When I was a teenager, I thought pregnancy was lurking behind every corner. Get too close to someone with opposite genitalia, and babies will practically rain from the heavens.
Okay, so maybe it’s a touch more complicated than that. How does it all work? Let’s get down to the details of getting pregnant, in laymen’s terms.
If you have a uterus and ovaries, you’ve had a collection of eggs since before you were born. They sit there, waiting. And waiting. And waiting. Not all of them will be ready for game day. Some may have chromosomal glitches, little details that make them unsuitable for fertilization. But come puberty, once a month (on average), one (on average) will make the trek through your fallopian tube into your uterus.
So what’s the difference between ovulation and menstruation. Picture your uterus as a hostess. She’s planning a party! She plans it every month, and never gets tired of it. She’s expecting a fertilized egg. She starts decorating, making a nice soft lining for that fertilized egg to implant into. And sometimes, her guest will arrive. Usually, the guest of honour is a no show, with an uninvited guest showing up instead. Our good hostess just hates that. She tears down all her decorations and shows the uninvited guest the door.
Midway through your cycle, an egg will release. That’s ovulation. If that egg is unfertilized, it will pass along with the uterine lining. That’s menstruation.
Let’s say you’re more of the testicular persuasion. Where your ovarian counterparts stress quality over quantity, testes go the opposite route. An army of sperm cells are in production at all times, and a single ejaculation sends out millions upon millions of them. There’s strength in numbers. Not all of those sperm will be viable. Not all will be good swimmers. Not all will survive the long journey. Not all will be able to penetrate the egg. Sending off millions of applicants helps to ensure at least one will be right for the job.
The trick is getting sperm and egg to arrive in the same place at the same time. Those of us with uteri are not fertile at all times. A viable egg leaves the ovary at roughly day 14 of your cycle (take an ovulation test to be sure) and will begin it’s journey through the fallopian tube. Sperm must be able to meet the egg on its journey for conception to occur.
The big meeting has occurred! Our hostess is still decorating for the upcoming party, and the sperm and egg are getting to know each other. At this point, no other sperm in the area will be able to penetrate the egg. This is an “admit one only” get together. You’ve conceived, but you still aren’t “officially” pregnant. Two things have to happen from here for pregnancy to occur. The fertilized egg must begin cell division and growth, and it must implant into the uterine lining. A portion of fertilized eggs won’t accomplish these tasks, and will simply pass with the next menstrual period. A small percentage will begin cell division, but never exit the tube. This is a ectopic, or tubal pregnancy and is both extremely dangerous, and incompatible with fetal life in all but the rarest cases.
In our hypothetical, cell division has begun, and the journey through the fallopian tube continues unobstructed. This journey will take about four days. Your egg is now a zygote, with two distinct parts. An outer layer, destined to become a placenta and other tissues, and an inner layer destined to become a fetus. On the fifth day, the zygote will arrive in the uterus and “hatch” out of its self containment. It’s ready to implant.
Some may experience spotting associated with implantation, and may even mistake it for a slightly early period. This is called implantation bleeding. From implantation, human chorionic gonadotropin or HCG and other pregnancy hormones trigger production. The cervix will seal itself with a mucous plug. The cells will continue dividing and become an embryo. You’re approaching your expected period, and when you test, you’ll get a positive result. Congratulations! You’re pregnant. If all goes well, 40 weeks from your last period (two weeks before the egg even left your ovary) a new family member will arrive.
It’s a complicated process, planning that party your uterus is throwing. Every little detail, twist of fate, moment in time, contributes to the creation of each unique human being.