Risk of Miscarriage with Endometrial Polyp
Endometrial polyps appear to increase the risk of miscarriage, with evidence suggesting approximately a 27% miscarriage rate in women with polyps compared to 11% in those without polyps, though the data are limited and primarily from IVF populations. 1
Evidence for Increased Miscarriage Risk
The strongest direct evidence comes from a 1999 study examining IVF outcomes, which found:
Women with small endometrial polyps (<2 cm) who proceeded with embryo transfer without polypectomy had a miscarriage rate of 27.3% compared to 10.7% in the general IVF population (p=0.08, approaching statistical significance). 1
The pregnancy rate itself was not significantly reduced (22.4% vs 23.4%), suggesting polyps primarily affect pregnancy maintenance rather than implantation. 1
When polyps were removed hysteroscopically and embryos frozen for later transfer, the miscarriage rate normalized to 14.3%, similar to standard frozen embryo cycles (12.1%). 1
Supporting Evidence from Other Fertility Studies
Additional research reinforces the association between endometrial polyps and adverse pregnancy outcomes:
A 2012 study of women undergoing IUI demonstrated statistically significant improvement in cumulative pregnancy rates after hysteroscopic polypectomy compared to leaving polyps intact. 2
In a 2020 retrospective cohort of 204 infertile women with both endometriosis and endometrial polyps, 7 of 89 pregnancies (7.9%) ended in spontaneous abortion, though this study did not have a direct comparison group without polyps. 3
Clinical Context and Limitations
The evidence base is limited to infertility populations undergoing assisted reproduction, and no high-quality studies directly examine miscarriage risk in women conceiving naturally with endometrial polyps. 4, 5
Key limitations include:
- Most studies focus on pregnancy rates rather than miscarriage as a primary outcome. 4
- Polyp size, number, and location vary across studies, making direct comparisons difficult. 5
- Approximately 25% of polyps resolve spontaneously, particularly those <10 mm. 5
- The overall malignancy risk in polyps is low (approximately 3%), but increases with menopause and abnormal bleeding. 5
Proposed Mechanism
While the exact mechanism remains unclear, potential explanations include:
- Mechanical interference with implantation or placental development 4
- Local inflammatory changes in the endometrium 4
- Altered endometrial receptivity 4
Clinical Implications
For women with known endometrial polyps planning pregnancy, particularly those undergoing IVF, hysteroscopic polypectomy prior to embryo transfer appears to reduce miscarriage risk to baseline levels. 1
The decision becomes more nuanced for:
- Small polyps (<10 mm) in premenopausal women, which may regress spontaneously 4, 5
- Asymptomatic polyps discovered incidentally, where conservative management is reasonable 5
- Women with repeated IVF failure, where polypectomy is currently justified 4
Symptomatic polyps causing abnormal uterine bleeding should be removed regardless of pregnancy plans. 5