How Hormones Prepare a Surrogate’s Body for Pregnancy

Introduction

Before a surrogate can carry a pregnancy, her body must be carefully prepared with hormones to create the ideal conditions for embryo implantation and fetal development. Since gestational surrogacy involves transferring an embryo created from the intended parents’ or donors’ genetic material, hormone therapy ensures the surrogate’s body is ready to support the pregnancy.

Key Hormones in the Surrogacy Process

One of the first hormones introduced is estrogen, which thickens the uterine lining (endometrium) to create a supportive environment for the embryo. Without enough estrogen, the uterus may not be receptive, reducing the chances of a successful implantation. Estrogen is usually given through pills, patches, or injections.

Next, progesterone is administered to stabilize the uterine lining and help maintain pregnancy. In a natural cycle, progesterone would be produced after ovulation, but since a surrogate isn’t using her own eggs, supplementation is necessary. This hormone is crucial for preventing early pregnancy loss and is typically given through injections or vaginal suppositories.

To regulate the timing of the embryo transfer, surrogates may also take gonadotropin-releasing hormone (GnRH) agonists, such as Lupron. These medications prevent natural ovulation, allowing doctors to synchronize the surrogate’s cycle with the embryo transfer schedule.

After the embryo transfer, human chorionic gonadotropin (hCG) may be used to further support early pregnancy. This hormone signals the body to keep producing progesterone, helping maintain the pregnancy until the placenta takes over hormone production around 10–12 weeks.

How Long Does Hormone Therapy Last?

Hormone therapy begins several weeks before the embryo transfer, as doctors gradually introduce estrogen and progesterone to prepare the uterus. These hormones continue to be administered after a successful embryo transfer to ensure the pregnancy remains stable.

Most surrogates will need to continue hormone treatments until 10 to 12 weeks of pregnancy. By this point, the placenta has developed enough to produce the necessary hormones on its own. Once the placenta takes over, hormone medications are gradually reduced and eventually stopped under medical supervision. Stopping hormone therapy too soon can increase the risk of pregnancy complications, so careful monitoring is essential.

Are There Side Effects of Hormone Therapy?

Like any medical treatment, hormone therapy can cause side effects, though they vary from person to person. Some common side effects include bloating, breast tenderness, mood swings, headaches, and fatigue. These symptoms are similar to those experienced during a natural menstrual cycle or early pregnancy.

Progesterone injections, in particular, can sometimes cause soreness at the injection site, while estrogen may lead to mild nausea or dizziness. Though these effects can be uncomfortable, they are usually temporary and manageable. Fertility doctors closely monitor surrogates throughout the process to ensure their health and well-being, adjusting dosages if needed.

Final Thoughts

Hormones play a vital role in preparing a surrogate’s body for pregnancy, ensuring a successful embryo implantation and early fetal development. Understanding this process can help both surrogates and intended parents feel more confident about the journey. If you’re considering surrogacy, consulting with a fertility specialist can provide clarity on the medical steps involved.