Week 3
This is the week a pregnancy usually begins. If an egg meets a sperm in the fallopian tube, the two cells fuse into one, and that single cell starts dividing as it drifts toward the uterus. By the end of the week, a hollow ball of cells called a blastocyst, smaller than the dot on this "i", is starting to settle into the lining of your uterus. Remember the two-week gap: by gestational age you are 2 weeks along, but your future baby is only hours or days old.
You will not feel any of this, and no test can detect it yet. Keep taking folic acid, stay clear of alcohol and smoke, and keep caffeine moderate. This is also the start of the two-week wait, which can be harder on the nerves than people expect.
Day 15 · 2 weeks 0 days
Two cells become one
Of the tens of millions of sperm that may enter the vagina, only a few hundred reach the egg in the fallopian tube. They cluster around its outer layer, and one finally gets through. The moment it does, the egg's surface changes chemically and locks the others out.
That is fertilization. Over the following hours, the genetic material from the egg and the sperm comes together. The result is a single new cell, called a zygote, with a full set of 46 chromosomes: 23 from each biological parent.
That one cell holds the instructions for an entire person. Eye colour, blood type, and countless other traits are already written into it, along with genetic sex. The egg always carries an X chromosome. The sperm carries either an X or a Y, so the sperm decides whether the chromosomes are XX or XY.
You cannot find out any of this for many weeks yet, and nothing you do now changes it. Fertilization happens quietly and without any sensation. If someone tells you they "felt" conception, it is a lovely story, but there is no physical sign at this stage.
Try this: Keep taking your folic acid today as usual. If this is the cycle, your baby's neural tube will start forming within about three weeks.
Day 16 · 2 weeks 1 day
The first divisions happen on the move
About a day after fertilization, the zygote divides into two cells. Then two become four, four become eight, and so on, roughly once a day at first. The cells do not grow larger as they divide. The whole cluster stays about the size of the original egg, so each new cell is smaller than the last. All of this happens while the cluster travels slowly along the fallopian tube toward the uterus. Tiny hair-like structures lining the tube, along with gentle muscle contractions, move it along. The journey takes about three to four days.
By around the third or fourth day after fertilization, the embryo is a solid ball of 16 or so cells. Because it looks a little like a mulberry, it is called a morula, from the Latin word for that fruit.
Identical twins come from this early stage. If the cluster splits into two groups that each go on developing, two babies with the same genes result. This is a matter of chance, not family history, and happens in about 3 or 4 of every 1,000 births.
Your body is still running on its normal second-half-of-the-cycle hormones. Nothing yet signals that a pregnancy has started.
Try this: Go to bed a little earlier tonight. Good sleep habits now will serve you well in the tired weeks ahead.
Day 17 · 2 weeks 2 days
Keep caffeine under 200 mg a day
You do not need to give up coffee or tea, but it is wise to keep caffeine below 200 mg a day in pregnancy. Above that, studies link caffeine with a higher chance of miscarriage and lower birth weight. Caffeine crosses the placenta, and a baby clears it very slowly.
The tricky part is that caffeine content varies a lot. As a rough guide: a mug of brewed coffee: about 100 to 150 mg, sometimes more a single espresso: about 60 to 100 mg
- a mug of black or green tea: about 30 to 60 mg
- a can of cola: about 30 to 40 mg
- a small (250 ml) energy drink: about 80 mg
- a 50 g bar of dark chocolate: up to about 50 mg
Large coffee-shop drinks can contain well over 200 mg on their own, so size matters. Energy drinks are best avoided, as they often contain other stimulants and lots of sugar.
Decaffeinated coffee and tea contain only small amounts. Many herbal teas are caffeine-free, though not every herb is well studied in pregnancy, so stick to familiar ones such as peppermint or ginger in normal amounts. If you are used to a lot of caffeine, cut down gradually over a week or so to avoid withdrawal headaches.
Try this: Add up your caffeine for today, including tea, cola, and chocolate, and see how close you come to 200 mg.
Day 18 · 2 weeks 3 days
The ball of cells becomes a blastocyst
Around now, the cluster of cells reaches the uterus. Fluid seeps into the middle of the ball and it reshapes itself into a hollow sphere called a blastocyst. It is a small but important change, because the cells are now starting to take on different jobs.
An outer layer of cells, the trophoblast, forms the wall of the sphere. These cells will burrow into the lining of your uterus and go on to form most of the placenta. Inside, a small cluster called the inner cell mass gathers at one side. That cluster will become the embryo itself, along with the amniotic sac.
For a day or two, the blastocyst floats freely in the uterus. It is still wrapped in the protective outer shell that surrounded the egg. Before it can attach to the lining, it has to "hatch" out of that shell.
Your uterus is ready for it. Progesterone has made the lining thick, soft, and full of nutrients and blood vessels. This short period, when the lining is most receptive, is sometimes called the window of implantation. Try this: If you are taking a prenatal vitamin, check you have at least a month's supply left so you do not run out in the busy weeks ahead.
Day 19 · 2 weeks 4 days
The two-week wait can test your patience
If you are trying to conceive, the days between ovulation and a possible missed period are often called the two-week wait. Many people find it one of the hardest parts. You may catch yourself analyzing every twinge, every tired afternoon, every change in appetite.
Here is the honest truth: the hormones of the second half of a normal cycle cause many of the same feelings as early pregnancy. Breast tenderness, bloating, mild cramps, and moodiness are all common before a period. It is not yet possible to tell the difference by how you feel.
It can help to plan for the wait. Some people keep busy with work and friends. Others set a firm test date and promise themselves not to test before it. If you have been trying for a while, or have had a loss before, this time can bring up a lot. It is fine to say so.
You can live normally during the wait. Gentle exercise, work, and sex are all fine. Simply act as if you might be pregnant, which you have probably been doing already: no alcohol, no smoking, moderate caffeine, and folic acid every day.
Try this: Choose the date you will test, ideally on or after the day your period is due, and write it down so you are not tempted by each new morning.
Day 20 · 2 weeks 5 days
Hatching and attaching
About five or six days after fertilization, the blastocyst breaks free of its outer shell and comes into direct contact with the lining of your uterus. It usually settles in the upper part of the uterus, often on the back wall, where the blood supply is good.
At first, the attachment is loose. The blastocyst rolls and tumbles until the side with the inner cell mass lines up against the lining. Then the outer trophoblast cells begin to grip and press inward.
A remarkable conversation is happening. The blastocyst sends chemical signals to the lining, and the lining responds. The lining also becomes more tolerant of the blastocyst, which is genetically different from you. Without this, your immune system might treat it as foreign.
Not every fertilized egg gets this far. Many very early embryos stop developing before or during implantation, often because of chromosome differences that happen by chance at fertilization. When this happens, the next period comes on time or slightly late, and most people never know a pregnancy had started. This is a normal part of human reproduction, not something caused by anything you did.
For your partner: The wait is shared. Ask how your partner is feeling about it, and agree together on how you want to handle testing day.
Day 21 · 2 weeks 6 days
The blastocyst begins to burrow in
Implantation is under way. The outer trophoblast cells push into the lining of your uterus and begin to break down a small area of it, making room for the blastocyst to sink in. Over the next several days, it will become completely buried in the lining.
As it settles, the trophoblast starts to make a hormone called human chorionic gonadotropin, or hCG. This is the hormone pregnancy tests detect. Its first job is to tell the corpus luteum in your ovary to keep making progesterone. That stops your period from coming and keeps the lining in place.
At first, the amount of hCG is tiny. It takes several more days before there is enough in your blood, and then your urine, for a test to pick it up. Testing now will almost always give a negative result, even if you are pregnant.
The inner cell mass is also changing. It is starting to organize into two layers of cells, a flat disc that is the first true outline of the embryo. Every organ and tissue of your baby will grow from these cells.
Try this: Resist the test for a few more days. Put the box somewhere out of sight until your chosen date.