Accurate early ultrasounds dating pregnancy
An invasive method involves probes or needles being inserted into the uterus, e.g.
amniocentesis, which can be done from about 14 weeks gestation, and usually up to about 20 weeks, and chorionic villus sampling, which can be done earlier (between 9.5 and 12.5 weeks gestation) but which may be slightly more risky to the fetus.
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.
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.
Since screening tests yield a risk score which represents the chance that the baby has the birth defect, the most common threshold for high-risk is 0.ACOG guidelines currently recommend that all pregnant women, regardless of age, be offered invasive testing to obtain a definitive diagnosis of certain birth defects.Therefore, most physicians offer diagnostic testing to all their patients, with or without prior screening and let the patient decide.One study comparing transabdominal chorionic villus sampling with second trimester amniocentesis found no significant difference in the total pregnancy loss between the two procedures.However, transcervical chorionic villus sampling carries a significantly higher risk, compared with a second trimester amniocentesis, of total pregnancy loss (relative risk 1.40; 95% confidence interval 1.09 to 1.81) and spontaneous miscarriage (9.4% risk; relative risk 1.50; 95% confidence interval 1.07 to 2.11).