Chromosomal Abnormalities and Pregnancy Complications: What Every Parent Should Know

In short: Chromosome abnormalities are responsible for most early miscarriages and can cause birth defects such as Down syndrome, slow growth of the baby, death in the womb and molar pregnancy. They are screened for by the nuchal translucency scan, tests on the mother’s blood and cell-free fetal DNA testing, and diagnosed by chorionic villus sampling or amniocentesis. The risk can be reduced by IVF with genetic testing of the embryos.

Chromosomal abnormalities mainly affect early fetal development, placental function, and the structural integrity of the baby’s body systems.

That’s why chromosomal abnormalities can lead to problems with fetal growth and, in some cases, congenital anomalies.

The most common presentation of chromosomal abnormalities in early pregnancy is pregnancy loss (miscarriage). Understanding how these abnormalities happen can help you feel more informed and prepared if you or a loved one faces this situation.

• Early pregnancy loss:
• Errors of chromosomal distribution during cell division can lead to an abnormal number of chromosomes.
• Affected embryos often become non-viable.
• About half (50–60%) of early pregnancy losses are due to abnormal chromosomes.
• The most common are: trisomy 16 and Turner syndrome.
• Recurrent miscarriage:
• Chromosomal rearrangements in parental chromosomes can lead to repeated pregnancy loss.
• Birth defects:
• Down syndrome (errors in chromosome 21): heart defects and intellectual disability
• Edwards syndrome (errors in chromosome 18): severe developmental delay and high neonatal mortality
• Patau syndrome (errors in chromosome 13): brain and facial abnormalities
• Usually, chromosomal abnormalities present with congenital anomalies affecting multiple organ systems.
• Restriction of fetal growth:
• Chromosomal abnormalities can impair placental function.
• This may lead to restricted fetal growth with poorer outcomes.
• Intrauterine fetal death:

Chromosomally abnormal fetuses are more prone to passing away inside the womb.

• Placental abnormalities:
• Poor implantation and preeclampsia can sometimes be caused by chromosomal abnormalities.
• Molar pregnancy results from abnormal chromosomal fertilization, leading to abnormal placental tissue growth instead of a viable fetus.
• Infertility:
• Embryos with abnormal chromosomes often fail to implant or are lost before a woman even knows she is pregnant. Some chromosomal conditions in the parents (such as Turner syndrome in women, or Klinefelter syndrome and Y-chromosome microdeletions in men) can also cause infertility.

How can chromosomal abnormalities be screened for?

• Measuring nuchal translucency in the first trimester
• Blood biochemical markers
• Cell-free fetal DNA testing
• Combining these methods with each other and with maternal age for a more complete picture

How are chromosomal abnormalities diagnosed in pregnancy?

• Chorionic villus sampling: taking a placental sample and culturing it in the laboratory to study the fetal cells’ chromosomes
• Amniocentesis: taking a sample from the amniotic fluid and culturing it in the laboratory to study the fetal cells’ chromosomes
• Karyotyping/genetic testing of the products of conception after a miscarriage or pregnancy termination

Is there a way to reduce the chance of a pregnancy with chromosomally abnormal fetuses?

For couples with a known genetic condition or a chromosome rearrangement, IVF combined with genetic testing of embryos (PGT) before transfer can reduce this chance. Testing embryos for chromosome number (PGT-A) in other couples may lower the miscarriage rate per transfer in some groups, but it has not been shown to increase the overall chance of a baby, so it is decided case by case. However, this doesn’t guarantee a pregnancy free of complications such as miscarriage, congenital anomalies, or other issues mentioned above, since these can also occur due to causes unrelated to chromosomal abnormalities.

If you have concerns about recurrent miscarriage, family history of genetic conditions, or would like to learn more about screening and testing options, the team at Dr. Najeeb Layyous Clinic is here to guide you through your options with care and clear information.

Dr Najeeb Layyous F.R.C.O.G

Consultant Obstetrician, Gynecologist and Infertility Specialist