What is conception? Fertilization & implantation explained

What is conception?

Put very simply, conception is what happens when a sperm cell and an egg cell join together, and it’s a critical step in pregnancy. 

When a male ejaculates, millions of sperm cells are released – and they all have one goal: to find an egg to fertilize. Many of the sperm won’t survive the journey, but those that do will travel to the fallopian tubes in search of an egg to fertilize. If there is an egg, and it meets with a sperm, then the egg can be fertilized and conception can happen.

How does conception occur?

The process sounds simple, but it’s a lot more complicated than simply ‘sperm meets egg’ — there’s a lot going on behind the scenes to make conception happen! Let’s dive into the process in more detail.

How the cervix and vagina prepare for pregnancy 

Before discussing the details of conception, it’s important to understand how ovulation works. Ovulation occurs when a mature female egg cell is released from an ovary. The egg cell lives for up to 24 hours after it’s released, and if it’s not fertilized, it dies.

In the days before ovulation (which takes place at the end of the first phase in the menstrual cycle), your cervix starts to prepare for the release of an egg. The cervix produces cervical mucus, a fluid that changes in texture across your menstrual cycle and can be used (along with other fertility indicators) to identify when you’re at your most fertile. 

Just before ovulation, your cervical mucus changes texture to become clear with a slippery consistency. This makes it easier for sperm to travel through the cervix, meaning sperm is more likely to be able to reach an egg in the fallopian tube.

How the uterus prepares for pregnancy

During this time, your uterus is also preparing for conception and to receive a fertilized egg. The lining of your uterus is known as the endometrium. During your period, you shed this lining. Then, during the course of your menstrual cycle, the endometrium starts to thicken after ovulation. This thickened lining provides a nourishing environment for the embryo to implant and grow if fertilization occurs.

How the uterus interacts with sperm

During sexual intercourse, sperm are ejaculated into the vagina. The sperm cells then swim through the cervical mucus and into the uterus. 

A huge number of sperm die after being released, and only a small number of sperm will reach the fallopian tubes, where fertilization typically occurs.

How does fertilization work

Once the sperm have reached the fallopian tube and met the egg, there’s no guarantee that conception will occur — as a sperm still needs to successfully penetrate and fertilize the egg.

The sperm release enzymes that help them penetrate the outer layer of the egg.The enzymes bind to receptors on the surface of the egg, which changes the egg’s membrane and prevents other sperm cells from binding with the egg – ensuring that only one sperm can fertilize the egg. 

The sperm then fuses with the egg by merging its membrane with the egg’s membrane to form a single cell called a zygote —this is the process of fertilization.

If a sperm doesn’t fertilize the egg, then the egg dissolves, and your menstrual cycle continues. If the egg is fertilized, then it’ll start to move from your fallopian tube to your uterus while dividing itself. Once it reaches your uterus, the cluster of cells (known as a blastocyst) can attach itself to the wall of your uterus in the process of implantation.

Conception vs. implantation

Conception and implantation are two distinct stages in the process of pregnancy:

• Conception is the moment when a sperm cell fertilizes an egg cell, leading to the formation of a zygote as the genetic material from the sperm combines with the egg’s genetic material to form a single cell.
• Implantation occurs after conception and refers to the process by which the fertilized egg, now called a blastocyst, attaches to the lining of the uterus (known as the endometrium).

Just because conception occurs doesn’t mean that implantation will. It’s thought that between one-third and one-half of all fertilized eggs never fully implant [1]. You probably won’t be aware if this happens, and will likely get your period as normal.

Timeline of getting pregnant

Conception can lead to pregnancy, but it doesn't always — and a person isn't technically considered pregnant until implantation has occurred. 

Plus, it’s important to know that it’s not always possible to get pregnant when you have sex. To get pregnant, you have to have sex during your fertile window— and there are only six fertile days in any cycle. 

To get pregnant, you need to have sex within your fertile window, and a sperm has to successfully fertilize an egg cell, as outlined above. This can lead to implantation, which marks the official start of pregnancy. The timeline for getting pregnant, then, looks like this:

• Day 1: First day of your period
• Ovulation day : You ovulate, releasing an egg from one of your ovaries (ovulation day can vary significantly from person to person and cycle to cycle). [2]
• Within 24 hours of ovulation: The egg can be fertilized by sperm if you’ve had sex in the last few days without using contraception
• Around 8-10 days after ovulation: the fertilized egg attaches itself to the wall of the uterus, known as implantation — which is when pregnancy begins [3].
• After another 5 to 7 days: You will likely get a positive result when taking a pregnancy test — this is around the time your period should be due.

Although you’re pregnant from the time of implantation, it may take a few days before a pregnancy test picks this up. That’s because pregnancy tests work by detecting a hormone called human chorionic gonadotropin (hCG) in your urine. hCG can be found in your blood around 11 days after conception, but it can take longer for it to show up in your urine — which is why we recommend taking a pregnancy test on the first day of your missed period.

When should I have sex to conceive?

You’re fertile for just six days per cycle — and there are two days (the day of ovulation and the day prior to ovulation) during which you have the highest chance of conceiving – so if you’re planning a pregnancy, it’s important to know when that fertile window is. 

Did you know that sperm can survive for up to five days in the female reproductive system? However, the longer time goes on, the more sperm begin to die off. Therefore to increase your chances of getting pregnant, you can try to time sex on the day before or the day of ovulation. This gives sperm cells time to reach the egg cell before either starts to deteriorate. 

Natural Cycles can help take the guesswork out of pregnancy planning by helping you pinpoint your fertile window. Our algorithm can find your ovulation day and the days when you’re most likely to get pregnant by analyzing your body temperature and luteinizing hormone levels. 

How does conception work with IVF?

The process of conception is similar to in vitro fertilization (IVF), in that sperm must fertilize an egg. However, this typically happens in a lab with IVF, rather than inside the female reproductive system.

During IVF, your healthcare provider will retrieve eggs from the ovaries. Sperm is collected from either the male partner or from a sperm donor. The eggs are then combined with the sperm in a laboratory – or alternatively, a single sperm may be injected directly into each mature egg to facilitate fertilization.

The eggs are then incubated and monitored for signs of fertilization. The embryos are then transferred to the uterus, and if successful, they implant into the uterine lining, and pregnancy begins.

Understand your fertile window

Getting to grips with your own fertile window is a useful skill if you’re planning to get pregnant. It can help you to understand when the best time to have sex is if you want to conceive. Natural Cycles can support you on your fertility journey, we’ll help you find your ovulation day and so you can get pregnant faster. Research shows that couples who used NC° to get pregnant did so in three cycles on average.[3] To date, we’ve helped more than 3 million women plan and prevent pregnancy worldwide. Why not find out if we could support you, too?