is between 1:50-1:300, women are offered a more specific blood test, NIPT (non-invasive prenatal testing).

The sensitivity of the integrated test is considered to be up to 85-90%, meaning that if chromosomal testing were conducted on all fetuses diagnosed with a risk greater than 1:100 for trisomy 21 and 1:50 for trisomy 18 and 13, up to 85-90% of these chromosomal abnormalities would be detected.

It is noted that the integrated risk assessment provides statistical probabilities for trisomy 13, 18, and 21.

The sensitivity of NIPT is up to 99% for these trisomies, as it analyzes fetal DNA in maternal blood.

If nuchal thickness measures greater than 3.5 mm, a fetal heart ultrasound is offered at 20 weeks by pediatric cardiologists.

Major fetal defects detected in fetal screening at 11-14 weeks

• Anencephaly is a severe defect in the central nervous system, and the baby usually dies shortly after birth.

• Holoprosencephaly is also a severe defect in the central nervous system, and the baby often dies shortly after birth.

• Abdominal wall defects (gastroschisis, omphalocele). An opening in the abdominal wall that can be repaired with surgery after birth. Omphalocele is sometimes associated with chromosomal abnormalities.

• Urinary tract defects. The most severe cases can lead to death.

• Heart defects

• Limb defects

• Fetal hydrops (hydrops fetalis) is a severe problem, and the prognosis for the baby is poor.

Purpose of Screening:

• Assess gestational age

• Locate the placenta

• Evaluate amniotic fluid volume

• Identify fetal defects

At this time, the fetus is about 24 cm long and weighs about 300 g. The appearance of the fetus can be assessed more accurately than at 11-14 weeks, as the fetus is larger and it is easier to examine individual organs.

Gestational age is calculated based on the size of the head and femur. If an ultrasound has previously been performed at 11-14 weeks, the gestational age is confirmed; however, if it is the first ultrasound, an expected due date is provided.

The sex of the fetus is usually visible during the ultrasound at 19-20 weeks, but this is only examined if the mother requests it.

Multiple pregnancies are identified if no previous ultrasound has been performed. It is important to identify the placental and membrane separation in multiple pregnancies, as this has implications for monitoring later in the pregnancy.

The location of the placenta is examined. About 4% of women have a low-lying or previa placenta at 19-20 weeks.

In such cases, a follow-up ultrasound is recommended at 34 weeks. It is expected that about 10% of women will still have a low-lying or previa placenta at that time.

However, in 90% of cases, the placenta has moved upward as the uterus enlarges. During the 19-20 week ultrasound, fetal defects are detected in approximately 2% of women, and miscarriage is identified in about 0.5%.

The Following Parts Are Primarily Examined

On the Head:

• Skull bones

• Brain cavities

• Cerebellum

On the Face:

• Eye sockets

• Eyeballs

• Facial bones

• Lips

In the Chest Cavity:

• Heart

In the Abdominal Cavity:

• Stomach

• Kidneys

• Bladder

• Umbilical cord attachment

• Vessels in the umbilical cord

• Abdominal wall

On the Spine:

• Longitudinal section

• Cross-section

On the Limbs:

• Long bones are examined, and the femur and humerus are measured; consistency with head measurements is checked.

• Fingers and toes are not counted.

Major Fetal Defects Detected During Fetal Screening and Diagnosis at 11-14 and 19-20 Weeks of Pregnancy:

Chromosomal Abnormalities Detected Through Chromosomal Testing:

• Trisomy 21, which causes Down syndrome, is the most common chromosomal abnormality in children. Trisomy 21 means that there is an extra chromosome number 21. Individuals with Down syndrome have mild structural defects and are also at increased risk for congenital anomalies in organs, primarily in the heart and digestive tract. Their intelligence is variably impaired. Advances in treatment and support options have improved the outlook for individuals with Down syndrome and their life expectancy.

• Trisomy 13 (Patau syndrome) and Trisomy 18 (Edwards syndrome). Individuals with these extra chromosomes have developmental delays with growth disturbances and often malformations of organs, such as heart defects. The vast majority of fetuses with trisomy 13 or 18 die during pregnancy or shortly after birth.

• Monosomy XO – Turner syndrome. Individuals with one X chromosome have growth disturbances, infertility, and variably severe structural defects, although these rarely lead to severe disabilities. Most often, miscarriage occurs.

• Triploidy is an extra set of all chromosomes (a total of 69 chromosomes). An individual with triploidy has severe malformations and cannot survive.

• Other chromosomal abnormalities can also be detected.

Other Defects:

• Heart Defects. The more severe the heart defect, the greater the likelihood it will be detected before birth. It can be expected that most major heart defects will be identified during pregnancy, which is very important for preparing for the birth and the initial treatment thereafter.

• Anencephaly is a severe defect in the central nervous system, and the baby usually dies shortly after birth.

• Holoprosencephaly is also a severe defect in the central nervous system, and the baby often dies shortly after birth.

• Other central nervous system defects, such as spina bifida and hydrocephalus. These vary in severity but are always associated with some level of disability.

• Abdominal Wall Defects (gastroschisis, omphalocele). An opening in the abdominal wall that can be repaired with surgery after birth. This is sometimes associated with chromosomal abnormalities.

• Urinary Tract Defects. These vary in severity, ranging from mild issues that require no specific treatment and resolve after birth to severe impairment of kidney function that can lead to death.

• Fetal Hydrops (hydrops fetalis) is a serious problem, and the prognosis for the baby is poor.

• Clubfoot. Sometimes associated with other problems, but if no other issues are present, the prognosis is good. The child will need treatment after birth.

• Dwarfism. A variably severe condition that sometimes leads to death.

• Cleft Lip. Associated with heart defects and sometimes other problems. If no other issues are present, the prognosis is good, but the child will require surgery after birth.