Recurrent miscarriage or recurrent pregnancy loss (RPL) is the spontaneous loss of 2–3 pregnancies that is estimated to affect up to 5% of women. The exact number of pregnancy losses and gestational weeks used to define RPL differs among medical societies.
In the majority of cases, the exact cause of pregnancy loss is unexplained despite genetic testing and a thorough evaluation. When a cause for RPL is identified, almost half are attributed to a chromosomal abnormality (ie. aneuploidy). RPL has been associated with several risk factors including parental and genetic factors (ie. advanced maternal age, chromosomal abnormalities, sperm DNA fragmentation), congenital and acquired anatomical conditions, lifestyle factors (ie. cigarette smoking, caffeine, alcohol, stress), endocrine disorders, thrombophilia (clotting disorders), immunological factors, and infections. The American Society of Reproductive Medicine recommends a thorough evaluation after 2 consecutive pregnancy losses; however, this can differ from recommendations by other medical societies.
RPL evaluation can be evaluated by numerous tests and imaging studies depending on the risk factors. These range from cytogenetic studies, blood tests for clotting disorders, hormone levels, diabetes screening, thyroid function tests, sperm analysis, antibody testing, and imaging studies. Treatment is typically tailored to the relevant risk factors and test findings. RPL can have a significant impact on the psychological well-being of couples and has been associated with higher levels of depression, anxiety, and stress. Therefore, it is recommended that appropriate screening and management (ie. pharmacologic, counseling services) be considered by medical providers.
Epidemiology Pregnancy loss, also referred to as miscarriage or spontaneous abortion, occurs in up to 25% of pregnancies. Recurrent pregnancy loss occurs less frequently and it is estimated that 5% of women experience two consecutive pregnancy losses while only 1% experience three or more.
Etiology and risk factors
The cause of recurrent pregnancy loss is unknown in about 50% of cases. Risk factors that have been associated with RPL include parental and genetic factors (advanced maternal age, chromosomal abnormalities, sperm DNA fragmentation), anatomical conditions, lifestyle factors, endocrine disorders, thrombophila (bleeding disorders), immunological factors, and infections. Despite thorough evaluation for these risk factors, the exact cause for recurrent pregnancy loss is unknown in about 50% of cases.
Parental and genetic factors
Advanced maternal age: Maternal age is associated with increased risk of miscarriage with a rate of 50% in women over 40 years of age. This higher likelihood of pregnancy loss can be attributed to the higher incidence of trisomies, a chromosomal abnormality, seen in women over the age of 35. Chromosomal abnormalities: Recurrent pregnancy loss is most commonly found to be caused by chromosomal abnormalities in the fetus, accounting for approximately 50% of cases. These include structural aberrations (such as chromosomal inversions, insertions, deletions, and translocations) and numerical aberrations, also called aneuploidies (trisomies, monosomy X, and triploidy). These can be detected by cytogenetic testing such as karyotyping (test that analyzes the structure and quantity of chromosomes), FISH, MLPA, aCGH, and SNP array. Some research suggests that chromosomal abnormalities occur more frequently in sporadic pregnancy loss than in recurrent pregnancy loss, and the incidence of RPL is lower in women with 3 or more pregnancy losses. Parental chromosomal abnormalities is a rare cause of RPL, found in approximately 2-4% cases. Studies comparing pregnancy outcomes in couples experiencing RPL with and without chromosomal abnormalities found that parental carriers of chromosomal abnormalities had a lower live birth rate, specifically carriers of a reciprocal/balanced Robertsonian translocation. This evidence suggests that although RPL can occur in both couples with and without chromosomal aberrations, those that do are at higher risk of pregnancy loss. Previous studies produced conflicting results. Genetic evaluation of RPL is generally recommended in order to determine the need for genetic counseling and appropriate treatment. This, however, can differ among medical societies where others recommend against routine cytogenetic testing for couples experiencing RPL as it is of little clinical benefit. It is instead considered after individual risk assessment (ie. family history) and recommended to test parental chromosomes rather than the products of conception. Paternal Factors: There is emerging research that suggests male factors may contribute to recurrent pregnancy loss. A systematic review found that sperm DNA fragmentation, defined as breaks in the DNA strand of sperm cells, may be associated with RPL. Their findings included higher rates of SDF and other sperm parameters (ie. lower sperm number, motility, or ejaculation volume) in men experiencing RPL. No evidence of a relationship between RPL and paternal age, BMI, smoking, or alcohol use. The European Association of Urology Guidelines on Sexual and Reproductive Health therefore recommends SDF testing in cases of infertility or recurrent pregnancy loss.
Anatomical conditions Fifteen percent of women who have experienced three or more recurring miscarriages have some anatomical reason for the inability to complete the pregnancy. The structure of the uterus has an effect on the ability to carry a child to term. Anatomical differences are common and can be congenital or acquired.
Congenital: Congenital uterine malformations include unicornuate, septate, bicornate, didelphic, and arcuate uteri. The relationship between uterine abnormalities that are present from birth and RPL is unclear, however, there is an association with pregnancy loss. These structural anomalies are a result of disruption of the Müllerian tract during development. These can be found in approximately 12.6% of RPL cases with the highest incidences occurring in patients with septate (44.3%), bicornuate (36%), and arcuate (25.7%) uteri. These Structural uterine abnormalities can be visualized by several imaging studies including, hysterosalpingography, ultrasound, and MRI. Acquired: Other structural uterine anomalies such as uterine fibroids, polyps, and adhesions (also known as Asherman's syndrome) have a less clear association with recurrent pregnancy loss. Cervical weakness has been shown to lead to premature pregnancy loss resulting in miscarriages or preterm deliveries. It has been estimated that cervical insufficiency is a cause in about 8% of women with second trimester recurrent miscarriages.
Lifestyle factors
While lifestyle factors have been associated with increased risk for miscarriage in general, and are usually not listed as specific causes for RPL. These include cigarette smoking, caffeine intake, alcohol use, BMI, and stress.
Smoking: There is limited research that directly looks at the association of cigarette smoking and RPL. Recently, a systematic review that looked at studies evaluating the link between RPL and smoking was unable to find a significant difference in risk of recurrent pregnancy loss between people that smoke and non-smokers. This review did not address e-cigarettes and vaping given that the authors did not find any studies that looked into the relationship between these forms of smoking and RPL. The relationship between smoking and the risk of miscarriage has been extensively researched. According to a systematic review and meta-analysis, there is some evidence that active cigarette smoking increases the risk of miscarriage and this risk is further increased the more cigarettes that a person smokes a day. This same review highlights that according to the Surgeon General's report in 2010, research supports that smoking during pregnancy can also lead to pregnancy complications such as placental abruption, preterm delivery, and low birthweight among other maternal health risks. Caffeine: research regarding the association of caffeine intake and spontaneous pregnancy loss has produced inconsistent results in previous years due to the influence of multiple factors and limitations in data collection among the studies. The same systematic review that looked at the relationship between cigarette smoking and RPL in 2021 found that there was no increased risk of RPL with the consumption of caffeine. There have been more recent studies that have assessed the relationship between caffeine and miscarriage. A systematic review found that coffee consumption before and during pregnancy was associated with a higher risk of pregnancy loss. The risk of pregnancy loss increased by 3% with each additional cup of coffee consumed during pregnancy. There was also an increased risk of pregnancy loss of 14-26% with the consumption of an additional 100 mg of caffeine (coffee, tea, soda, cacao) per day during pregnancy. This increased risk was not seen if the caffeine products were consumed prior to pregnancy. The harmful effects of caffeine during pregnancy can be attributed to its ability to absorb rapidly into the bloodstream and cross into the placenta, along with the slowed breakdown of caffeine that occurs during pregnancy which can expose the fetus to caffeine and its metabolites for a prolonged period of time. Caffeine consumption can also lead to maternal cardiovascular effects that reduce placental blood flow, putting the development of the fetus at risk. Alcohol Use: Prenatal exposure to alcohol has been shown to have damaging effects on the cognitive development of the fetus and has been associated with low birthweight among other features of Fetal alcohol spectrum disorders due to its teratogenic effects. Similar to smoking and caffeine consumption, research studies assessing the relationship between alcohol use and pregnancy loss have produced inconsistent results. A systematic review that looked at several maternal lifestyle factors and the risk of recurrent pregnancy loss found no statistically significant increased risk in women that consumed any form of alcohol during pregnancy compared to those that did not. These findings are similar to a recent review that looked at alcohol intake in the first and second trimester and found no increased risk of miscarriage. The authors report that this may have been due to a limited number of studies included in the review, considering the exclusion of studies that did not differentiate trimesters or account for other external factors (such as smoking, maternal age, maternal BMI) that have been linked to pregnancy loss. There is evidence that in women that drink 5 or less alcoholic drinks per week, there is a 6% increased risk of miscarriage with each additional alcoholic drink consumed when the specific trimester is not specified. Due to the inability to determine a safe range of alcohol consumption during pregnancy, multiple medical societies recommend avoiding alcohol to prevent the potential harm to the fetus.