What to Expect in the First Trimester of Pregnancy
After months of circling your ovulation days on the calendar and purchasing pregnancy test after pregnancy test (the cashier at the pharmacy knows you by name now), you finally get the test result you’ve been waiting for—you’re finally pregnant.
Congratulations! You’re about to enter those crucial first months of pregnancy—a.k.a., your first trimester.
Understanding what to expect in the first trimester, what to expect in the second trimester, and what to expect in the third trimester can ease the journey and give a better understanding of what's happening. The first trimester comes with a ton of physical and emotional transformations. After all, your body is preparing to create a human life! To stay calm through this sea of change, you should know what’s on the horizon. From hormones to heartburn, let’s explore what to expect in the first trimester.
Trimesters: Your Pregnancy in Three Acts
At this point you might be wondering, what exactly is a trimester? Essentially, medical professionals divide your nine month pregnancy into three acts, otherwise known as your trimesters.
Each trimester consists of about three months (hence the term “tri”), but the weekly breakdown looks like this:
- First Trimester – 0 to 13 weeks
- Second Trimester – 14 to 26 weeks
- Third Trimester – 27 to 40 weeks
Not everyone’s pregnancy follows this exact structure—or even the typical nine month duration. A little variance is totally normal.
However, it’s important to note that your first trimester technically starts from the moment of conception (when a sperm cell fertilizes your egg), not your first missed period, as your body starts undergoing changes immediately after this moment.
After conception, your entire body shifts gears into baby-making-mode. Because everybody is unique, these changes might look a little different from woman-to-woman.
Here’s a broad view of all the physical changes you can expect during your first trimester.
If pregnancy is a road trip, hormones are the gas. No healthy pregnancy is complete without a few major hormonal shifts. And lucky for you, your first trimester carries the bulk of these chemical changes.
Right after conception, the following hormones catapult into action to prepare your body for baby:
- Human chorionic gonadotropin (hCG) – A hormone exclusive to pregnancy, hCG is the hormone that pregnancy tests look for when determining whether you’ve got a bun in your oven. This important hormone helps your body prepare for a growing baby by triggering other hormones to rise. From conception, hCG levels double every few weeks until they peak around 8 to 11 weeks. Unfortunately, hCG is also thought to be the hormone that causes morning sickness during the first trimester.
- Progesterone – Triggered by rising hCG levels, progesterone levels increase to help relax the uterus and make it a more hospitable environment. However, this early progesterone spike also comes with PMS-like symptoms, like mood swings, acne, and constipation (yay, pregnancy!).
- Estrogen – Known as the “female” hormone, rising estrogen levels in the first trimester help to regulate progesterone levels and increase blood flow to support your growing baby. Boosted estrogen can also give that signature “pregnancy glow” to your skin. However, the elevated blood flow may cause symptoms like a stuffy nose and frequent urination.
- Human placental lactogen (hPL) – Around week three, the placenta forms and begins releasing hPL. This hormone boosts the placenta’s ability to nourish your baby by breaking down your food’s macronutrients and decreasing insulin resistance.
These are just the starting players on your pregnancy bench. The above hormones trigger a cascade of other hormones that protect and boost fetal growth. These can include:
- Calcitonin – In charge of bone formation
- Relaxin – Which promotes relaxation of uterine, pelvic, and other muscles
- Erythropoietin – Which boosts red blood cell production
- Corticotropin-releasing hormone – Responsible for pregnancy duration regulation
- Thyroid-stimulating hormone – A key player in metabolism support
While every pregnant woman experiences hormone increases during the first trimester, physically, these hormones can manifest differently.
The most common physical changes that occur during these first few months include:
- Breast tenderness – Shifts in progesterone and estrogen levels create breast tenderness, which usually lasts until the second trimester.
- Fatigue – During pregnancy, your body is working overtime to support you and your little guy or girl. You’ll likely experience bouts of fatigue or tire more easily during the day, so make sure you give yourself time to relax. After all, creating a human life is no easy task.
- Weight gain – Gaining weight isn’t just suggested during pregnancy—it’s crucial. Without weight gain, your baby won’t grow to their full, healthy size. However, don’t push yourself. Medical professionals recommend gaining about 2 to 4 pounds during the first trimester. The bulk of your weight gain will come later in your pregnancy.
- Skin changes – Thanks to rising estrogen levels, pregnancy can deliver downright glowy skin. However, acne-prone women should watch out for excess sebum or facial oil production. Similarly, melanin (natural skin pigmentation) increases during pregnancy, which can potentially create dark spots. Fortunately, most of these dark spots will fade after your pregnancy.
Another significant change you’ll experience during your first trimester? Your digestion.
In fact, the majority of women experience digestive issues during the first few months of pregnancy. These issues can include:
- Constipation – Thanks to rising progesterone, constipation is common during the first trimester. Progesterone not only relaxes the uterine muscles, but also the muscles that help food move through the digestive system. Additionally, prenatal iron supplements can trigger constipation. To help combat this symptom, make sure you’re drinking plenty of water throughout the day and eating a diet rich in fiber and whole grains. You can also talk to your doctor about taking a probiotic supplement.
- Nausea & morning sickness – Rising hCG and progesterone levels can trigger nausea, stomach aches, and vomiting during the first three months of pregnancy. Perhaps the most troublesome early pregnancy symptoms, nausea and morning sickness affect up to 85% of pregnant women. If you’re struggling with this symptom, try sipping on ginger tea or eating smaller meals throughout the day. While morning sickness is normal during pregnancy, excess vomiting should be treated by a medical professional.
- Heartburn (acid reflux) – While less common during the first trimester, heartburn results from progesterone relaxing the lower esophagus sphincter. As a result, stomach acid can flow upwards and create a burning sensation or pressure. Taking over-the-counter antacids and eating smaller meals can help quell this first trimester common symptom.
Yes, your menstrual period will go incognito for about nine months, but that doesn’t mean your entire pelvic area is checking out. During the first trimester, you’ll likely see a few of the following early pregnancy symptoms around the vaginal area:
- Bleeding or spotting – We know—seeing that red stain is downright scary during pregnancy. But, if you see blood, don’t freak out. Spotting is absolutely normal during the first trimester. In fact, up to 25% of women experience implantation bleeding at some point during the first few weeks of pregnancy, triggered by the fertilized egg implanting into the uterine lining.
- Discharge – Just like during non-pregnant times, it’s normal to see white discharge during pregnancy. However, it’s important to make sure this discharge isn’t green or yellow and doesn’t have a particularly strong smell, as this signals an infection.
- Increased urination – It’s not technically a vaginal symptom, but as your uterus grows during the first trimester, your bladder gets a little smushed. Translation? You’ll likely be running to the bathroom more often.
Emotional & Mental Changes
During pregnancy, all of these hormonal changes bring emotional and mental symptoms along for the ride. Whether it’s the baby blues or a new craving, here’s a few inner shifts that might happen during the first trimester:
- Taste preferences – Pickles and peanut butter? Chocolate-covered cheese? Many newly pregnant women develop intense desires or dislikes for certain foods. Some might even develop dysgeusia, or a decrease in taste. Changes in smell often accompany these taste fluctuations.
- Mood swings – Just like during menstruation, hormonal shifts during pregnancy can open the gates to intense moods. Rising progesterone in particular can trigger anxiety, depression, insomnia, or other negative emotions. While experiencing these mood swings is normal, it’s best to have a support system nearby to help you handle the ups and downs. Pregnancy hormones are normal but should be observed for any abnormal hormonal changes.
- Symptom fatigue – Dealing with nausea, discharge, and a growing body can be, well, exhausting. Symptom fatigue is common during pregnancy, especially the first time around. Wrap yourself up in our pregnancy robe for ample rest and be open to receiving the support from loved ones during these initial few months.
At the end of the day, all of these first trimester changes are worth it because they’re leading to the most important thing—your baby. And, in fact, your baby is also going through first trimester changes!
During the first few months, your baby takes some extraordinary steps in growth. Here’s a general outline of what happens in the first trimester of baby-making.
Weeks 1 to 4
After fertilization, your egg has one job: implantation into the uterine lining. Once implanted, your egg can begin the process of growing into an embryo.
After implantation, the embryo first splits into two parts—the eventual fetus and the placenta. This rice grain-sized embryo then starts forming tiny signs of humanhood, including:
- Neural tube (the eventual brain and spinal cord)
- Eyes and ears
- Miniature limbs
- Heart and heartbeat
Weeks 5 to 8
From bones to brain, the second month is all about continued growth. All of these gradual physical changes help your baby start to take on a human form:
- Major organ system developments (circulatory, digestive, urinary, etc.)
- Head development
- Tooth buds
- Distinct limbs
- Detectable heartbeat
- Bone development
Weeks 9 to 13
At this stage, your embryo has transformed into a fetus. While just an inch or two long, the majority of its major organs have formed (and you just might feel the first kick). Now, the physical details start to form, such as:
- Fully-formed limbs
- Vocal box
- Genital organs
Monica + Andy: Baby Gifts and Classes For Your Greatest Gift of All
The first trimester of pregnancy can be a tumultuous time, filled with excitement and anticipation, as well as nausea and sore breasts. But no matter what the first trimester brings, you can find joy in the fact that you’re on the path to meeting your newest family member.
During your pregnancy journey, you can learn even more about your growing boy or girl by joining the Monica + Andy parent community. Our virtual and in-person classes offer tips, advice, and support for everything from newborn sleep schedules to prenatal yoga. Prepare for your pregnancy and everything to come, with Monica + Andy.
- University of California-San Francisco. Pregnancy: The Three Trimesters. https://www.ucsfhealth.org/conditions/pregnancy/trimesters
- Today’s Parents. How pregnancy hormones affect your body in each trimester. https://www.todaysparent.com/pregnancy/pregnancy-health/how-pregnancy-hormones-affect-your-body-in-each-trimester
- Healthline. Human Placental Lactogen: Function During Pregnancy, Test, Results. https://www.healthline.com/health/human-placental-lactogen
- What to Expect. Pregnancy Hormones Guide: Estrogen, Progesterone & More. https://www.whattoexpect.com/pregnancy/pregnancy-health/pregnancy-hormones.aspx
- MedlinePlus. Managing your weight gain during pregnancy. https://medlineplus.gov/ency/patientinstructions/000603.htm
- Stanford Children’s Hospital. Pregnancy and Skin Changes. https://www.stanfordchildrens.org/en/topic/default?id=pregnancy-and-skin-changes-134-7
- WebMD. First Trimester of Pregnancy: What to Expect, Baby Development. https://www.webmd.com/baby/guide/first-trimester-of-pregnancy
- American Pregnancy Association. Baby Development Month By Month | American Pregnancy Association. https://americanpregnancy.org/healthy-pregnancy/week-by-week/baby-development-month-by-month/