Embryo Transfer

Lining Prep: Why Estrogen is Prescribed During a Medicated Frozen Embryo Transfer Cycle?


2 min read

Many hormones play a role in successfully preparing your body for an embryo to implant and to carry a pregnancy. During a medicated embryo transfer cycle, your doctor will prescribe medications to take the place of the natural hormones that would occur during the menstrual cycle. One of the main hormones in this process is estrogen. 

Examples of estrogen medications.

Why estrogen?

In the natural menstrual cycle, estrogen is produced by the ovaries as the follicles develop. The rising estrogen levels trigger the estrogen receptors in the endometrium to start growing an endometrial lining in the uterus that is thick enough to support the implantation of an embryo. 

In a medicated embryo transfer cycle, your clinic will prescribe estrogen medications to replace what would normally be produced by your body. Estrogen can be prescribed in a few ways, tablets, patches, and injectable estrogen. 

  • Estrogen tablets (estrace) are tablets that can be taken orally or inserted vaginally. 

  • Estrogen patches are applied to the body and the hormone is absorbed through the skin. The patches are typically placed on the lower abdomen or back of the arm where there is enough subcutaneous fatty tissue to absorb the medication.

  • Injectable Estrogen (estradiol valerate) is another common type of estrogen used for endometrial prep before an embryo transfer. Injectable estrogen is given intramuscularly. The most common injection location is the upper, outer quadrant of the butt.

Depending on how your body responds, your doctor may prescribe you one or a few of these types of estrogen. Most people take estrogen alone for 10-14 days before having an ultrasound to check their lining to see if it is sufficient to start progesterone, which the next step in preparation for the embryo transfer. 

The typical goal for endometrial lining thickness is around 7mm or greater. Additionally, your doctor will want to see that the lining has a “trilaminar” pattern when visualized on ultrasound. Trilaminar refers to a 3 line pattern that indicates that the lining has responded well to the estrogen.

Ultrasound image of a trilaminar uterine lining

After your doctor confirms that your lining thickness and pattern are optimal, your clinic will work with you to schedule your embryo transfer date and give you instructions on when to start your progesterone medication.

If you want to learn more about progesterone and its role in a medicated embryo transfer, check out our article here.