Week 4
If you conceived, this is the week the embryo finishes burying itself in the lining of your uterus and starts sending out hCG, the pregnancy hormone. It is one to two weeks old, a flat disc of cells far too small to see without a microscope, about 0.1 to 0.2 mm across. Around it, the beginnings of the placenta, the amniotic sac, and the yolk sac are taking shape. Babies vary, and so does the timing of implantation by a few days.
Your period is due at the end of this week if your cycle is about 28 days. Some people notice light spotting, tender breasts, or unusual tiredness, while many notice nothing at all. This week is about understanding pregnancy tests: how they work, when to take one, and how to read the result.
Day 22 · 3 weeks 0 days
The embryo is settling deep into its new home
By about now, eight days after fertilization, the blastocyst is sinking fully into the lining of your uterus. Within a few more days, the surface of the lining will close over it completely. From then on, it grows inside the wall of the uterus, not in the open space within it.
The lining itself changes in response. Its cells swell with nutrients and it becomes a specialized tissue called the decidua. This tissue feeds the embryo in the earliest days, before the placenta can take over, and it forms the maternal side of the placenta later.
Meanwhile, the outer trophoblast cells are spreading through the lining in finger-like strands. They tap into small blood vessels and form tiny spaces that fill with your blood. This is the very first step toward the placenta, the organ that will exchange oxygen, nutrients, and waste between you and your baby for the rest of pregnancy.
Inside, the flat disc of embryonic cells now has two distinct layers. A small fluid-filled space above it will become the amniotic cavity, and the sac below it is the beginning of the yolk sac.
Try this: Keep up your folic acid and prenatal vitamin every day this week. The embryo's nervous system starts forming within about a week.
Day 23 · 3 weeks 1 day
Light spotting around now can be normal
Some people notice a little spotting about 10 to 14 days after conception, around the time their period would be due or just before. This is often called implantation bleeding. It is thought to happen as the embryo burrows into the blood-rich lining of the uterus.
Implantation spotting is usually light: a few drops, or a pink or brown streak when you wipe. It typically lasts from a few hours to a couple of days and does not need a pad. It may come with mild cramps. Many people never have it, and that is just as normal.
It can be hard to tell from a light period. A period usually starts light, then gets heavier and redder, and includes clots for some people. Spotting stays light. If you are unsure, a pregnancy test a few days later will give a clearer answer.
Spotting in the first weeks of pregnancy is common and often harmless, but it is always worth mentioning.
Call your care provider if you have bleeding that is as heavy as a period or heavier, bleeding with cramps that are getting worse, or any bleeding after a positive pregnancy test. Get help right away if you have severe pain in your belly or shoulder tip, or feel faint or dizzy.
Try this: If you notice spotting, jot down the date, colour, and amount. It will be useful information if you later need to describe it.
Day 24 · 3 weeks 2 days
hCG is the hormone that says you are pregnant
Human chorionic gonadotropin, or hCG, is made by the cells that will form the placenta. It appears only in pregnancy, which is why tests look for it. Its main job in these early weeks is to keep the corpus luteum in your ovary making progesterone, so the uterine lining stays in place and your period does not come.
The amount rises fast. In a healthy early pregnancy, hCG roughly doubles every two to three days for the first several weeks. It peaks around 8 to 11 weeks and then falls to a lower level for the rest of pregnancy. hCG shows up in your blood first, around 8 to 11 days after conception, and in your urine a little later. A blood test at a clinic can measure the exact level. That is sometimes done to follow a pregnancy closely, for instance after fertility treatment or if there are concerns. For most people, a home urine test is all that is needed.
Rising hCG is also linked to some early symptoms, including nausea. Its levels vary widely between healthy pregnancies, so a single number on its own says little. What matters more is how it changes over time, and your care provider will interpret that if it is ever needed.
Try this: Check the use-by date on any pregnancy tests you have at home, since old tests can be less reliable.
Day 25 · 3 weeks 3 days
A home test works best from the day your period is due
Home pregnancy tests detect hCG in urine. They are accurate and inexpensive, and a basic store-brand test works as well as a costly one. Most give a result in a few minutes, as lines, a symbol, or words on a digital display.
Timing matters more than brand. Some tests claim to detect pregnancy several days before a missed period. They can, but only if hCG has already risen enough, which depends on when you ovulated and implanted. Testing early often gives a negative result even when you are pregnant. From the first day of your missed period, most tests are reliable.
A few tips help:
Use your first urine of the morning if you are testing early, as it is the most concentrated.
Avoid drinking a lot of fluid just before testing.
Follow the instructions exactly, including how long to wait before reading.
Read the result within the time the instructions give.
If your cycles are irregular, count from the longest cycle you usually have, or simply test about three weeks after you last had sex without contraception.
For your partner: Offer to pick up a test, and ask whether your partner would like you there when they take it or would rather have some time alone first.
Day 26 · 3 weeks 4 days
A faint line usually still means yes
Reading a pregnancy test is not always as simple as the box suggests. Here is what different results usually mean.
A clear line, or "pregnant" on a digital test, is a positive result. False positives are rare. They can happen with some fertility medicines that contain hCG, with a very recent pregnancy loss, or, uncommonly, with certain medical conditions.
A faint line that appears within the reading time, and has some colour, is usually positive too. It often means hCG is still low because it is early. Testing again in two or three days should show a darker line.
A thin, colourless, or grey line that appears only after the reading time is often an evaporation line and does not count. This is why the timing in the instructions matters.
A negative result means no hCG was detected yet. If your period still has not come, test again in a few days. If you have had two negative tests a week apart and still no period, contact your care provider to look for another cause.
Sometimes a test is positive and then a period arrives a few days later. This is a very early pregnancy loss, often called a chemical pregnancy. It is common, and week 5 talks about it more fully.
Try this: If your result is faint or unclear, put the next test date in your calendar for two or three days from now rather than testing every few hours.
Day 27 · 3 weeks 5 days
Sore breasts and deep tiredness can come early
For some people, the first sign of pregnancy is not a test but a feeling. Two of the most common early signs are tender breasts and an unusual tiredness, both driven by rising hormones.
Breasts may feel full, heavy, tingly, or sore to touch, a bit like before a period but often stronger. The areolas, the darker skin around the nipples, may darken and the small bumps on them may become more noticeable. A soft, supportive bra without underwire, including at night if it helps, can make a real difference.
The tiredness can be striking. Rising progesterone has a sedative effect, and your body is working hard to build a placenta and increase your blood volume. Many people say it feels like a heavy fog by mid-afternoon. It usually eases in the second trimester.
Other early signs include needing to pee more often, a metallic taste, bloating, mild cramps, and feeling more emotional. Nausea often starts in the next couple of weeks.
You may have all of these, a few, or none. Having no symptoms is not a sign that something is wrong. Symptoms vary from person to person and from one pregnancy to the next.
Try this: Plan a short rest or an early night today, and let one non-essential job wait until tomorrow.
Day 28 · 3 weeks 6 days
Three structures are forming to support your baby
While the embryo itself is still tiny, the support system around it is growing fast. Three structures are especially important in these weeks. The first is the early placenta. The trophoblast cells have grown tiny branching projections called chorionic villi into the lining of your uterus. Over the coming weeks, these villi will multiply and fill with blood vessels, creating a huge surface for exchanging oxygen and nutrients with your blood. Your blood and your baby's blood stay separate the whole time.
The second is the amniotic sac. It begins as a small fluid-filled space above the embryonic disc, and it will grow to surround the baby completely, cushioning it in amniotic fluid.
The third is the yolk sac, a small balloon-like structure below the disc. In humans it does not hold yolk. Instead, it supplies nourishment in the earliest weeks and makes the first blood cells until the liver and placenta take over. It is often the first structure seen inside the pregnancy sac on an early ultrasound.
The embryonic disc between the amniotic sac and yolk sac is about to start organizing into the layers that become every part of your baby. Try this: If your period is due today or tomorrow, and you have chosen a date to test, keep a test somewhere easy to reach in the bathroom.