Understanding Progesterone: The unsung hero of fertility and early pregnancy

If you have begun to try for a baby or you are undergoing treatment such as IVF, you’ve likely heard about progesterone – a hormone that’s absolutely vital, yet often underappreciated in conversations around conception and early pregnancy. Let me take you back to basics and take you through exactly why progesterone is so important, how it functions in your cycle, and what signs might suggest you’re not producing enough of it.

The role of progesterone

Progesterone is a hormone naturally produced by the body and plays a crucial role in regulating the menstrual cycle and supporting early pregnancy. It’s particularly important in the second half of your cycle, known as the luteal phase – the time after ovulation and before your period.

Once ovulation has occurred, the follicle that released the egg transforms into a temporary gland called the corpus luteum. This structure is responsible for producing progesterone. Its job? To get your uterus ready for a possible pregnancy.

How progesterone supports pregnancy

As progesterone levels rise after ovulation, it works behind the scenes to create the ideal environment for conception. It does this by:

• Thickening the endometrial lining of the uterus, making it rich, cushioned, and receptive to implantation.
• Enhancing cervical mucus, helping sperm survive longer and travel more easily toward the egg.
• Calming uterine contractions, which could otherwise disrupt a fertilised embryo from implanting properly.

This hormonal symphony is critical to fertility – and when things go out of tune, it can affect your chances of conception or maintaining an early pregnancy.

Progesterone in early pregnancy

If fertilisation occurs and an embryo begins to implant, progesterone’s role becomes even more vital. During the first 8-10 weeks of pregnancy, the corpus luteum continues producing progesterone until the placenta is mature enough to take over.

In early pregnancy, progesterone:

• Maintains the thickened endometrium so it doesn’t shed (i.e., prevents a period).
• Supports the development of the placenta.
• Modulates the immune response to stop your body from rejecting the embryo – a crucial feature, as pregnancy is the only time the human body allows a “foreign” organism to thrive inside it.

Signs of low progesterone

Low progesterone can be an overlooked reason for fertility challenges or early losses. If your levels aren’t high enough during the luteal phase, it may prevent proper endometrial development or the successful maintenance of an early pregnancy.

Here are some common signs of low progesterone:

• Spotting before your period (often confused with implantation bleeding).
• A short luteal phase (less than 10 days between ovulation and menstruation).
• Difficulty conceiving despite regular cycles.
• A history of early miscarriage or biochemical pregnancies.

How I approach progesterone in fertility treatment

In my clinic, I am often dealing with clients who have very complex reasons for difficulty in conceiving but I take progesterone levels very seriously with all my clients. It’s one of the first things I check, yet despite more awareness of progesterone’s importance, it’s often missed elsewhere. A simple blood test around 7 days after ovulation can give us a good indication of whether your progesterone levels are optimal which is why I include this blood test in the Foundation Fertility Package.

If we find that your levels are low, the good news is that progesterone can be easily supported with supplementation—whether you’re trying to conceive naturally or undergoing treatments like IUI or IVF. During IVF, progesterone is routinely given in the form of pessaries, injections, or tablets after embryo transfer, and I am a fan of monitor your levels closely post transfer to ensure your body has all the support it needs.

If you’re experiencing symptoms of low progesterone or struggling with unexplained fertility challenges, I encourage you to book a consultation. Let’s dig deeper, get some answers, and support your body with the care it deserves.