# Recurrent Pregnancy Loss: Genetic Evaluation

## Overview

Recurrent pregnancy loss (RPL) is defined as two or more clinically recognized pregnancy losses (ACOG) or three or more (ESHRE, WHO traditional definition), affecting approximately 1-2% of couples. Genetic factors are the most common identifiable cause, accounting for roughly 50-60% of first-trimester losses. Chromosomal abnormalities in the conceptus (embryonic/fetal aneuploidy) are the single most frequent etiology, and parental chromosomal rearrangements are found in 3-5% of couples with RPL.

## Chromosomal Causes of Pregnancy Loss

### Embryonic/Fetal Aneuploidy

Approximately 50-70% of first-trimester miscarriages are chromosomally abnormal. The most common aneuploidies in miscarriage include autosomal trisomies (trisomy 16 being most common, followed by trisomies 22, 21, 15, 13, and 18), monosomy X (accounting for roughly 20% of chromosomally abnormal miscarriages), triploidy (approximately 15%), and tetraploidy (approximately 5%). Aneuploidy frequency increases with maternal age, and recurrent aneuploidy in sequential losses is common, particularly in women over 35 years. Most embryonic aneuploidies are sporadic events resulting from random meiotic nondisjunction rather than inherited causes.

### Parental Chromosomal Rearrangements

Parental rearrangements are found in approximately 3-5% of couples with RPL, representing a ten-fold higher frequency than in the general population. Balanced reciprocal translocations are the most common structural rearrangement in RPL couples. The carrier is phenotypically normal, but meiotic segregation produces unbalanced gametes leading to miscarriage or abnormal offspring. Empiric risk for unbalanced live birth varies by translocation but generally ranges from 5-30%. Robertsonian translocations, most commonly rob(13;14) and rob(14;21), carry recurrence risks dependent on the chromosomes involved; rob(14;21) carries a trisomy 21 offspring risk of approximately 10-15% if the mother is the carrier and 1-3% if the father is. Pericentric inversions may produce unbalanced recombinant gametes, while paracentric inversions rarely cause unbalanced offspring.

<image>Diagram illustrating meiotic segregation patterns in a reciprocal translocation carrier, showing the possible gamete outcomes (normal, balanced carrier, unbalanced with partial trisomy/monosomy) and their clinical consequences</image>

| Genetic Finding | Frequency in RPL Couples | Clinical Significance | Management |
|---|---|---|---|
| Fetal aneuploidy (sporadic) | ~50–70% of individual losses | Most common cause; increases with maternal age | Reassurance; age-related counseling |
| Balanced reciprocal translocation | ~2–3% of couples | Unbalanced gametes → miscarriage or abnormal offspring | PGT-SR or natural conception + prenatal diagnosis |
| Robertsonian translocation | ~1–2% of couples | Risk depends on chromosomes involved | Parental karyotype; PGT-SR; prenatal diagnosis |
| Pericentric inversion | Rare | May produce unbalanced recombinant offspring | Case-specific risk assessment |
| X-linked lethal conditions | Rare | Recurrent male-only losses | Targeted testing if pattern suggests |
| Lethal single-gene disorders | Rare | Recurrent losses with specific fetal phenotype | POC exome sequencing; targeted testing |

## Products of Conception (POC) Analysis

### Indications

POC analysis is recommended after the second and subsequent losses to determine if the loss was chromosomally abnormal. It helps distinguish chromosomal (often sporadic) from non-chromosomal causes of loss and is particularly valuable in guiding further workup, since recurrent euploid losses warrant more extensive evaluation for non-genetic causes.

### Testing Methods

Conventional karyotype requires cell culture of POC tissue but has a 10-40% culture failure rate and risk of maternal cell contamination (MCC). Chromosomal microarray can be performed on uncultured tissue with a lower failure rate (approximately 5%) and detects CNVs, though it cannot detect triploidy or balanced rearrangements without additional analysis. SNP microarray can detect triploidy through patterns of loss of heterozygosity and identify MCC. Maternal cell contamination is a major confounder, with up to 20-30% of POC cultures potentially overgrown by maternal cells, producing a falsely "normal female" (46,XX) result.

### Interpreting Results

An aneuploid POC result explains the loss, supports a sporadic etiology, and may reassure the couple. A euploid POC result means the loss is not explained by aneuploidy and warrants further evaluation for anatomic, thrombophilic, immunologic, and endocrine causes. A 46,XX result may be the true fetal karyotype or may represent maternal cell contamination; microsatellite analysis or SNP array can help distinguish these. Recurrent euploid losses are more concerning for a persistent underlying cause.

## Parental Karyotype

### Indications

Parental karyotyping is recommended for all couples with RPL (ACOG, ASRM). It is particularly important when POC analysis reveals an unbalanced structural abnormality suggesting a parental balanced rearrangement. Both partners should be tested using peripheral blood lymphocytes.

### Findings and Counseling

Approximately 3-5% of couples will have a balanced rearrangement. When identified, counseling explains the mechanism of unbalanced gamete production, provides estimated risks for future pregnancy outcomes, and discusses reproductive options: natural conception with prenatal diagnosis, PGT-SR with IVF, donor gametes, or adoption. Genetic counseling for extended family members who may also be carriers is recommended. If karyotypes are normal, other causes of RPL should be investigated.

<image>Algorithm for the genetic evaluation of recurrent pregnancy loss, from initial parental karyotyping and POC analysis through tiered investigation including thrombophilia screening, uterine evaluation, and consideration of PGT-SR</image>

## Role of PGT-SR in Translocation Carriers

### Rationale

Translocation carriers have a high proportion of chromosomally unbalanced embryos. PGT-SR selects balanced/normal embryos for transfer, reducing miscarriage risk. Achievable pregnancy rates are approximately 40-60% per cycle in experienced centers.

### Considerations

PGT-SR cannot distinguish between normal and balanced carrier embryos without additional haplotyping. Prenatal diagnosis can confirm fetal karyotype and distinguish carrier status if desired. The cost and burden of IVF must be weighed against natural conception plus prenatal diagnosis. Some couples with balanced translocations may achieve successful pregnancies naturally depending on the specific rearrangement, and decision-making should be individualized based on reproductive history, maternal age, and couple preferences.

## Additional Genetic Considerations in RPL

### Single-Gene Disorders

Rare but recognized causes of RPL include lethal skeletal dysplasias (recessive conditions causing recurrent second-trimester losses with skeletal abnormalities), lethal metabolic disorders causing recurrent fetal demise, and X-linked lethal conditions presenting as recurrent male-only losses (such as incontinentia pigmenti, IKBKG). Exome/genome sequencing of POC tissue is emerging as a research tool for unexplained recurrent euploid losses.

### Thrombophilia Genes

Factor V Leiden and prothrombin G20210A have been associated with RPL, primarily late losses. Their role in early RPL is debated. Antiphospholipid antibody syndrome is the most important acquired thrombophilic cause of RPL.

### Parental Age Effects

Advanced maternal age increases aneuploidy risk due to meiotic nondisjunction. Advanced paternal age is associated with increased de novo mutations, but its contribution to RPL is less well-established. Sperm aneuploidy rates are elevated in male partners of RPL couples in some studies.

## Non-Genetic Causes (Brief Overview for Context)

Non-genetic causes include uterine anomalies (septate uterus being the most common correctable cause), antiphospholipid syndrome (treated with aspirin plus heparin), endocrine factors (thyroid disease, uncontrolled diabetes, PCOS), and lifestyle factors (smoking, alcohol, obesity). Approximately 50% of RPL remains unexplained after comprehensive evaluation, though the prognosis for future pregnancy is generally favorable at 60-70% live birth rate.

<image>Pie chart showing the distribution of etiologies in recurrent pregnancy loss: chromosomal abnormalities, parental rearrangements, uterine anomalies, antiphospholipid syndrome, endocrine factors, and unexplained causes with approximate percentages</image>

## Clinical Pearls

The most common cause of any single miscarriage is fetal aneuploidy, and the most common finding in RPL couples is recurrent fetal aneuploidy, especially with advancing maternal age. Parental karyotyping should be offered to all couples with RPL -- a 3-5% detection rate for balanced rearrangements significantly impacts management and recurrence risk counseling. A "normal female" (46,XX) POC result should be interpreted with caution due to the high rate of maternal cell contamination in culture-based methods; SNP array is preferred to detect MCC. Recurrent euploid losses warrant more aggressive investigation for non-chromosomal causes (anatomic, thrombophilic, immunologic). PGT-SR is beneficial for translocation carriers but adds cost and IVF burden; natural conception with prenatal diagnosis is a reasonable alternative depending on the specific translocation and reproductive history. The prognosis for couples with unexplained RPL is generally good, with approximately 60-70% achieving a successful pregnancy with supportive care alone. Extended family members of balanced translocation carriers should be offered carrier testing and genetic counseling.

## References

- Practice Committee of the ASRM. "Evaluation and treatment of recurrent pregnancy loss: a committee opinion." *Fertility and Sterility*. 2012;98(5):1103-1111.
- ESHRE Guideline Group on RPL. "ESHRE guideline: recurrent pregnancy loss." *Human Reproduction Open*. 2018;2018(2):hoy004.
- Stephenson MD, Sierra S. "Reproductive outcomes in recurrent pregnancy loss associated with a parental carrier of a structural chromosome rearrangement." *Human Reproduction*. 2006;21(4):1076-1082.
- Sahoo T, Dzidic N, Engel MH, et al. "Comprehensive genetic analysis of pregnancy loss by chromosomal microarrays: outcomes, benefits, and challenges." *Genetics in Medicine*. 2017;19(1):83-89.
- Franssen MT, Korevaar JC, van der Veen F, et al. "Reproductive outcome after chromosome analysis in couples with two or more miscarriages." *BMJ*. 2006;332(7544):759-763.