Progesterone Levels After Embryo Transfer: What to Know

After embryo transfer, progesterone is the hormone that maintains the uterine lining and supports early pregnancy until the placenta takes over at 8–10 weeks. In IVF — especially frozen embryo transfers — the body's natural progesterone production is either absent or insufficient, making supplementation critical. Understanding target levels, supplementation options, and what low levels mean helps you navigate the anxious post-transfer waiting period with better information.

Why Progesterone Matters

Progesterone transforms the estrogen-primed endometrial lining into a secretory state that's receptive to embryo implantation. It suppresses uterine contractions that could expel the embryo, supports decidualization (the process that makes the lining hospitable to an implanting embryo), and maintains the lining until the developing placenta produces enough progesterone on its own — typically around weeks 8–10 of pregnancy.

In natural conception, progesterone is produced by the corpus luteum (the structure left on the ovary after ovulation). In medicated FET cycles, there is no corpus luteum — progesterone is entirely supplied by supplementation. In fresh transfer cycles, the corpus luteum exists but may produce suboptimal progesterone, so supplementation is still standard.

Target Levels

Target serum progesterone levels vary by supplementation route and clinic protocol, but general guidelines include:

Supplementation Routes

Intramuscular progesterone in oil (PIO): The traditional gold standard — daily injections in the upper outer quadrant of the buttock. Delivers consistent, measurable serum levels. Downsides: painful injections, injection-site reactions (knots, swelling), and need for a partner or self-injection skill. Oil options include sesame, olive, or ethyl oleate (thinner and easier to inject).

Vaginal progesterone: Available as suppositories (Endometrin, compounded progesterone), gel (Crinone), or capsules (Utrogestan used vaginally). Advantages: no injections, high uterine tissue levels, and self-administered. Disadvantages: vaginal discharge, variable serum levels that complicate monitoring, and some evidence suggesting slightly lower pregnancy rates in medicated FET cycles compared to IM — though this remains debated.

Subcutaneous progesterone: Newer formulations (such as Prolutex) deliver progesterone via small subcutaneous injections — less painful than IM and with measurable serum levels. Availability varies by country.

Oral progesterone: Oral micronized progesterone (Prometrium/Utrogestan) is convenient but poorly absorbed — serum levels are low and inconsistent. Generally considered inadequate as the sole supplementation method for IVF, though sometimes used as an adjunct.

What If Levels Are Low?

Finding low serum progesterone after transfer triggers anxiety, but the response depends on context. If you're on vaginal-only supplementation, low serum levels may not reflect uterine levels and may not be clinically significant. If you're on IM injections and levels are below 15 ng/mL, most clinics will increase the dose or frequency. Some clinics switch to or add IM injections if vaginal-only levels are concerning.

The key principle: low progesterone that's caught and corrected early generally doesn't compromise outcomes. The concern is undetected, persistently inadequate progesterone that leads to endometrial breakdown before the pregnancy is established.

Monitoring Schedule

Monitoring practices vary by clinic. Common approaches include checking serum progesterone on the day of or day before transfer (to confirm adequate preparation), rechecking 5–7 days post-transfer, continuing weekly checks through weeks 6–8 of pregnancy, and tapering supplementation at weeks 10–12 (after placental progesterone production is established). Some clinics don't routinely monitor serum progesterone at all, instead relying on standardized supplementation protocols — this is a legitimate approach if the protocol is robust.

How Colombian Clinics Handle This

Colombian fertility clinics generally follow modern progesterone supplementation protocols — IM, vaginal, or combined — with monitoring tailored to the supplementation route. For international patients who transfer in Colombia and return home for early pregnancy monitoring, your Colombian RE will provide a progesterone supplementation protocol and coordinate with your local OB/GYN for ongoing monitoring and eventual taper.

Progesterone medications are significantly less expensive in Colombia than in the US — both IM preparations and vaginal formulations can be purchased at local pharmacies at a fraction of US prices. Some patients stock up on supplies during their treatment trip to carry home for the supplementation period.

Explore Our Colombia Medical Network