Embryo Transfer

Lining Prep: Why Progesterone is Prescribed During a Natural Frozen Embryo Transfer Cycle

Laura Morrissey, RN, BSN

3 min read

Many hormones play a role in successfully preparing your body for an embryo to implant and to carry a pregnancy. During your natural embryo transfer cycle, your doctor will prescribe supplemental progesterone medication to boost the natural hormones that would occur during your cycle. 

After your body naturally grows a follicle, produces estrogen to grow the endometrial lining, and ovulation occurs, your body will start producing progesterone. It is common for your doctor to prescribe progesterone supplements to boost your natural progesterone production and  ensure that there is adequate progesterone within your body to help to maintain a pregnancy.  

Why progesterone?

In the natural menstrual cycle, progesterone is produced by the remnants of the follicle that ovulated this month. This structure is known as a corpus luteum. The progesterone produced by the corpus luteum is not only necessary to change the lining texture for embryo implantation, but it is also responsible for maintaining the pregnancy until the placenta takes over at around 10 weeks of gestation. 

The supplemental progesterone can be prescribed in a few ways, vaginal inserts, vaginal gel, and injectable progesterone. Vaginal progesterone is the most common type prescribed during natural frozen embryo transfer cycles.

  • Vaginal Progesterone inserts are capsules that contain a cream-like progesterone inside. Many of the inserts come with an applicator that is used to insert the capsule deep into the vagina near the cervix. Once in the vagina, the outer shell of the capsule breaks down and releases the progesterone where it is absorbed through the mucous membranes of the vaginal wall. 

  • Vaginal progesterone gel works similarly to the capsules, but rather than inserting a capsule vaginally, the gel is dispensed into an applicator and the gel itself is placed in the vagina. The progesterone hormone is then absorbed from the gel through the vaginal wall where it enters circulation.

  • Injectable progesterone is mixed in oil, so you can expect that it can be quite thick when drawing up the medication and depressing the plunger to inject it.  There are a variety of oil preparations to choose from, the most common is ethyl oleate, but other common options are olive oil and sesame oil. The injectable progesterone is given through an intramuscular injection. The most common location for these injections is the upper, out quadrant of the butt. 

Click here to read more about how to do intramuscular injections like a pro.

Examples of vaginal and injectable progesterone.

  1. Vaginal progesterone (both capsule and gel) tends to leak out after inserting. This is normal and doesn’t mean that it isn’t working! It is recommended to wear a panty liner and change it frequently to prevent skin irritation.  

  2. Injectable progesterone in oil can leave knots or bumps under the skin after injecting. Two ways to help avoid this are to massage the injection site gently after the injection to help disperse the medication and a warm compress on the injection site following the injection. Be sure not to ice the progesterone injection site as this can coagulate the oil and make it harder to absorb. 

When to take progesterone

Your clinic will instruct you on when to start the supplemental progesterone based on when you ovulate. Once ovulation is confirmed, you will also be informed what day your embryo transfer will take place.

The progesterone is continued at least through the blood pregnancy test that takes place 9-14 days after the transfer. If the pregnancy test is positive, the progesterone is often continued for another 3-6 weeks when the placenta will take over the production of progesterone to maintain the pregnancy.