Endometrial Thickness: What’s Normal for Pregnancy?

There’s plenty of things going on in your body that you think you understand – until you realize you don’t. Especially if you’re hoping to get pregnant, researching the uterus and menstrual cycle probably reveals a lot of information you’ve either forgotten from health class in school, or just straight-up never heard of before. Let’s explore one of the most important topics for future moms: the endometrium, and why endometrial thickness is so important for fertility.

What is the endometrium?

woman belly uterus womb

The endometrium is a layer of mucous membranes lining the inside of the uterus. It consists of 2 layers: the functional layer, which comes unstuck and is shed during menstruation, and the basal layer, which is always retained.

The endometrium changes in accordance with your menstrual cycle. To prepare for a possible pregnancy, the functional layer thickens, which allows a fertilized egg to implant itself easily. However, if the egg is not fertilized, it breaks down and bleeds out, leaving the basal layer to begin generating a new functional layer in the next cycle.

What endometrial thickness is normal before and after ovulation?

length measure tape question

The endometrium is quite thin, in and of itself. Right after the end of your period, when the functional layer has bled out, the basal layer is only about 1 millimeter thick. The cells of the functional layer multiply as ovulation approaches, causing it to thicken.

The thickness of the functional layer varies between individuals, and there’s no “normal” thickness it needs to be. However, by ovulation, it is generally around 8 mm thick. As it continues to thicken in preparation for the implantation of a fertilized egg, it ends up around 15 mm thick.

If pregnancy needs a thickened endometrium, what if it’s too thin?

woman question

It’s still not exactly clear what the optimum thickness for pregnancy may be, or if there is one. However, if the endometrium in preparation for a fertilized egg doesn’t thicken beyond 6 mm, it’s usually judged to be too thin to support a pregnancy. Another research from Japan suggests that even at more than 8 mm thickness, women are less likely to fall pregnant if the overall rate of cell division in the endometrium is too low.

It’s not known why some women struggle with thin endometrium, but there are a few theories. One contributing factor could be a deficit in the action of the hormones estrogen and progesterone (both of which encourage endometrial cell division and thickening). Ironically, it’s also been posited that some fertility drugs designed to induce ovulation may have a side effect of thinning the endometrium.

Endometrial thickness: how much is too much?

balloon heart color

You might get the impression that when it comes to pregnancy, the thicker endometrium gets, the better. But, it’s also possible for the endometrium to be too thick. When this happens, it becomes known as a condition called endometrial hyperplasia. This is thought to be caused by an excess production of estrogen in most cases.

The endometrium is only a few millimeters thick, but it has a huge influence on whether or not you get pregnant. When you’re hoping to get pregnant, it can help to know a bit of what’s going on in your body, and what role different parts play. The more information you gather, the better prepared you’ll be!