A stillbirth occurs when a fetus dies in the womb after 20 weeks of gestation or prior to delivery. In the United States, stillbirth occurs in 1 of every 160 births.
When pregnancy ends in stillbirth, health care providers may examine the baby's chromosomes with a technique known as a karyotype to attempt to determine a cause. The karyotype is an image of an individual's chromosomes and is used to look for an abnormal numbers of chromosomes or for abnormally shaped chromosomes. However, karyotyping requires cells to be grown in culture, which is often not possible in a stillbirth. Moreover, karyotyping does not always yield an explanation for the stillbirth.
Scientists supported by the Pregnancy and Perinatology Branch compared the results of karyotypes from more than 500 stillbirths to results from microarray analysis, a genetic method that detects small segments of missing parts of chromosomes (deletions) or additional sections of genetic material (duplications) that cannot be seen by karyotype. The researchers analyzed samples from all stillbirths in a population-based study in 5 areas, covered by 59 hospitals over a period of 2.5 years. Shortly after each stillbirth, parents gave research staff permission to collect blood from the umbilical cord and tissue from the fetus and the placenta.
Researchers obtained results from 70% of the karyotype tests that were performed, with 30% failing to yield any results. By comparison, microarray analysis provided results in 87% of stillbirths tested, a significantly higher yield than that of karyotyping. In addition, microarray analysis detected genetic abnormalities in a number of cases in which the karyotype analysis returned no result or a normal result. The scientists noted that, in some cases, the microarray analysis revealed genetic abnormalities carried by the parents. These genetic abnormalities had no apparent effect on the parents' health but could potentially increase the risk for another stillbirth or for certain health conditions in future offspring.
Knowledge of these genetic abnormalities would allow for improved management of future pregnancies (PMID: 23215556).