Pregnancy lost, or miscarriage, is a common complication in early pregnancy. Up to one in five women experience a miscarriage at some point in her life.
By definition, recurrent miscarriage refers to the loss of two or more pregnancies. Approximately 15 % of pregnancies end in miscarriage before the ninth week of pregnancy. Recurrent miscarriage is less common and affects approximately 1-2 % of couples. In these cases, each miscarriage increases the likelihood of recurrence in subsequent pregnancies, as it indicates that there is a common cause.
Despite this, the probability of a successful subsequent pregnancy remains good, at approximately 60-80%. Even a single miscarriage can cause significant emotional distress for woman and her partner, and recurrent miscarriage may increase feelings of despair.
Although in the majority of cases the cause of recurrent miscarriage remains unknown, investigations can provide information about the prognosis of future pregnancies and may help improve the changes of a successful outcome.
Chromosomal abnormalities in the embryo are the most common cause of recurrent miscarriages, accounting for 50-60 % of cases. This percentage increases with the woman’s age. These abnormalities can occur during embryo formation and be inherited from either parent.
The majority of miscarriages are caused by abnormalities in the number of chromosomes in the embryo. This happens when the sperm and/or egg does not contain the correct chromosomal number. The likelihood of chromosomal abnormalities increases with maternal age. In women in their 40s, 78% of embryos are chromosomally abnormal.
Women are born with all the egg cells they will ever have, and these eggs age over time along with the body. As age increases, so does the chance that chromosomes in the egg may not divide correctly during fertilization. This can lead to aneuploidy, where the embryo has an abnormal number of chromosomes (either too many or too few). Down syndrome is one example of this.
The risk of miscarriage increases with age:
The chromosomes of the fetus may be abnormal even if the parents’ chromosomes are normal. However, a chromosomal abnormality in one parent increases the risk of chromosomal abnormalities in the fetus.
Approximately 4% of couples with recurrent miscarriages have a chromosomal abnormality in the karyotype of one of the parents. Chromosomal abnormalities often involve missing or extra pieces of chromosomes. In the parent carrying the abnormality, the chromosomes are usually balanced, meaning the individual is healthy. However, the abnormality may be transmitted to the embryo in an unbalanced form, which can lead to miscarriage.
Parental karyotyping
A karyotype is analysed using a blood test that examines the size, shape and number of chromosomes (46 in total, organized in 23 pairs) within cells to identify major genetic abnormalities. A normal result shows 22 pairs of autosomes and two sex chromosomes (XX or XY).
Testing is recommended for both parents. This examination helps estimate the risk of future miscarriages, although it does not necessarily identify the exact cause of a miscarriage that has already occurred.
Fetal karyotyping
In the case of a miscarriage, it is also possible to determine a potential genetic cause.
To investigate the cause of a recently diagnosed miscarriage, fetal karyotyping can be performed. If testing reveals a genetic abnormality in the fetus, this may explain the cause of that particular miscarriage, although it does not necessarily explain earlier miscarriages.
A blood test from the patient can allow the determination of the karyotype of the non-developing embryo. Once implantation occurs, embryonic DNA can be detected in the mother’s blood, allowing analysis to be carried out after a miscarriage, even with only short delay.
The recommended treatment for recurrent miscarriages caused by genetic alterations is In Vitro Fertilisation with Genetic Analysis of the Embryos (PGT). In this approach, only chromosomally healthy embryos are transferred to the mother’s uterus.
High sperm DNA fragmentation is strongly associated with recurrent miscarriage. It often causes early miscarriage due to the embryo’s inability to repair paternal DNA damage. While traditional semen test may appear normal, high levels of DNA fragmentation can negatively affect embryo development.
Oxidative stress, smoking, obesity, varicocele and advance paternal age are key factors that increase DNA damage.
Laboratory testing analyses sperm using specialized assays to determine the percentage of fragmented DNA, known as the DNA Fragmentation Index (DFI).
Key actions include:
Miscarriage (early pregnancy loss) is common, occurring in about 10% of clinically recognized pregnancies. The most frequent cause is chromosomal abnormalities in the embryo, which usually happen by chance during fertilisation and early development.
Yes. The chance of miscarriage increases with age, mainly because the likelihood of chromosomal errors rises.
In most cases, yes. A miscarriage does not mean you cannot conceive again. Many miscarriages are sporadic events related to chance chromosomal changes, and most people go on to have a successful pregnancy.
