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| Prenatal testing | |
|---|---|
| Synonyms | Prenatal screening, Prenatal diagnosis, Genetic testing |
| Purpose | To monitor maternal and fetal health and progression, as well as, detect fetal abnormalities during pregnancy. |
Prenatal testing is a tool that can be used to detect some birth defects at various stages prior to birth. Prenatal testing consists of prenatal screening and prenatal diagnosis, which are aspects of prenatal care that focus on detecting problems with the pregnancy as early as possible.[1] These may be anatomic and physiologic problems with the health of the zygote, embryo, or fetus, either before gestation even starts (as in preimplantation genetic diagnosis) or as early in gestation as practicable. Screening can detect problems such as neural tube defects, chromosome abnormalities, and gene mutations that would lead to genetic disorders and birth defects, such as spina bifida, cleft palate, Down syndrome, trisomy 18, Tay–Sachs disease, sickle cell anemia, thalassemia, cystic fibrosis, muscular dystrophy, and fragile X syndrome. Some tests are designed to discover problems which primarily affect the health of the mother, such as PAPP-A to detect pre-eclampsia or glucose tolerance tests to diagnose gestational diabetes. Screening can also detect anatomical defects such as hydrocephalus, anencephaly, heart defects, and amniotic band syndrome.
Prenatal screening focuses on finding problems among a large population with affordable and noninvasive methods. Prenatal diagnosis focuses on pursuing additional detailed information once a particular problem has been found, and can sometimes be more invasive. The most common screening procedures are routine ultrasounds, blood tests, and blood pressure measurement. Common diagnosis procedures include amniocentesis and chorionic villus sampling. In some cases, the tests are administered to determine if the fetus will be aborted, though physicians and patients also find it useful to diagnose high-risk pregnancies early so that delivery can be scheduled in a tertiary care hospital where the baby can receive appropriate care.
Prenatal testing in recent years has been moving towards non-invasive methods to determine the fetal risk for genetic disorders. The rapid advancement of modern high-performance molecular technologies along with the discovery of cell-free fetal DNA (cffDNA) in maternal plasma has led to new methods for the determination of fetal chromosomal aneuploidies. This type of testing is referred to as non-invasive prenatal testing (NIPT) or as non-invasive prenatal screening. Invasive procedures remain important, though, especially for their diagnostic value in confirming positive non-invasive findings and detecting genetic disorders.[3] Birth defects have an occurrence between 1 and 6%.[4]
Purpose
There are three purposes of prenatal diagnosis: (1) to enable timely medical or surgical treatment of a condition before or after birth, (2) to give the parents the chance to abort a fetus with the diagnosed condition, and (3) to give parents the chance to prepare psychologically, socially, financially, and medically for a baby with a health problem or disability, or for the likelihood of a stillbirth. Prior information about problems in pregnancy means that healthcare staff as well as parents can better prepare themselves for the delivery of a child with a health problem. For example, Down syndrome is associated with cardiac defects that may need intervention immediately upon birth.[5]
| Name of Test (Category)' | When | Invasivity | How | Turnaround time | Tests/Screens for
~Associated risks | ||
|---|---|---|---|---|---|---|---|
| Routine prenatal tests | Maternal weight | Every checkup appointment | Non-invasive | Scale | Immediately | Baselines, pre-pregnancy weight estimates, tracking weight gain/loss, pattern observation | NA |
| Maternal blood pressure/Preeclampsia screen[6] | Every checkup appointment | Non-Invasive | Blood pressure cuff | Immediately | Pre-eclampsia/hypertension | NA | |
| Maternal urinalysis/urine test screen[7] | Periodically | Non-invasive | Urine collection | ~a few minutes - ~1 week | hCG, diabetes, dehydration, preeclampsia, kidney and bladder infection/disease | NA | |
| Ultrasound[8] | Periodically | Non-invasive/Invasive | Abdominal or Transvaginal | ~1 day - ~1 week | Fetal development, neural tube defects, birth defects, and various other physical abnormalities (see below for specific ultrasound tests) | NA | |
| Fetal heart rate monitoring[9] | Week 12 - onward | Non-invasive | Handheld abdominal doppler or fetoscope | Immediately | Heart rate irregularities | NA | |
| Genetic prenatal rests | Carrier screening (Screen)[10] | Anytime (before or during pregnancy) | Less invasive | Cheek swab or blood draw | ~2–4 weeks | Determining if a parent carries specific genes associated with certain (primarily autosomal recessive) conditions | Very low risk, however there is the potential for bruising, pain, nerve damage, fainting, haematoma, bacterial infection, and bloodborne pathogen exposure. |
| Chorionic villus sampling/Biopsy, CVS (diagnostic)[11] | Week 8 - 14 | Invasive | Transabdominal or transcervical insertion of a needle, forceps or syringe to obtain a fetal placenta tissue sample | ~1–2 weeks | Chromosomal abnormalities, birth defects | Miscarriage, preterm labor/delivery, infection, cramping, bleeding, premature rupture of amniotic membrane, baby limb defects | |
| Cell-free fetal DNA (cfDNA) Test/Noninvasive prenatal test (NIPT) (screen)[12] | Week 10 - onward | Less invasive | Blood draw | ~1–2 weeks | Gender, chromosomal abnormalities | Very low risk, however there is the potential for bruising, pain, nerve damage, fainting, haematoma, bacterial infection, and bloodborne pathogen exposure. | |
| First trimester screening[13] | Week 10 - 13 | Invasive | Nuchal translucency ultrasound & blood prick/draw | ~1 week | Chromosomal abnormalities, birth defects, heart defects | Very low risk, however there is the potential for bruising, pain, nerve damage, fainting, haematoma, bacterial infection, and bloodborne pathogen exposure. | |
| Alpha-fetoprotein (AFP)/modified sequential/multiple marker/quad/triple/maternal serum test (screen)[14] | Weeks 14 - 22 | Less invasive | Blood draw | ~1–2 weeks | Maternal hormone levels, risk of gestational hypertension and preeclampsia, chromosome abnormalities, neural tube defects | Very low risk, however there is the potential for bruising, pain, nerve damage, fainting, haematoma, bacterial infection, and bloodborne pathogen exposure. | |
| Second trimester screening (screen)[15] | Week 15 - 22 | Invasive | Ultrasound and multiple markers or quad screen blood draw | ~1–2 weeks | Chromosomal abnormalities, neural tube defects, abdominal wall defects, heart defects, other major physical defects | Very low risk, however there is the potential for bruising, pain, nerve damage, fainting, haematoma, bacterial infection, and bloodborne pathogen exposure. | |
| Amniocentesis (diagnostic)[16][17] | Week 15 - 20 | Invasive | Transabdominal needle insertion to obtain an amniotic fluid sample | ~2 weeks | Chromosomal abnormalities, autosomal recessive conditions, neural tube defects, abdominal wall defects, birth defects | Miscarriage (1%), preterm labor/delivery, infection, cramping, bleeding, premature rupture of amniotic membrane | |
| Cordocentesis/Percutaneous umbilical cord blood sampling (PUBS) (diagnostic)[18] | Week 17 - onward | Invasive | Fetal blood sample from umbilical cord | ~3 days | Chromosomal abnormalities, blood disorders (fetal hemolytic disease) | Miscarriage (1-2%), preterm labor/delivery, infection, bleeding, decreased fetal heart rate, premature rupture of amniotic membrane, death | |
| Preimplantation genetic diagnosis (PGD) (screen)[19] | During IVF, prior to implantation | Non-invasive | IVF ebryo examination | ~1–2 weeks | Chromosomal abnormalities, autosomal recessive conditions | NA | |
| Additional prenatal tests | Glucose challenge test (screen) | Week 26 - 28 | Less invasive | Maternal blood draw after ingestion of glucose drink | ~1–2 days | To indicate the possibility of gestational diabetes | Very low risk, however there is the potential for bruising, pain, nerve damage, fainting, haematoma, bacterial infection, and bloodborne pathogen exposure. |
| Oral Glucose Tolerance Test (Screen)[20] | Week 26 - 28 | Less invasive | Maternal blood draws before and after injestion of glucose drink, requires fasting | ~2–3 days | To properly diagnose gestational diabetes following an abnormal result from the glucose challenge screen | Very low risk, however there is the potential for bruising, pain, nerve damage, fainting, haematoma, bacterial infection, and bloodborne pathogen exposure. | |
| Non-stress test[21] | Week 28 - onward | Non-invasive | Abdominal contraction/Fetal heart rate belt | Immediately | Fetal heart rate vs movement, oxygen levels (indicating problems stemming from the placenta or umbilical cord), fetal distress | NA | |
| Group B Strep Test[22] | Week 36 - 38 | Invasive | Vaginal swab | ~1–2 days | Bacteria indicating Group B Strep | NA | |
| Cervix dialation check[23] | Week 37 - onward | Invasive | The doctor takes a manual measurement inside the cervix | Immediately | Signs or progress of dialation, prodromal labor | Infection, premature rupture of amniotic membrane | |
| External fetal monitoring[9] | During Labor, after rupture of amnioatic sac | Zdroj:https://en.wikipedia.org?pojem=Prenatal_diagnosis
