About six days after fertilization, the blastocyst has planted into your uterine wall. The inner cell mass, or embryoblast, has grown into a disk-like structure, two cell layers thick: the epiblast, which forms the amniotic cavity (the closed sac between the amniotic fluid and embryo); and the hypoblast, which forms a tiny yolk sac. In these early weeks, the yolk sac provides nourishment to the embryo until your placenta is fully formed.

The outer cell mass, or trophoblast, is becoming a large part of the placenta. But for now, your primitive version of the placenta is working hard to create space in the lining of your uterus, allowing your blood to flow and helping you provide your little one with oxygen and nutrients as he or she grows.

PS. Your baby's neural tube is beginning to develop.And yes, it's totally normal to brag about growing neural tubes.

Do you feel pregnant? Chances are, you do! Mood swings, intense smells... everyone is different. You may feel more fatigued than usual, or a little nausea. Some women experience tender nipples and swollen breasts. And some women feel no symptomatic difference whatsoever during the fourth week.

It's time to find out.

You'll get the most accurate result on your home pregnancy test at the end of this week. Some women are lucky enough to find out as soon as they've missed their period, and others won't find out until week five. Name-brand and generic home pregnancy tests are equally sensitive and frequently stubborn about detecting the hCG hormone in your urine during the fourth week. If your test is negative, wait until week five and take another test.

If your home pregnancy test detects enough of the hormone hCG in your urine this week, you'll see that glorious positive result. Even if you discover a very faint - but still positive - test result, there's a great chance you’re pregnant. And yes, it's normal to wonder if you eyeballed the fabulously lowkey, faint result into existence or truly see it (feel free to use the buddy system if you really aren't sure), and it's equally as normal to take multiple tests (just to be extra sure).

Whether your home pregnancy test result is clearly positive or only just, you should contact your doctor, midwife, doula, or other healthcare practitioner to schedule your first prenatal appointment. You should also ask if the vitamin supplements, prescriptions, and/or over-the-counter medications you're taking are safe to continue.

Be mindful of what you put into your body during these early weeks, when your little one is most vulnerable. The first trimester is the most critical, susceptible stage in your baby's formation and development. You should avoid alcohol, drugs, cigarettes, secondhand smoke, and certain medications.