Prenatal diagnosis  deals with the early detection of chromosomal / genetic  abnormalities. Prior to a non-invasive or invasive examination of a genetic disease, patients/parents must be counseled. The genes are distributed in the cell nucleus of a total of 46 chromosomes, 23 of maternal and 23 of paternal origin, two chromosomes determine the sex of the child. In genetic tests during pregnancy, initially only the number of  chromosomes or larger microscopic visible structural defects of the chromosomes are detected; this examination is called karyotyping. In addition, it is now possible to detect even smaller structural defects of the chromosomes, up to single gene mutations of the DNA, by means of a microarray or sequencing (“Next Generation Sequencing”, NGS).

Not all methods are reimbursed by the health care system or  health insurances.

Invasive procedures

A genetic examination of the fetus is carried out by ultrasound-guided amniotic fluid sampling (amniocentesis), puncture of the placenta (chorionic villus sampling) or of the umbilical vein (fetal blood sampling). The cells obtained are examined in a genetic laboratory. The complications of invasive procedures  are rare (<1 %).

Non-invasive prenatal diagnosis in multiple  gestation

Meanwhile, it has  been possible to study chromosomal disorders or even the child’s blood group antigen in the circulating fetal DNA in maternal serum. This is called “non-invasive prenatal testing”. It only represents a risk assessment, which must be followed by invasive procedures if the results are suspicious. In twin gestation these tests can leads to good results in the exclusion of trisomy 21 and trisomy 18 of one or both children. For higher-order multiple pregnancies, non-invasive prenatal testing is currently not recommended.

Decision-making process

The most common reasons for an invasive examination are developmental disorders or malformations of one or both twins  on ultrasound. In early pregnancy, this can also be an enlarged nuchal translucency or, in twins, a significant size/weight discrepancy. In case of increased family risks, targeted genetic tests may be carried out.

The individual risk of a fetal trisomy can also be determined by a first-trimester ultrasound examination between 11+0 and 13+6 weeks of gestation,  which meanwhile may include  markers for chromosomal aberrations (such as nuchal translucency)  but also for other malformations such as spina bifida, cardiac or intestinal malformations.

When deciding for or against prenatal  diagnosis, the parents should be counselled about the consequences for all multiplets.

More information that is detailed can be found on our information leaflet.