| Method | Description | Risks, Concerns, and Indications |
|---|
| Preconception blood tests | Test for nutrients (especially iron); for diseases (syphilis, HIV, herpes, hepatitis B); for carrier status (cystic fibrosis, sickle-cell anemia, Tay-Sachs disease, thalassemia, etc.). | Might require postponement of pregnancy for counselling, treatment. |
| Pre-implantation testing | After in vitro fertilization, one cell is removed from each zygote at the four- or eight-cell stage and analyzed. | Not entirely accurate; requires in vitro fertilization and rapid assessment, delaying implantation. Used when couples are at high risk of known, testable disorders. |
| Tests for pregnancy-associated plasma protein A (PAPPA) and human chorionic gonadotropin | Blood tests are usually done at about 11 weeks to indicate levels of these substances. | Low levels correlate with chromosomal miscounts and slow prenatal growth, but falsepositive or false-negative results can occur. |
| Alpha-fetoprotein assay | Blood is tested for alpha-fetoprotein (AFP) level, often combined with other blood tests and repeat sonogram. | High AFP indicates neural-tube defects or multiple embryos; low AFP indicates Down syndrome. Normal levels change weekly; accurate conception dating required. |
| Sonogram (ultrasound) | High-frequency sound waves produce a “picture” of the fetus, often done several times, from 6 to 38 weeks. Detects many problems, anticipates complications. | Reveals head or body malformations, excess brain fluid, Down syndrome (via fetal neck measurement), and several diseases. Estimates fetal age and growth, reveals multiple fetuses and placental position. No known risks, unlike the X-rays that it has replaced. |
| Chorionic villus sampling (CVS) | A sample of the chorion (part of the placenta) obtained (via sonogram and syringe) at 10 weeks and analyzed. Cells of placenta are genetically identical to fetal cells, so CVS indicates genetic conditions. | Can cause spontaneous abortion (rare). |
| Amniocentesis | Some fluid inside the placenta is withdrawn (via sonogram and syringe) at 16 weeks; cells cultured and analyzed. | Can cause spontaneous abortion (rare). Detects abnormalities later in pregnancy than other tests but is very accurate. |
| *Many newer tests are experimental, soon to be offered to the general public. Therefore, this list is partial, to illustrate that many tests are used at various times during pregnancy to indicate possible problems. |