Blood tests during a pregnancy have two purposes that will be covered here for all you new dads-to-be. Some prenatal screening tests are for your partner's overall well-being and check for potentially harmful medical conditions. Second-trimester quadruple-screen blood tests are aimed at determining the risk of genetic anomalies in the fetus.
Also used in conjunction with second-trimester ultrasound, quadruple screens help predict the risk that the fetus has Down syndrome, trisomy 18, or neural tube defects such as spina bifida or anencephaly, where part of the brain is missing.
Quadruple screens test the blood for four things:
Alpha feto-protein, produced by the fetus: High levels of AFP may indicate neural tube defects, abdominal wall defects, or a multiple pregnancy.
Estriol, a form of estrogen made by the placenta and liver of the fetus: Estriol levels are low in Down syndrome pregnancies.
hCG, produced by the placenta: hCG levels may be higher than normal in Down syndrome pregnancies.
Inhibin A, produced by the placenta: Inhibin A levels are elevated in cases of Down syndrome.
Newer blood tests that extract DNA from mom's blood rather than from the placenta or from amniotic fluid — both procedures that carry considerably more risk — can assess your risk for having a baby with trisomy 13, 18, or 21 and can also test for baby's sex.
These tests are expensive and not routinely offered; insurance may cover the cost if your partner has risk factors, such as being over 35 or having a previously affected child. Talk to your medical practitioner about the benefits of these blood tests, which can be done as early as the 11th week of pregnancy.
They're more than 90 percent successful in detecting these chromosomal abnormalities but also have about a 5 percent false positive rate.
In the second trimester, amniocentesis may be done between weeks 15 and 20, when amniotic fluid is easily accessible. A thin needle is inserted into the fluid through the abdominal wall, and the fetal cells in the fluid are analyzed.
Amniocentesis comes with a slightly increased risk of miscarriage afterward, so most medical practitioners don't recommend doing an amniocentesis routinely. Women older than 35, who have a higher risk of having a child with chromosomal abnormalities, and those with a family history of genetic problems may consider doing amniocentesis, which can determine whether chromosomal defects such as Down syndrome, hemophilia, cystic fibrosis, and other genetic disorders are present.