When you choose IVF to help you conceive or overcome your fertility challenges, it is not just the number of eggs, sperm health, or quality that influences the outcome of the treatment. The uterus and its lining are also crucial factors in a successful pregnancy, even if it is through assistance. The endometrium thickness is very important for implantation and the outcome of an embryo transfer in IVF.
First, let’s understand what an endometrium is and why it is important for pregnancy.
The endometrium is the uterine lining that keeps changing throughout a woman’s menstrual cycle. The endometrium thickens when the uterus prepares for pregnancy. Around a woman’s ovulation time, the endometrium lining starts thickening in preparation for receiving a fertilised egg. When the uterus does not receive an embryo for implantation, the body realises there is no pregnancy and starts shedding this uterine lining. This shedding of the uterine lining is a woman’s menstrual period.
After menstruation, the endometrial lining is thin again. The entire process of thickening and shedding repeats every menstrual cycle until an embryo arrives. The functioning of this endometrium depends on two hormones – estrogen and progesterone. While estrogen contributes towards the formation of the endometrium, progesterone contributes towards the embryo implantation.
If the endometrial lining is too thin, embryo implantation may not be possible. A thick endometrium does not pose any risk or complications for a pregnancy. When the endometrial lining is neither too thick nor too thin, the chances of implantation are higher.
The endometrial lining can vary from woman to woman depending on various factors, including her age. Her menstrual cycle will also influence the thickness of the endometrium.
During a normal day, a woman of menstruating age will have an endometrial thickness of not more than 14 mm. The endometrial thickness is at its lowest during menstruation time. It can range between 2 mm to 4 mm and increase up to 7 mm right after menstruation. Before the ovulation stage (Days 11-14), the thickness will be around 11 mm. After ovulation, until the next menstruation period (Days 14 to 28), the endometrial thickness will be around 12 mm-13 mm.
For women who have attained menopause, the endometrial thickness will remain below 5 mm. For women on hormone therapy as a part of some medical fertility treatment, the endometrial thickness can reach up to 15 mm. If it exceeds 15 mm, a medical investigation is advisable to ensure everything is safe.
For a successful pregnancy, the endometrium should neither be too thin nor too thick. An endometrial thickness between 4 mm and 6 mm can also result in successful implantation and pregnancy, though below 7 mm thickness is considered to be too thin. An endometrial thickness between 8 mm and 15 mm can be ideal for natural conception.
One may not know about their endometrial thickness unless they undergo some fertility treatment or check-up that requires the measuring of their endometrium. So, the number of successful pregnancies, despite a very thin endometrium, is unknown.
One of the most important IVF success factors is the endometrial thickness at the time of embryo transfer. The ideal endometrial thickness required for a successful IVF is about 10 mm -14 mm. Less than 7 mm is considered too thin, and more than 14 mm is too thick.
With an endometrial thickness ranging between 10 mm and 14 mm, the live birth rate for a fresh embryo cycle is high. If the endometrium is less than 8 mm, the chances of successful implantation are low.
In IVF, the woman is usually given hormone injections to increase the number of mature eggs the follicles release. Such hormone injections can increase the thickness of the endometrium to go up to 15 mm.
The endometrial lining could be too thin due to the following reasons:
● Hormonal imbalance
● The advanced age of the woman
● Medical issues
● Inflammation
● Prior surgeries
● Insufficient nutrition
● Lack of blood flow
● Infections
● Stress
● Idiopathic
A thick endometrial lining of more than 14 mm is not safe either. It could indicate potential health issues that need to be looked into. Common causes for very thick endometrial lining are:
● Endometrium hyperplasia – The endometrial lining thickens and continues to grow due to the estrogen in the body, and the lack of sufficient progesterone prevents the body from shedding this lining.
● Anovulation – The absence of a menstrual period. The ovaries do not release a mature egg like they should every menstrual cycle. As a result, the body does not get the signal to produce progesterone. The lack of progesterone prevents the body from shedding the lining resulting in very heavy periods or bleeding between menstrual periods.
The endometrial lining is very important for pregnancy. Measuring the endometrial lining can provide the answers for many miscarriages and failed IVF cycles. The very thin or very thick endometrium can interfere with implantation and negatively impact the pregnancy outcome. Treatments like hormone supplements and medications can help bring the endometrial lining into the ideal range suitable for IVF embryo transfer and pregnancy.
● A very thin endometrial lining – less than 7 mm, can make it very difficult for the embryo to implant. After the embryo transfer on day 3 or day 5, the embryo will implant on the uterine wall. If the endometrial lining is not thick enough, it cannot hold the embryo. As a result, the embryo might detach from the uterine wall, resulting in a miscarriage.
● In an IVF treatment, the endometrial thickness is measured routinely to understand the endometrial receptivity of the embryo. The healthcare professional will measure the endometrial thickness with the help of transvaginal ultrasound and express the measurement in millimetres.
● An endometrial lining or endometrium could be thin due to inflammatory causes, medical conditions, prior surgeries, hormonal imbalances, abnormalities in the uterus, insufficient blood flow, or lack of nutrition. Sometimes it can be difficult to identify the exact cause.
