Recurrent Miscarriage: Causes, Tests and Treatments That Work

What causes recurrent miscarriage

Chromosome errors in the pregnancy — the commonest cause

Around 50 to 60% of first-trimester miscarriages are due to embryonic aneuploidy. The rate rises steeply with maternal age: roughly 50% of tested miscarriages in women under 35, and 75% in women over 40.

These are almost always sporadic random events. They are not inherited, not caused by anything you did, and they do not recur because of something either parent carries.

A counter-intuitive point that matters

Compared with women who have had an isolated miscarriage, women with recurrent loss have a higher likelihood of euploid miscarriage — losses where the chromosomes were normal — and that likelihood increases with the number of losses.

So repeated loss tends to select for losses that are not explained by chromosome errors. This is precisely why testing the miscarriage tissue is informative rather than merely confirmatory, and why ASRM now recommends it as the first step.

Uterine factors

Congenital uterine anomalies are found more often in women with recurrent loss than in the general population — around 13.3% versus 5.5%. Septate and bicornuate uteri are associated with increased miscarriage risk.

Acquired factors include endometrial polyps, submucosal fibroids and intrauterine adhesions. ASRM notes recurrent loss is itself a risk factor for developing adhesions, which can follow uterine instrumentation including curettage.

Surgical correction of a septum and of acquired defects may be offered, though ASRM classes these as treatments of possible benefit with limited or conflicting evidence.

Antiphospholipid syndrome

An acquired thrombophilia, genuinely associated with recurrent loss, and treatable. Diagnosis requires persistent antibodies on two occasions at least 12 weeks apart, alongside clinical criteria.

This is the one thrombophilia worth testing for — and it is routinely confused with inherited thrombophilias, which are not associated with recurrent loss and should not be tested for.

Thyroid

Overt hypothyroidism is associated with increased miscarriage risk and should be treated. Subclinical hypothyroidism with RPL should be treated where TSH is above 4 mIU/L.

Thyroid antibody screening is not recommended — large randomised trials found no benefit from treating euthyroid women with thyroid autoimmunity.

Parental chromosome rearrangements

A balanced translocation in one partner accounts for a small percentage of couples. Where found, outcomes are better than couples expect: observational studies report live birth rates of 70 to 71% without any assisted reproduction.

Male factors

Advanced paternal age and metabolic health are associated with miscarriage. Standard semen parameters do not appear predictive, but elevated sperm DNA fragmentation is associated with miscarriage.

Chronic endometritis

Previously thought worth treating. ASRM (2026) now reports a high-quality randomised trial in which 438 women with RPL and biopsy-confirmed chronic endometritis received doxycycline or placebo, showing no significant difference in miscarriage or live birth.

Unexplained

The most common outcome of a complete evaluation — and the prognosis remains good. 50 to 80% succeed in a subsequent pregnancy without specific treatment.