The importance of embryo quality and womb lining thickness in natural cycle IVF

This study looked at whether womb lining thickness and embryo quality affect the natural cycle during in vitro fertilization (NC-IVF). It found that thicker womb linings and better quality embryos were related to higher pregnancy rates.

IVF is an infertility treatment in which eggs (oocytes) are removed from a woman’s body and fertilized in the laboratory, and the embryos are implanted in her womb. Often, medications are used to stimulate the ovaries to develop multiple egg-containing follicles. Natural cycle IVF is an alternate treatment in which a single follicle develops under the body’s own hormones. Both types of IVF use a medication to trigger egg release.

Multiple factors affect the success of IVF. The thickness of the lining of the womb is related to the embryo’s ability to implant successfully. Embryo quality also affects success rates. Embryo quality can be determined by inspecting embryos under a microscope. Compared to traditional IVF, there are fewer studies showing how these factors affect natural cycle (NC) IVF.

This study used records from 552 NC-IVF embryo transfers. The women were under 38 years old and had normal body weights. 18.8% of patients had a positive urine pregnancy test. 17.03% of women became clinically pregnant (observable on ultrasound).

The pregnancy rate increased as the womb lining thickness increased until a thickness of 10 mm was reached. Only one patient with a womb lining less than 7 mm thick became pregnant, and that pregnancy ended in early miscarriage. Women who became pregnant had significantly thicker womb linings than those who did not (11.4 vs. 8.6 mm).

Top-quality embryos were the most likely to implant. Top-quality day-3 embryos had 8 cells with one nucleus a piece. They also have less than 10% fragmentation (abnormal small cell pieces). After adjusting for other factors, embryos with less than 10% fragmentation were 71% more likely to implant than embryos with more fragmentation.

This study found that top-quality embryos and thicker endometrial linings were related to higher pregnancy rates in NC-IVF.

Studies which use medical records (are retrospective) can have more bias than other studies.