Prenatal testing

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. These may be anatomic and physiologic problems with the health of the zygote, embryo, or fetus, either before gestation even starts 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 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 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. Birth defects have an occurrence between 1 and 6%.

Purpose

There are three purposes of prenatal diagnosis: to enable timely medical or surgical treatment of a condition before or after birth, to give the parents the chance to abort a fetus with the diagnosed condition, and 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.

	Name of test '	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
Routine prenatal tests	Maternal blood pressure/Preeclampsia screen	Every checkup appointment	Non-Invasive	Blood pressure cuff	Immediately	Pre-eclampsia/hypertension	NA
Routine prenatal tests	Maternal urinalysis/urine test screen	Periodically	Non-invasive	Urine collection	~a few minutes – ~1 week	hCG, diabetes, dehydration, preeclampsia, kidney and bladder infection/disease	NA
Routine prenatal tests	Ultrasound	Periodically	Non-invasive/Invasive	Abdominal or Transvaginal	~1 day – ~1 week	Fetal development, neural tube defects, birth defects, and various other physical abnormalities	NA
Routine prenatal tests	Fetal heart-rate monitoring	Week 12 – onward	Non-invasive	Handheld abdominal doppler or fetoscope	Immediately	Heart rate irregularities	NA
Genetic prenatal tests	Carrier screening	Anytime	Less invasive	Cheek swab or blood draw	~2–4 weeks	Determining if a parent carries specific genes associated with certain conditions	Very low risk, however there is the potential for bruising, pain, nerve damage, fainting, haematoma, bacterial infection, and bloodborne pathogen exposure.
Genetic prenatal tests	Chorionic villus sampling/Biopsy, CVS	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
Genetic prenatal tests	Cell-free fetal DNA Test/Noninvasive prenatal test	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.
Genetic prenatal tests	First trimester screening	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.
Genetic prenatal tests	Alpha-fetoprotein /modified sequential/multiple marker/quad/triple/maternal serum test	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.
Genetic prenatal tests	Second trimester screening	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.
Genetic prenatal tests	Amniocentesis	Week 15 – 20	Invasive	Transabdominal needle insertion to obtain an amniotic fluid sample	~2 weeks	Chromosomal abnormalities, autosomal genetic conditions, neural tube defects, abdominal wall defects, birth defects	Miscarriage, preterm labor/delivery, infection, cramping, bleeding, premature rupture of amniotic membrane
Genetic prenatal tests	Cordocentesis/Percutaneous umbilical cord blood sampling	Week 17 – onward	Invasive	Fetal blood sample from umbilical cord	~3 days	Chromosomal abnormalities, blood disorders	Miscarriage, preterm labor/delivery, infection, bleeding, decreased fetal heart rate, premature rupture of amniotic membrane, death
Genetic prenatal tests	Preimplantation genetic diagnosis	During IVF, prior to implantation	Non-invasive	IVF embryo examination	~1–2 weeks	Chromosomal abnormalities, autosomal recessive conditions	NA
Additional prenatal tests	Glucose challenge test	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.
Additional prenatal tests	Oral glucose tolerance test	Week 26 – 28	Less invasive	Maternal blood draws before and after ingestion 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.
Additional prenatal tests	Non-stress test	Week 28 – onward	Non-invasive	Abdominal contraction/Fetal heart rate belt	Immediately	Fetal heart rate vs movement, oxygen levels, fetal distress	NA
Additional prenatal tests	Group B Strep Test	Week 36 – 38	Invasive	Vaginal swab	~1–2 days	Bacteria indicating Group B Strep	NA
Additional prenatal tests	Cervix dialation check	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
Additional prenatal tests	External fetal monitoring	During Labor, after rupture of amnioatic sac	Invasive	Spiral wire electrode attached to body part of fetus via cervical insertion	Immediately	Heart rate irregularities, monitoring fetal heart rate	Fetal bruising/infection at attachment site
Additional prenatal tests	Kleihauer-Betke/Fetal cells in maternal blood test	Situational	Less invasive	Blood draw	<1 day	Fetal red blood cells in the mother's blood, fetomaternal hemorrhage	Very low risk, however there is the potential for bruising, pain, nerve damage, fainting, haematoma, bacterial infection, and bloodborne pathogen exposure.