Every woman who has been pregnant understands that in early pregnancy, the fear of pregnancy loss is very real. It’s the reason couples wait to tell family, friends, and coworkers. It’s why every ache, pain, or weird feeling is researched to see if it’s “normal”. The end of those first 12 weeks of pregnancy can’t come soon enough.
The truth is that 1 in 5 pregnancies will end in pregnancy loss and more than 50% of those are due to chromosomal abnormalities.
How Chromosomes Play a Role
Chromosomes are the genetic material inside the nucleus of each cell in the body. There are typically 46 chromosomes in a human cell, which match up like puzzle pieces to form 2 pairs of 23. One pair is inherited from the mother and the other from the father.
Sometimes though, the pairing-up of chromosomes isn’t always smooth. Structural abnormalities can be inherited or “de novo” (new to the individual) and occur as follows:
Monosomy-one of the chromosomes in a pair is fully or partially deleted. Turner Syndrome is an example of monosomy.
Trisomy– full or partial duplication of one of the chromosomes in a pair, creating an excess of genetic material. Down Syndrome is an example of trisomy.
Translocation– whole or part of one chromosome breaks off and is transferred to another chromosome. This can result in reciprocal translocation, in which two chromosomes exchange broken parts, or Robertsonian translocation, in which a full chromosome attaches to another complete pair. About 1 in 500 people will have a translocation.
In an unbalanced translocation, there is too much or too little genetic material. This may result in either pregnancy loss or developmental disabilities in the child.
In a reciprocal, or balanced, translocation there is no extra or missing genetic material. There are typically no outward signs of a balanced translocation.
People with a balanced translocation are considered carriers and may pass the translocation to their children. Balanced translocation carriers may have children with an unbalanced translocation if the inherited chromosome has too much or too little genetic material.
Inversion– part of the chromosome breaks off, inverts, and reattaches.
Rings– part of a chromosome breaks off and forms a ring.
If you suspect chromosomal abnormalities in yourself or your partner, or you have suffered multiple miscarriages, you should consider genetic testing. You may also elect to undergo IVF so that Preimplantation Genetic Testing for Aneuploidy (abnormal number of chromosomes) (PGT-A) can be done on embryos to check that they are chromosomally normal before they are transferred into the uterus.
Dr. Taraneh Gharib Nazem is Senior Fellow in Reproductive Endocrinology and Infertility at the Icahn School of Medicine at Mount Sinai/Reproductive Medicine Associates of New York. She is a board-certified Obstetrician Gynecologist. Dr. Nazem completed her residency in Obstetrics and Gynecology at the New York University School of Medicine, where she was elected administrative chief resident and graduated with the Robert F. Porges Honor Resident Award, for outstanding performance.