Endometriosis and miscarriage – an overview of current evidence

Tommy's guest blog by Dr. Prathiba M. De Silva, 29/09/2017 

Endometriosis is diagnosed when the tissue lining the womb (endometrium) is found located outside it.

Approximately 1.5 million women in the UK live with this condition.¹ It is associated with chronic pelvic pain, difficulties in conceiving pregnancy, painful periods (dysmenorrhoea), painful sexual intercourse (dyspareunia), pain on opening bowels (dyschesia) and pain when urinating (dysuria), and can therefore have a significant impact on a woman’s quality of life.

Endometriosis causes scar tissue (adhesions) to distort the way in which the uterus, fallopian tubes and ovaries sit in the pelvis. Endometriosis around the ovary and tubes can prevent the egg from being released and meeting the sperm. Damage to the tubes from endometriosis can also cause the fertilised egg to implant in the tube to cause an ectopic pregnancy. Endometriosis is an inflammatory disorder associated with an abnormal immune response and also the production of toxins in the pelvis, both of which can contribute to difficulty in conceiving pregnancy.

What is not particularly clear is the effect of endometriosis on miscarriage after natural conception. Studies first looking at the link between reproductive outcome and endometriosis were first done in the 1980s. However, these were small poorly-designed studies, thus not providing truly reliable data. Such studies had conflicting outcomes, with some showing that treatment for endometriosis reduces miscarriage rates and others showing no benefit in treatment.

Randomized controlled trials (RCTs) offer the highest level of evidence available. To date, there are only two that have investigated endometriosis and miscarriage.  Both of these trials studied the effect of key-hole surgical treatment of mild endometriosis on miscarriage, comparing them to a control group of women who did not receive surgical treatment. When the results of these two trials (Marcoux, 1997 and Gad, 2012) were pooled together, there was no  significant reduction in the miscarriage rates between the pooled treated (70 patients) and non-treated (42 patients) group, suggesting that the treatment of endometriosis has no impact on miscarriage.²

There are, however, two large databases  that suggest that treatment of endometriosis can reduce miscarriage. The first is from a Swedish database collected from 1977-2009, encompassing 24667 women with endometriosis, and 98668 women without endometriosis.³ They found that women with endometriosis were 20% more likely to miscarry compared to women that did not. The second database is based in Scotland and comprises data collected from 1981-2010. The Scottish database compared 5375 women with endometriosis and 8710 women without endometriosis.⁴  They found that women with endometriosis are at higher risk of miscarrying compared to those without .

In summary, whilst the randomized controlled trials showed that the treatment of endometriosis had no impact on miscarriage rates, the large population-based databases showed a significant association between the two. It is impossible to make a  conclusion on whether endometriosis leads to miscarriages or not.

There is therefore a great need for higher quality research in order to help us establish whether endometriosis truly has a part to play in miscarriage.

 References: 

1. Endometriosis UK
2. Duffy JMN, Arambage K, Correa FJS, Olive D, Farquhar C, Garry R, Barlow DH, Jacobson TZ. Laparoscopic surgery for endometriosis. Cochrane Database of Systematic Reviews 2014, Issue 4. Art. No.: CD011031. DOI: 10.1002/14651858.CD011031.pub2.
3. Hjordt Hansen MV, Dalsgaard T, Hartwell D, Skovlund CW, Lidegaard Ø. Reproductive prognosis in endometriosis. A national cohort study. Acta Obstet Gynecol Scand 2014; 93:483–489.
4. Saraswat L, Ayansina DT, Cooper KG, Bhattacharya S, Miligkos D, Horne AW, Bhattacharya S. Pregnancy outcomes in women with endometriosis: a national record linkage study. BJOG 2017;124:444–452.