Testing in fetal death or stillbirth
Chromosomal microarrays have also replaced karyotypes as the recommended diagnostic test in evaluating tissue from a fetal demise. In addition to greater sensitivity, chromosomal microarrays do not require cultured cells. This has long been a major problem in studying miscarriages, as witnessed by a disproportionate number of 46, XX results, a reflection of unwitting laboratory analysis of maternal cells. It is difficult to avoid maternal admixture (decidua) in cultures of products of conception. With chromosomal microarrays, however, DNA alone from identifiable fetal tissue (villi) will suffice to generate results, without need for cell culture; thus, the percentage of informative cases has greatly increased (90%).
ACOG recommends that if only a karyotype were possible, cell culture should be initiated from amniotic fluid obtained by amniocentesis. This should maximize the rate of successful cell culture required for a karyotype.
Prenatal diagnosis procedures in maternal infection
Practice Bulletin 162 appropriately counsels that transmission of chronic maternal infection to the fetus is increased if an invasive procedure is performed in a mother who has hepatitis B, hepatitis C, or human immunodeficiency virus (HIV). However, risks can be mitigated. The once prohibitively high rate of maternal to fetal transmission in HIV is now greatly decreased when affected women receive combination antiretroviral therapy. In the study on which Practice Bulletin 162 recommendation was based, 30 of 2528 fetuses (~1% of ART-treated HIV) women were infected.8 Notwithstanding this 1%, Practice Bulletin 162 states that the risk of “newborn infection is not increased after amniocenteses, maternal viral load is low or undetectable.” A recommendation is made, however, to perform the necessary invasive procedure once viral loads are undetectable.
Practice Bulletin 162 states that loss rates following an invasive prenatal diagnostic procedure should now be communicated to be 1 in 769 for amniocentesis and 1 in 455 for CVS. For most practitioners, these new numbers will be more in sync with their clinical impressions. Also transformative in Practice Bulletin 162 is that chromosomal microarrays and not a karyotype should be ordered whenever an invasive prenatal procedure (CVS, amniocenteses) is performed. This holds whether evaluation is for a miscarriage or stillbirth.
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