Two Losses. Three Losses. When Does a Miscarriage Become a Pattern — and What Does Modern Medicine Actually Know About Recurrent Pregnancy Loss?

The medical definition of recurrent pregnancy loss is three or more consecutive pregnancy losses before 20 weeks. Some specialist centres now investigate after two consecutive losses, recognising that the emotional toll is enormous and that in many cases an underlying cause will be found and treated. Recurrent pregnancy loss affects approximately one to two percent of couples trying to conceive, far more common than most people realise, yet still among the most isolating experiences in reproductive health, because each loss is private, often early, and invisible to the world around the couple. The silence is compounded by a medical culture that still sometimes treats repeated first-trimester loss as something women simply have to accept rather than something that warrants thorough investigation.

Chromosomal causes: the most common, the least preventable

Chromosomal abnormalities are the most common cause of individual early miscarriages, accounting for approximately 50-60% of losses. In most of these cases, the chromosomal error arises de novo in the embryo and is not indicative of any underlying problem in either parent. However, in a small percentage of cases, approximately 3-5% of couples with recurrent pregnancy loss, one partner carries a balanced chromosomal translocation that is structurally neutral in the carrier but produces unbalanced chromosomes in embryos. Both partners should have a standard karyotype (chromosome analysis) as part of the recurrent pregnancy loss workup. If a translocation is identified, preimplantation genetic testing through IVF can screen embryos before transfer.

Antiphospholipid syndrome: the most important treatable cause

Antiphospholipid syndrome (APS) is an autoimmune condition in which the body produces antibodies that increase blood clotting and interfere with placentation, causing early and late pregnancy loss. It is found in approximately 15% of women with recurrent pregnancy loss and is one of the most important diagnoses to identify because it is treatable. Treatment with low-dose aspirin and low-molecular-weight heparin (LMWH) injections during pregnancy significantly improves live birth rates in women with APS and recurrent pregnancy loss. APS requires specific blood tests, lupus anticoagulant, anticardiolipin antibodies, and anti-beta2-glycoprotein I antibodies, that are not part of a standard blood panel and must be ordered specifically, ideally on two occasions twelve weeks apart for a definitive diagnosis.

Uterine anatomical causes

Uterine anatomical abnormalities account for approximately 10-15% of recurrent pregnancy loss cases. The most common and most correctable is the uterine septum, a band of fibrous tissue that divides the uterine cavity and is associated with significantly elevated miscarriage rates due to poor blood supply at the implantation site. It is surgically correctable with hysteroscopic septum resection, and correction is associated with significantly improved pregnancy outcomes. Standard two-dimensional ultrasound frequently misses a uterine septum. Three-dimensional ultrasound or saline infusion sonography is more reliable. If you have had two or more miscarriages and have not had a three-dimensional uterine assessment, ask for one specifically.

Thyroid, progesterone, and other treatable factors

Thyroid dysfunction, particularly subclinical hypothyroidism with TSH levels between 2.5 and 4.5, is associated with increased miscarriage risk and is treated with levothyroxine supplementation. Current guidance recommends maintaining TSH below 2.5 in women with recurrent pregnancy loss who are attempting to conceive. Progesterone supplementation in the luteal phase and early pregnancy is now recommended by RCOG and supported by the PRISM trial evidence, which showed a modest but real reduction in pregnancy loss in women with vaginal bleeding in early pregnancy and a history of miscarriage. These are accessible, low-cost interventions with a reasonable evidence base and minimal risk.