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Chapters

0:00 Introduction
0:45 When to schedule it?
1:25 How to prepare for the prenatal appointment?
2:10 What to expect?


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, 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. Invasive procedures remain important, though, especially for their diagnostic value in confirming positive non-invasive findings and detecting genetic disorders. 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.[3]
Testing guidelines and qualifying risk factors for invasive testing

The American College of Obstetricians and Gynecologists guidelines currently recommend that anyone who is pregnant, regardless of age, should discuss and be offered non-invasive prenatal genetic screening and diagnostic testing options.[4] Non-invasive prenatal genetic screening is typically performed at the end of the 1st trimester (11–14 weeks) or during the beginning of the second trimester (15–20 weeks) and involves the pregnant woman receiving a blood draw with a needle and a syringe, and an ultrasound of the fetus. Screening tests can then include serum analyte screening or cell-free fetal DNA, and nuchal translucency ultrasound [NT], respectively.[5] It is important to note that screening tests are not diagnostic, and concerning screening results should be followed up with invasive diagnostic testing for a confirmed diagnosis. Invasive diagnostic prenatal genetic testing can involve chronic villus sampling (CVS) or amniocentesis.[6] The ACOG recommends genetic screening before pregnancy to all pregnant women planning to have a family.[7] After comprehensive counseling and discussion that acknowledges residual risks, it is important to respect the patients' right of choosing to pursue or not pursue any component of genetic testing.

The following are some reasons why a woman might consider her risk of birth defects already to be high enough to warrant skipping screening and going straight for invasive testing.[6]

Increased risk of fetal aneuploidy based on personal obstetric history or family history affected by aneuploidy
Increased risk for a known genetic or biochemical disease of the fetus
Maternal transmissible infectious disease such as rubella or toxoplasma
Parental request in the context of acute parental anxiety or under exceptional circumstances

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