1 month pregnant: Development and what to expect

You’re unlikely to know for certain whether you're pregnant in the 1st month, as most pregnancy tests are accurate after the first day of a missed period. This uncertainty can be all consuming, whether you’re trying for a baby or not. You might find yourself overanalyzing whether you feel any different. 

While we can’t predict the future, we can help you get clued up on some of the pregnancy signs to look out for. So let’s break down how a pregnancy could be developing at this stage, with advice from Flo expert Dr. Renita White, obstetrician and gynecologist, Georgia Obstetrics and Gynecology, Georgia, US. 

And if, when the time comes, you get a positive pregnancy test result, you can learn more with a pregnancy-tracking app like Flo. With weekly updates, Flo can help you stay informed, supported, and prepared for what’s next on your pregnancy journey. 

Key takeaways

• Your pregnancy is counted from the first day of your last period, even though you technically become pregnant during the second half of the month. 
• An average menstrual cycle is 28 days, but we’re all different. If your cycle is between 21 and 35 days, then it’s still considered normal. Throughout this piece, we will use a 28-day cycle as a benchmark for milestones in the pregnancy journey, but just know that they may slightly differ for you depending on your cycle length. You can learn more about how long your cycle is using an app like Flo. 
• Around day 14 of a typical 28-day cycle, your body releases an egg. This is known as ovulation. You become pregnant when this egg gets fertilized by a sperm and successfully implants into your uterus. 
• Most pregnancy tests are accurate after the first day of a missed period. However, there’s a chance you might notice some early pregnancy symptoms before that. Here’s what to look out for. 

Fetal development between weeks 1 and 4 of pregnancy

A lot is going on in your body during the 1st month of pregnancy. It’s in this month that a single cell (your fertilized egg) rapidly divides to eventually develop into your baby as well as the placenta, a whole new organ that keeps your baby alive.

“During this time, the fertilized embryo implants into the uterine wall and begins to develop,” says Dr. White. “The spine and brain begin to develop as well as the early amniotic sac [a cushiony layer that surrounds your baby to protect them in your uterus] and umbilical cord [the structure that passes food and oxygen from your body to your baby].” 

But, she adds, “In the first month of pregnancy, you generally don’t know you’re pregnant yet.” In fact, for at least the first 2 weeks of pregnancy, you’re not actually pregnant at all. How does that work? We’ll explain. 

How pregnancy weeks are counted can be a little confusing at first. Your gestational age (the age of your pregnancy) is counted from the first day of your last period, or day one of your menstrual cycle. However, you don’t technically become pregnant until a fertilized egg has implanted into your uterus, which can happen between days 20 to 24 of a typical 28-day menstrual cycle. So this means you’re not technically pregnant until the beginning of pregnancy week 4. 

This might feel confusing, but it’s standard practice for doctors to count pregnancy in this way. 

“Because it is not possible to know exactly when the egg was fertilized with sperm, an estimated due date is based on the first day of the last period,” says Dr. White. “With this dating system, we estimate that pregnancy lasts 40 weeks. The first two weeks technically account for the two weeks before ovulation.”

But while you’re not actually pregnant in weeks 1 and 2, some pretty major things are happening in your body to make an upcoming pregnancy possible. Let’s take a look at those in more detail. And remember, while a 28-day cycle is the average, yours might slightly differ, meaning the following events might happen at slightly different times for you. That’s typical, and you can use an app like Flo to better understand your cycle. 

Week 1: Your period

So at 1 week pregnant, you’ll have your period and be at the start of a new menstrual cycle. Your period is when the lining of your uterus sheds through your vagina, thanks to a drop in the hormones estrogen and progesterone. This makes way for a new lining to later grow and thicken, ready to support a possible future pregnancy. 

For most people, the bleeding lasts between two to seven days. During this time your body starts producing another hormone called follicle-stimulating hormone (FSH). FSH causes the small fluid-filled sacs in your ovaries (known as follicles) to grow and develop. Each follicle contains an egg, and when one is matured and ready, it will be released during ovulation. 

Week 2: Ovulation

At around 2 weeks pregnant, one of your developing follicles will form a fully mature egg. Then, around day 14 of a typical 28-day cycle, your body releases a sudden surge of luteinizing hormone, which causes your ovary to release the egg. This event — known as ovulation — is important, as now sperm have the chance to meet your egg and fertilize it. Depending on the length of your cycle, ovulation can happen at different times. 

So how can you tell when you’re ovulating? One way to know is by taking an at-home ovulation test, which involves measuring luteinizing hormone by peeing on a stick. The Flo app can also help you know where you are in your cycle by tracking your period dates. 

Then there are the following ovulation signs to look out for, although not everyone will experience these. 

• Wet, slippery vaginal discharge that looks a bit like raw egg whites
• A slight increase in your basal body temperature (your temperature when your body is at rest) after ovulation

Other people also report feeling: 

• Abdominal or ovulation pain
• Spotting or light ovulation bleeding
• Bloating

Week 3: Fertilization

After being released, your egg will live for 12 to 24 hours. During this time, it travels through one of your fallopian tubes where a sperm can meet and fertilize it. This is the milestone event known as conception.  

A quick side note if you’re trying to conceive: When you’re trying for a baby, this 24-hour window might seem impossibly small. But sperm can live inside you for up to five days, so by having sex regularly from three to four days before ovulation and up to one day after, you can maximize your chance of conceiving. 

At 3 weeks pregnant, once a sperm has fertilized your egg, it becomes a one-cell entity known as a zygote. This zygote contains all the chromosomes (thread-like structures that contain DNA) that will help determine your baby’s sex and physical characteristics. Half of the chromosomes come from you, and the other half, from your partner.

The zygote starts to rapidly divide as it travels down your fallopian tube to reach its final destination: your uterus. 

Week 4: Implantation

Roughly six to 10 days after ovulation, your fertilized egg (which has now grown to form a cluster of around 100 cells called a blastocyst) attaches itself to the lining of your uterus. This is known as implantation and is the moment when you officially become pregnant. 

It’s at this point that your placenta starts to form, plus the amniotic sac. The neural tube also starts to develop, which will one day become your baby’s brain, spine, and central nervous system. 

Despite all these changes, a pregnancy test won’t be able to detect that you’re expecting at this stage of the 1st trimester. We’ll explain. Initially after implantation, your embryo starts to release the pregnancy hormone human chorionic gonadotropin (hCG). As the placenta forms, this new organ takes over hCG production. HCG is the hormone that at-home pregnancy tests look for in your urine. 

However, it takes time for hCG to build up in your body to a level that’s high enough to be detected. These levels are often not high enough at 4 weeks pregnant. So, waiting to take an at-home pregnancy test until the first day after a missed period will reduce your chances of getting a false-negative result. 

If this wait feels tortuous, you’re not alone. Not knowing if you’re pregnant can be hard. It’s one of the most life-changing things that can happen to you, after all. It’s understandable if you’re constantly monitoring your body for signs. So let’s take a look at whether you can experience any symptoms of pregnancy at 1 month.

Symptoms you might experience when 1 month pregnant

One of the first pregnancy symptoms you might experience is a missed period, which may happen around 4 weeks pregnant if you have a typical 28-day cycle. But you may also experience very early pregnancy symptoms at the start of the 1st trimester. 

“Early pregnancy symptoms vary for everybody,” says Dr. White. “Some people experience symptoms, and others don’t.” So if you’re trying for a baby, and you haven’t noticed any changes, try not to get disheartened.

Dr. White adds, “It’s also possible that you won’t realize the symptoms you are having are due to pregnancy since it’s so early. Pregnancy symptoms in this period can often mimic premenstrual symptoms. For example, it is common to experience breast tenderness, bloating, light cramping, and fatigue.” 

Let’s look at those symptoms and others in more detail. 

Tender breasts

Hormonal changes can make your breasts feel tender, swollen, and sometimes sore soon after you get pregnant. 

Implantation bleeding

When the fertilized egg implants into the lining of your uterus, it can cause light bleeding or spotting. Known as implantation bleeding, this can happen one to two weeks after fertilization. This can be around the same time you’d expect to get your next period, which is why some people mistake the bleeding for their period arriving and falsely believe they’re not pregnant. To help you tell the difference, know that implantation bleeding is very light and can look just like a few small drops of blood or a brown-colored discharge. 

Implantation cramps 

Another possible implantation symptom is cramping. Implantation cramps should be very mild and not feel as painful as regular period cramps. 

Bloating 

The hormonal changes in early pregnancy can leave you feeling bloated, a bit like how you might feel at the start of your period. 

Nausea and vomiting

You’ve probably heard of the term “morning sickness,” but nausea (with or without vomiting) can happen at any time of day when you’re pregnant. This symptom can start as early as 4 weeks into your pregnancy and can be tough to deal with, especially if you’re choosing to keep your pregnancy secret at first. Eating small amounts regularly so that your stomach never gets fully empty can help manage nausea. Speaking to your doctor is also a good idea if you’re struggling. 

Fatigue

Some people feel more tired as early as one week after conception. A sharp rise in the hormone progesterone can be the culprit behind pregnancy fatigue. Your body is also having to pump more blood to your placenta and growing fetus. If you’re feeling more tired than usual, then make sure you give yourself the time and space to take things easy. 

Taking the first steps of your pregnancy journey

You may not suspect you’re pregnant until toward the end of the first month when you have a missed period. The only way to know for sure is by taking a pregnancy test. Remember, it’s best to take a test after the first day of your missed period. If you’re not sure when that is, Flo’s pregnancy test calculator can help you figure out when the best time to test might be. 

Getting a positive pregnancy test result can be a moment of mixed feelings, even if you’ve been trying to conceive. Lots of people feel happy but overwhelmed by what’s to come. It might help to know what you can do next. 

One of the first things you can do is let a health care professional know you’re pregnant so they can schedule your prenatal health appointments. Make a note of any questions you have before the call. For example, you might want to chat with them about the lifestyle changes you’ll need to make during pregnancy. For example, it’s a good idea to start taking folic acid and other prenatal vitamins if you haven’t already. “It is also important to avoid foods, medications, and toxins that can negatively impact pregnancy,” says Dr. White. “This includes avoiding tobacco, too much caffeine, and certain over-the-counter pain medications.” Your doctor will be able to explain all of this to you. 

You can also start tracking your pregnancy week by week, which is a great way to learn about the changes happening to your body. The Flo app can give you all the key information on the development of your pregnancy week by week, helping you to understand your symptoms and get advice on how to manage them.