During the first half of a menstrual cycle, the uterus’ endometrium grows a layer of tissue and mucus that forms an ideal place for an embryo to implant. A healthy uterine lining (a.k.a. the endometrial lining) with good blood supply also allows the placenta to grow, which is how the baby receives nourishment and oxygen during pregnancy. However, if the uterine lining is too thin, it may lower your chances of a successful pregnancy (1). To give yourself the best chance of implantation during your in vitro fertilization (IVF) cycle, here are some tips for optimizing your uterine lining before embryo transfer.
How well the uterine lining grows depends on a healthy balance of the hormones estrogen and progesterone throughout your menstrual cycle (2). As estrogen levels rise during the first half of your menstrual cycle, the uterine lining grows, too. After your ovary releases an egg, your body begins to produce much less estrogen and more progesterone. This change in hormones stops the growth of the uterine lining, causes it to mature, and prepares it for the potential implantation of an embryo.
What doctors look for is an endometrial thickness of at least 7-8 mm (3). The uterine lining should also have a trilaminar appearance – or triple line pattern – on an ultrasound.
Hormonal imbalances or disorders of the endometrium can make it harder to get pregnant. If you’re one of the 5% of patients undergoing an embryo transfer whose uterine lining is too thick (more than 14 mm), you may have more difficulty getting pregnant, and your chance of miscarriage is higher. Additionally, if your uterine lining is too thin, it could make your pregnancy more difficult. A 2022 study published in Frontiers in Endocrinology found that a thin uterine lining (less than 7 mm) can result in poorer pregnancy outcomes during IVF treatment. Possible complications include hypertension during pregnancy, low birth weight, and small-for-gestational-age infants (4). Fortunately, for patients undergoing IVF, a too-thin endometrium is not common; it occurs in just 5.5-6% of assisted reproductive technology cycles (5).
If you are diagnosed with a thin uterine lining without any other underlying conditions, your clinician may prescribe:
Interestingly, the research is unclear on whether a thick endometrium – more than 14 mm – affects embryo transfer. One study of 623 patients undergoing IVF found that the few patients with an endometrium thicker than 14 mm experienced lower implantation and pregnancy rates and higher miscarriage rates (9). However, another study of 4,911 SEET procedures (a type of embryo transfer) found that endometrial thickness up to 15 mm did not affect the outcome of the cycle (10).
Some uterine lining conditions may make it difficult to get pregnant, stay pregnant, or have a healthy pregnancy, even with IVF. These include:
Having one of these conditions may not affect your fertility and, in fact, you may not know you have one of these conditions before you try to become pregnant. For some people, though, these conditions can cause infertility and fertility treatments may be necessary to become pregnant.
For most people, before starting an IVF cycle, there are simple, science-supported steps you can take to optimize your uterine lining for embryo implantation.
The uterine lining is just one factor that contributes to whether or not you will be able to get and stay pregnant. Many people have had a successful and healthy pregnancy with a uterine lining below the ideal thickness, or with a condition that affects the uterine lining. Your fertility specialist and their team will give you guidance if steps need to be taken to optimize your uterine lining.
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