How are babies made?

Think you know? Put your knowledge to the test.

Hello, and welcome to a very belated installment of So When Are You Having Kids: The Newsletter. There are a lot of new faces here, welcome. A lot of you came from a certain Facebook post sharing parenthood surveys related to my book. Thanks for filling those out. I am still working on the book, but you can expect to hear if your response made it in over the next few months.

I should probably start by mentioning that this email is not safe for work. Although, I spent three hours reading about sperm as part of my workday, so I suppose what is and isn’t safe for work depends on what you do for a living (and how much your employer monitors your computer).

It’s incredible how little people know about their fertility. Abstinence-only education aside, even comprehensive health classes skip over fertility. The assumption is, at least in high school, that everyone is one second away from impregnating someone or being impregnated.

The reality looks a bit different. A lot of things have to go right in order to conceive. Sure, some people get pregnant quickly, but others don’t. The more you learn about conception, the more surprising it is that anyone gets pregnant at all.

Think you know your stuff? Pop quiz time. Let’s go.

How long does it take sperm to get from the vagina to the fallopian tube?

  1. 12 hours

  2. 4 hours

  3. 2 hours

  4. 45 minutes

  5. 5 minutes

Once sperm exits the uterus, it can immediately fertilize an egg.

  • True

  • False

How long can sperm survive once it enters the vagina?

  1. up to 5 days

  2. up to 3 days

  3. up to 2 days

  4. up to 1 day

  5. 12 hours

How long can an egg survive?

  1. 4 to 5 days

  2. 2 to 3 days

  3. 1 to 2 days

  4. 12 to 24 hours

  5. 6 to 12 hours

How long does it take an embryo to reach the uterus and implant?

  1. 12 - 24 hours

  2. 1 - 3 days

  3. 3 - 5 days

  4. 6 - 10 days

  5. 11 - 14 days

Pencils down! How do you think you did? If this was harder than you expected, don’t feel bad. I highlighted these questions in particular because they are some of the most useful if you are trying to conceive or preventing it. If you don’t understand your cell-by date (pun intended), you’re leaving a lot up to chance.

Let’s see how you did.

How long does it take sperm to get from the vagina to the fallopian tube? The answer is 5) 5 minutes! While you might just be learning this, scientists figured this out in 1973. Researchers inseminated women undergoing surgery to remove their Fallopian tubes and found it took 5 minutes for sperm to go from the vagina to the tubes. But don’t give the sperm all the credit for getting there so quickly. It turns out that vaginal, cervical, and uterine contractions help a lot of the transport. And just because it takes some sperm five minutes doesn’t mean all sperm make it there that quickly. The sperm that get there first, in most cases, are not the fertilizing sperm. Sperm also stays behind in the cervical mucus and cervix itself. The cervix and its mucus both play a fairly critical role in fertilization. The mucus stops atypical sperm from passing through and folds within the cervix can store sperm for several days.

Once sperm exits the uterus, it can immediately fertilize an egg. FALSE! Some sperm might make it to the tube in five minutes, but that doesn’t mean it can fertilize an egg immediately. Sperm has to go through a process called capacitation. Studies looking at fertilization outside of the human body show capacitation time ranges from 3 to 24 hours. It’s an asynchronous process, meaning groups of sperm undergo it at different times to prolong their fertilization potential.

How long can sperm survive once it enters the vagina? You’re number 1 if you said answer choice 1) up to five days. Sperm live on average three days, but they can survive up to five days under the right conditions. That’s why you have a chance of getting pregnant days before you ovulate; the sperm hangs around. Research shows sex the day before ovulation results in the most clinical pregnancies. Sex the day of ovulation also results in a high pregnancy rate, but the miscarriage rate for those pregnancies is higher.

How long can an egg survive? If you said 4) 12 to 24 hours, then you are correct! Eggs do not last very long. Yet another reason why the sperm should be waiting for the egg and not the other way around.

How long does it take an embryo to reach the uterus and implant? Given how quickly everything else happens, you might have thought this process is relatively quick too. Not so much. The answer is 4) 6 to 10 days. Once the egg is fertilized, it sits in the Fallopian tube for 30 hours, just chilling, I mean, just undergoing cell division. From there, it makes its way out of the tube and into the uterus. After five to six days, the embryo hatches out of its shell, known as the zona pellucida, and starts to embed into the uterus. Most implantation occurs on days 8-10. The later implantation occurs, the less likely the odds of a successful pregnancy. For pregnancies where implantation happened on the ninth day, 13 percent ended in early loss. The risk of miscarriage rose to 26 percent with implantation on day 10, 52 percent on day 11, and 82 percent after day 11. Pregnancy tests can only detect hcg following implantation.

So, how did you do?

If you got all five correct, my guess is either you work in reproductive medicine or have been trying to conceive for quite some time. If it’s the latter, hang in there. You got this.

If you got more than three questions correct, color me impressed. Nice job.

Less than three? Ok. Well, now you know!

Zero? Oof, let me guess. Your high school taught abstinence-only.

Timing is key when it comes to planning or avoiding pregnancy. If you want to get pregnant experts suggest having sex every one to two days to maximize your odds. Sex every day gives you slightly higher odds (37% compared to 33%). Most people without fertility challenges, about 80%, will get pregnant within 6 months of trying. If you want to avoid getting pregnant and aren’t using birth control, knowing when you ovulate is key. And, if you cannot conceive through intercourse, understanding the ins and outs of sperm and egg cells can help you understand what’s happening during artificial insemination or IVF.

Thanks for playing along. If you feel brave enough, post your score in the comments. I’d love to know how everyone did. No shame!

Until next time,


P.S. This newsletter will continue once a month until 2022, at which point I’m hoping to have new editions go out twice per month. If you like the newsletter, tell a friend. Have a topic you’d like to see covered in a future newsletter? Reply to this email and let me know.