The uterus is a made up multiple layers of smooth muscle that surround a lining (endometrial lining) where the embryo normally implants. The lower portion of the uterus is called the cervix which is usually several centimeters long and it serves as the entry point for sperm in natural intercourse. The cervix is the part of the uterus that dilates during labor to facilitate deliver of the baby.
The uterine muscle layer can have a single muscle cell that grows much faster and without regulation and develops into a ball of cells called a fibroid or myoma. If a myoma is very close to or pushing on the endometrial lining it can prevent normal implantation. Fortunately most myomas do not have any affect on getting pregnant or carrying a pregnancy to full term.
The endometrial lining can have some of its cells grow faster than the surrounding lining cells and produce an endometrial polyp. Small polyps are unlikely to affect the implantation of the embryo, whereas larger polyps located in the upper part of the uterine lining could have a significant affect on an embryo’s ability to implant.
Both polyps and myomas can be seen on an ultrasound, especially if sterile saline is infused as a contrast media. This procedure is called a saline sonogram or a sonohysterogram and is performed on all patients prior to an IVF cycle.
If there are no structural abnormalities like polyps or myomas in the endometrial lining and the lining can develop to a normal thickness of 8 mm or more; it is highly unlikely that the uterine lining will prevent a genetically healthy embryo from implanting.
Endometriosis has been implicated as a possible cause for implantation problems. Endometriosis can affect the function of the fallopian tube and create other problems in the pelvis, but there is much less evidence that endometriosis will be a problem inside the uterus. Remember, endometriosis is the uterine lining located outside of the normal area, not uterine lining in the normal area.
The genetically perfect embryo should be able to implant into the healthy endometrial lining without a problem.