In vitro fertilisation is a treatment method that has been used worldwide for about 30 years. IVF success rates vary from 8.6 per cent to 46 per cent. This incredible difference in success rates depends on certain factors. The age of the expectant mother is the factor that affects IVF success rates the most. The good morphological quality of the embryo is one of the factors that positively affect success. The characteristics of the endometrium (uterine wall) is another important issue that affects success. The appearance (pattern) of the endometrium, blood flow under the endometrium (sub-endometrial flow) and endometrial thickness directly affect the success of pregnancy.
Endometrium thickness can be easily measured by transvaginal ultrasound. Thin endometrium means that the success rate of IVF is low. The definition of thin endometrium is not clear. There is no consensus on how many millimetres the ideal thickness should be. Despite the lack of consensus, measurement of endometrial thickness remains part of the standard follow-up during IVF treatment.
The most extensive review of the subject suggest that endometrial thickness has no direct effect on the ongoing pregnancy rates in IVF treatments. However, it has been shown that uterine wall thickness below 7 mm significantly decreases IVF success rates.
It is not clear why a thin uterine wall reduces pregnancy success. Unfortunately, there is lack of research on diagnostic tissue in people with thin uterine walls. Presumably, oxygen levels are increased in the lower layers of the thin endometrium. High oxygen levels impair the implantation of the embryo.
According to the results of the referenced review, an endometrium thickness of less than 7 mm was accepted as thin endometrium. However, a thickness of less than 10 mm decreases pregnancy rates.
