Pregnancy Week 1: A Guide to What’s Happening Inside Your Body When You’re 1 Week Pregnant

Pregnancy Week By Week

Getting a week by week update is a really fun way to stay informed and celebrate every cute little milestone during your pregnancy—from the very first week all the way to the very last. But the most interesting fact about pregnancy so early on, is that in week 1, there’s not even a baby yet. That’s right! You’re not actually pregnant at all.

So, why is this part of your cycle labeled as a week of pregnancy in the first place? Shouldn’t you just start counting weeks once you’re actually pregnant? It seems logical, right?

To make sense of it all, let’s take a look at what’s happening inside your body during that very important week. Then, we’ll discuss why doctors consider this time period to be the first official week of pregnancy even though you and your partner haven’t made a baby just yet.

Pregnancy Week 1

Strangely enough, the beginning of your pregnancy is calculated by determining the first day of your last period. In other words, the first week of pregnancy is the exact same week your most recent menstrual cycle began. And this is the time when your body starts shedding all of the blood and built-up uterine lining from your uterus out through your cervix and vagina.

Even though fertilization did not occur during the past month, which in turn, caused your period to start, your body is preparing itself for another round of ovulation even now. And, if all goes well, an egg and a sperm will join up together in one of your fallopian tubes, resulting in conception sometime by the end of week 2 of your pregnancy.

So, even though you’re technically not pregnant yet in the first week, your body’s already trying to conceive a baby for you during week 1 and 2 of your cycle. In essence, your last menstrual period isn’t just an ending, it’s also a new beginning.

And that’s because, when your menstrual period starts, your body releases a hormone called follicle stimulating hormone. This hormone causes some of the eggs inside your ovaries to start preparing themselves for the next ovulation cycle. Eventually, one of these eggs, sometimes more than one, will become the dominant egg—which will then be released into one of the fallopian tubes the next time you ovulate. 

Remember, at this point, taking a home pregnancy test would definitely give you a negative result. Because, again, you haven’t made the baby with your partner just yet. But that is about to happen very soon during the 2nd week of your pregnancy.

Early Signs of Pregnancy

At 1 and 2 weeks pregnant, you will not notice any early pregnancy signs like having a missed period, swelling of your breasts, bloating, or frequent urination. And that’s thanks in large part to the fact that you’re not actually pregnant yet.

Soon enough, you’ll start noticing the early signs of pregnancy. And while this is likely to be one of the most exciting periods of your life, those early signs can be a little hard to get used to. So, talk to your doctor as often as you need to—sharing your honest thoughts and feelings about this stage of your pregnancy and getting answers to all the questions currently on your mind.

Pregnancy Symptoms

While you’re most likely experiencing the uncomfortable, and sometimes painful, symptoms as a result of having your period during this time, you are not experiencing any pregnancy symptoms at all. So, while symptoms like nausea, breast tenderness, mood changes, and fatigue are surely coming soon, they aren’t here quite yet.

Each pregnancy is entirely different, but most women report having at least a few of these common symptoms which leave them feeling anything but good. So, ask your doctor to see what you can do to lessen the less-than-desirable effects of pregnancy in the safest and healthiest way possible.

Pregnant Belly at 1 Week

A cute little pregnant belly is still a ways off during the first week of pregnancy. Since there’s no baby growing inside of you yet, you will not experience any change in weight or belly shape as a result of pregnancy during this time.

Of course, bloating is one of the more common menstrual symptoms, so your belly may look a little swollen now at this time. But, an actual pregnant belly is most likely to appear between weeks 16 to 20. Again, this timeframe can differ slightly based on your particular circumstances.

Baby at Week 1

Sadly, since a baby hasn’t been conceived yet, it’s far too early to track its development. Your body is preparing itself to become pregnant soon, but it will take another couple of weeks until a baby has officially been made. Once that happens, you can start reading up on baby development in general as well as the weekly progress your little one is making right now.

Since you’re trying to get pregnant soon, it’s always a good idea to start making lifestyle changes now so that you can increase your chances of having a healthy pregnancy later on. Doing things like getting plenty of rest, staying hydrated, and taking prenatal vitamins are all great ways to have a higher chance of delivering a healthy baby.  

40 Weeks Pregnant

Now that you know that pregnancy is calculated from the first day of your last menstrual cycle, you may be wondering why that is. And there’s a simple answer to that question.

Determining the exact day conception took place is a pretty difficult process. So, to make it easier on your doctor, the 40-week pregnancy calendar starts on the first day of your last period—instead of when the fertilized egg officially came into being.

Therefore, your due date will be calculated based on the important determining factor of your last period and not when the sperm and egg actually met. Because, frankly, your doctor may not know.