The Playbook

3 Weeks Pregnant: Conception and Implantation for Dads

By the Guide to Fatherhood editorial team. Last reviewed . 2 min read.

Checked against guidance from organizations like the AAP, CDC, ACOG and NHS (linked below). This is general information, not medical advice. Read our medical disclaimer.

Trimester1
Sizea pinpoint (a ball of cells)
Lengthabout 0.1 to 0.2 mm

If an egg was fertilized, it is now a rapidly dividing ball of cells (a blastocyst) traveling down the fallopian tube toward the uterus, where it begins to implant.

Your to-do list this week

  • Don't push for early tests. Home tests usually can't detect pregnancy until around the time of a missed period.
  • Keep life normal: plan the weekend, go for walks, do things that have nothing to do with the two-week wait.
  • Take over anything stressful you can for a couple of weeks: errands, the dinner plan, the in-law phone call.
  • Read up on early pregnancy warning signs, just so you know them: heavy bleeding or severe one-sided pain means calling a doctor.
A conversation to have this week

"How are you holding up with the waiting?" Some people want to talk about it constantly; others want a total distraction. Ask which kind of week she wants.

Conception, in about 200 words

If sperm met the egg in the fallopian tube around the end of last week, fertilization creates a single cell with a full set of DNA, half from each of you. Within hours it starts dividing. Over the next several days it becomes a hollow ball of cells called a blastocyst as it travels down the tube toward the uterus (Cleveland Clinic).

Around six to ten days after fertilization, the blastocyst burrows into the lining of the uterus. That’s implantation. Some cells will become the embryo; others will become the placenta, which will feed and support the baby for the rest of the pregnancy (ACOG).

Only after implantation does her body start making hCG, the hormone pregnancy tests detect. That’s why testing this week is almost always too early.

How she may be feeling

Usually, no different. A few people notice mild cramping or light spotting around implantation. Emotionally, though, week 3 can be a long one if you’re trying. The waiting is real, and it’s often harder on the person whose body is involved.

Your job this week: stay steady

There’s nothing to measure or schedule. The most useful things you can do are ordinary:

  • Keep evenings and weekends full of normal life.
  • Take a few things off her plate without being asked.
  • Don’t be the one who suggests testing early, then gets weird about a faint line.

One thing worth knowing

Very rarely, a fertilized egg implants outside the uterus, most often in a fallopian tube. That’s an ectopic pregnancy, and it can be dangerous. According to ACOG, warning signs include abnormal vaginal bleeding, low back pain, mild pain in the abdomen or pelvis, and mild cramping on one side of the pelvis; severe pain, dizziness or fainting, or shoulder pain need emergency care. You won’t need this information most of the time, but you should have it.

Frequently asked questions

When can a home pregnancy test detect pregnancy?

Home tests detect the hormone hCG, which only starts being produced after implantation. Most give reliable results from around the first day of a missed period. Testing earlier often gives a false negative.

Is spotting in week 3 normal?

Light spotting around implantation can happen and is usually harmless. Heavy bleeding, or bleeding with severe pain, especially on one side, should be checked by a doctor.

Sources

  1. Fetal development: Stages of Growth, Cleveland Clinic
  2. How Your Fetus Grows During Pregnancy, American College of Obstetricians and Gynecologists
  3. Ectopic Pregnancy, ACOG

We link to the original source for every medical and safety claim. Guidance changes; if a source has been updated since our last review, the source wins. How we research.