After How Many Days Can Pregnancy Be Detected?

This article is an excerpt from the Shortform summary of "Expecting Better" by Emily Oster. Shortform has the world's best summaries of books you should be reading.

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So you’ve been working hard to try to conceive, and now you want to see if you’ve successfully gotten pregnant. When you conceive, after how many days can you detect pregnancy?

Learn how many days it takes to confirm your pregnancy here.

How Many Days to Confirm Pregnancy

After you ovulate and try to conceive, it takes about 2 weeks to see if you have your period. But there’s a way to detect it faster – home pregnancy kits.

Home pregnancy kits cost ~$5 per test and measure hCG (human chorionic gonadotropin), which is produced by the implanted embryo (to maintain the corpus luteum in the ovaries, which then secretes progesterone). With these kits, the false negative rate is high – only 50% of pregnancies are detected 4 days before a missed period. But the false positive rate is very low – they are very unlikely to tell you you’re pregnant when you’re not.

One downside to early detection is that pregnancy loss is very common – as many as 50% of fertilized eggs don’t result in pregnancy. Normally this ends in what appears to be a heavy period. With early detection kits, you might learn you’re pregnant, only to lose it, which can be very disappointing. Some people may just choose not to detect early and just wait for their period.

Fun fact: hCG used to be detected by injecting urine into infantile mice or rabbits that were then dissected. If the urine contained hCG, the animals would ovulate. Some organizations now collect urine from pregnant women to extract hCG for fertility treatment.

What Do You Do While Waiting to Confirm Pregnancy?

No matter what, it takes about 2 weeks from conception to your period to figure out whether you’re pregnant. What do you do in this time – namely, can you drink alcohol or caffeine, and eat deli meats? (more on these later) Oster argues that embryos are more resilient than you might think – because the early embryo is a mass of pluripotent cells, any cells that are killed can be replaced by another cell. But there’s a limit – kill too many cells and the embryo will fail to develop.

If you want to stay on the cautionary side, then pretend you’re pregnant in the 2 weeks. Then on the day you find out you’re not pregnant, you can party if you want.

After How Many Days Can Pregnancy Be Detected?

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Like what you just read? Read the rest of the world's best summary of "Expecting Better" at Shortform. Learn the book's critical concepts in 20 minutes or less.

Here's what you'll find in our full Expecting Better summary:

  • Why much parenting advice you hear is confusing or nonsense
  • The most reliable way to conceive successfully
  • How much alcohol research shows you can drink safely while pregnant (it's more than zero)
  • The best foods to eat, and what foods you really should avoid

Allen Cheng

Allen Cheng is the founder of Shortform. He has a passion for non-fiction books (having read 200+ and counting) and is on a mission to make the world's best ideas more accessible to everyone. He reads broadly, covering a wide range of subjects including finance, management, health, and society. Allen graduated from Harvard University summa cum laude and attended medical training at the MD/PhD program at Harvard and MIT. Before Shortform, he co-founded PrepScholar, an online education company.

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