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Here's what you can expect during the different stages of pregnancy

12 min read

This article was last updated on June 3, 2021.

Pregnancy can be overwhelming, especially if it’s your first time. We compiled this guide meets pregnancy calendar to make navigating all three trimesters a little easier. We're outlining what to expect in each trimester, including noteworthy changes from week to week, and what's worth bringing up with your doctor. But since every pregnancy is unique, consider this a loose blueprint of what's to come.

Before we get into the details, let’s answer some common FAQs so you're informed about the big picture as soon as you know you’re pregnant (if you don’t already!):

  • How long is a standard pregnancy? A typical pregnancy lasts for 40 weeks, starting from the day of your last menstrual period (LMP) since that's easier to pinpoint than the exact time of conception. These 40 weeks are categorized into the first trimester (first day of LMP through 13 weeks and six days), the second trimester (14 through 27 weeks and six days), and the third trimester (28 through 40 weeks and six days).
  • How soon can you tell if you’re pregnant? The first sign of fertilization is typically a missed period, though that’s a difficult marker if you have irregular cycles or if you mistake implantation bleeding (more on this in a bit) for a menstrual cycle. You can use an early home pregnancy test to detect pregnancy a few days before your missed period. (The Modern Fertility Pregnancy Test can provide results six days prior.)
  • What’s the expected weight gain during pregnancy? Everybody is different. Your OB-GYN can provide a specific recommendation for weight gain based on your prepregnancy weight. On average, depending on your weight before conceiving, people typically gain anywhere from 11-40 lbs after 40 weeks of pregnancy.
  • When should you first reach out to your healthcare provider? You can call your OB-GYN as soon as you suspect you may be pregnant or get a positive pregnancy test, but they may not recommend coming into the office until about week 8.

Read on to learn all about fetal development, what your visits to the doctor may be like during different stages of pregnancy, and what you can be doing at home to stay proactive and feel your best all the way until your due date. You’ve got this!

What to expect during the first trimester

What's happening to your body

In the first trimester, you might start noticing these early signs of pregnancy:

  • Implantation bleeding (light bleeding that can sometimes occur when a fertilized egg finds a home in the uterus) may also occur, which is typically lighter and shorter than a regular period — however, some people mistake this for their period, and may not realize that they're pregnant until their next missed cycle.
  • Breast/chest tenderness
  • Nausea with or without vomiting (aka morning sickness)
  • Increased urination
  • Fatigue
  • Food cravings and aversions
  • Heartburn
  • Constipation

What's happening to the growing fetus

Weeks 4-8:

  • The fetal brain and spine (aka the neural tube) start forming
  • Cardiac tissue and the muscles of the eyes, nose, and mouth begin developing
  • Developing hands and feet will have webbed fingers and toes
  • Lungs begin forming the tubes that will carry air in and out after birth
  • The inner ear begins to develop

OB-GYN and Modern Fertility medical advisor Dr. Jenn Conti, MD, MS, MSc explains that the neural tube development that happens so early in pregnancy "is why it’s so important to get those prenatal vitamins on board ASAP — and ideally before you conceive." Starting prenatals after you're already pregnant might mean you've missed that crucial time for folate to support neurodevelopment.*

Weeks 9-12:

  • Cartilage for the limbs, hands, and feet start to form (but it won't harden into bones for a few weeks)
  • Eyelids form (but remain closed)
  • The genitals and liver begin to develop
  • Kidneys begin producing urine and the pancreas begins producing insulin
  • Fingernails begin to form

What to know about prenatal care

While the appointments you can expect during the first trimester are incredibly varied based on provider, clinic, and geographic location, there are typically two: one initially to confirm the dating and location of the pregnancy (typically around 6-9 weeks and another around 10-12 weeks to officially start prenatal care. At these appointments, you'll likely undergo the following tests and screenings:

Blood work: During the first trimester, blood tests are conducted to find out your blood type, check for vaccine antibodies (rubella and varicella), test for sexually transmitted infections (STIs), and measure A1C (to assess diabetes risk). (If any of the above was covered during your preconception appointment, you won’t need to do it again.)

Prenatal genetic screening tests:

  • Maternal serum analytes: These are blood tests done in the first and second trimesters that measure hormone levels in the pregnant person's blood (called analytes) to screen the fetus for certain genetic conditions. They're typically combined with the nuchal translucency (or NT) ultrasound below.
  • Noninvasive prenatal testing (NIPT): After 10 weeks, you'll also have the option to identify chromosomal abnormalities through a one-time blood sample with noninvasive prenatal testing (NIPT), sometimes called cell-free DNA testing. NIPT can also tell you sex assigned at birth and the fetus' blood type.

Carrier screening: These are blood tests done on the biological parents that determine whether a person carries a gene for certain inherited disorders. Carrier screening can be done before or during pregnancy. Commonly tested conditions include cystic fibrosis and spinal muscular atrophy.

Chorionic villus sampling (CVS): Between 10 and 13 weeks, fetal cells in a sample of chorionic villi (part of the placenta) can be tested for chromosomal abnormalities and any inherited disorders you're interested in testing for.


  • The first-trimester ultrasound: At your first appointment, your healthcare provider may confirm pregnancy via ultrasound, estimate gestational age (in conjunction with the first day of your last period, or LMP), check to make sure the pregnancy is developing in the uterus, see how many fetuses there are, and evaluate the fetal heart rate.
  • Nuchal translucency (NT) ultrasound: Between 11 and 13 weeks, you'll have a nuchal translucency (NT) ultrasound to test for chromosomal abnormalities.


  • The flu shot: This can be administered at any point during pregnancy and is highly recommended.
  • The COVID-19 vaccine: This can also be administered at any point during pregnancy and is fully supported by leading medical bodies for anyone who wants it. Read up on how we know the vaccine is safe during pregnancy here.

Steps you can take

There are lots of steps you can take to start prioritizing both you and your developing fetus' health:

  • Take a daily prenatal vitamin if you aren’t already (like Modern Fertility’s prenatal multi!) with at least 400 micrograms (mcg) of folate (aka methylfolate or folic acid).
  • If you’re taking any other medications, call the prescribing doctor to discuss pregnancy safety and whether or not you should discontinue use.
  • Stick to mocktails only and discontinue any smoking or vaping.
  • If you’re feeling nauseous, opt for bland foods and smaller portion sizes. Ginger (ginger ale, ginger tea, etc.) can help settle the stomach.
  • Pay attention to nutrition and exercise (which is recommended during pregnancy). You can find nutrition and exercise guidelines for pregnancy here and here, but keep in mind that everyone's bodies are different. Talk to your healthcare provider for personalized recs.
  • Drink lots of water. It helps with everything.

When to call your doctor

According to the Cleveland Clinic, here's what's worth calling your healthcare provider about in the first trimester (weeks 4-14):

  • A fever above 100.4 degrees Fahrenheit
  • Bleeding so heavy that you’re soaking an entire pad within an hour for three hours or more
  • Unusual and/or severe cramping or stomach pain
  • Excessive vomiting and/or diarrhea
  • Fainting spells
  • Pain or burning while peeing or trouble peeing
  • Unusual vaginal discharge
  • Swollen hands, fingers, or face (especially if one hand or finger is more swollen than the other)
  • Blurred vision or eye spots
  • Severe headaches
  • Pain or cramping in the arms, legs, or chest

What to expect during the second trimester

What's happening to your body

These physical changes could become more prominent during the second trimester:

  • A growing bump and larger breasts/chest
  • Darker skin around your nipples
  • Stretch marks on your stomach, breasts/chest, thighs, and buttocks
  • A dark line on your belly that stretches from your belly button to your pubic area (aka linea nigra)
  • Darker skin patches on your face, especially on your cheeks, nose, forehead, and/or upper lip (aka melasma)

While most of the early pregnancy symptoms (fatigue, breast tenderness, nausea and vomiting) begin to improve after the first trimester, nausea and vomiting will occasionally continue on through about 18 weeks. But these other common symptoms may take their place:

  • Wrist pain (carpal tunnel can get worse because of the increased swelling all over)
  • Heartburn
  • Constipation
  • Braxton Hicks contractions (mild, irregular contractions that typically happen in the afternoons, evenings, or after physical activity or sex — talk to your doctor if they happen more often or are painful as that might indicate preterm labor)
  • Nasal congestion and gum bleeding
  • Dizziness
  • Leg cramps
  • Vaginal discharge
  • Urinary tract infections (UTIs)

On vaginal discharge during the second trimester: "Leukorrhea is the medical term for the white-colored, normal discharge that increases throughout pregnancy," says Dr. Conti. "It’s annoying but serves an important purpose, which is to naturally flush away any bacteria that would try to ascend the cervix into the uterus, and protect that precious cargo!"

What's happening to the growing fetus

14-16 weeks:

  • Bones (especially the long ones) harden
  • Skin begins thickening
  • Toenails start to form
  • Necks will become defined and the lower limbs will develop
  • Hearing begins to develop
  • Lungs begin to develop a type of tissue that allows breathing after birth
  • You can start seeing the fetus make faces and gestures

17-20 weeks:

  • The fetal brain will be able to control motor movements
  • The digestive system begins working
  • You'll be able to identify ears, nose, and lips on an ultrasound
  • In fetuses assigned "female," the uterus and vagina will begin to form
  • Soft, downy hair all over the body (lanugo) will begin to develop

21-24 weeks:

  • Kicks and turns become stronger
  • The sucking reflex begins developing
  • Fat starts forming under their skin
  • The beginnings of finger and footprints form
  • The skin is wrinkly and visibly reddened by blood vessels

What to know about prenatal care

Expect prenatal appointments with your doctor every four weeks through the second trimester. At these appointments, the following things may happen:

Maternal serum analytes: The second part of the first- and second-trimester blood tests (together often called “the quad screen”) is done between 15 and 18 weeks to measure the levels of four hormones (alpha-fetoprotein, or AFP, or human chorionic gonadotropin, or hCG, estriol, and inhibin A) and detect chromosomal abnormalities. The results from screenings in the third trimester will be evaluated in combination with results from the second trimester for a full picture of the likelihood of chromosomal abnormalities.

Amniocentesis: After 15 weeks, fetal cells in a sample of amniotic fluid can be tested for the same things as CVS — with the addition of some neural tube (brain, spine, and spinal cord) defects.

A glucose challenge test: Between the 24th and 28th weeks of pregnancy, your blood sugar level will be measured by a blood test one hour after drinking a syrupy, glucose-filled solution to screen for gestational diabetes. An additional screening will be needed (measuring blood sugar levels after three hours) before diagnosis.


Steps you can take

While this trimester is typically when pregnant people feel their best (meaning more time for planning!), there are a few ways to manage any discomforts at this stage of pregnancy:

  • Natural fluid retention can cause carpal tunnel syndrome, so you may experience wrist pain and tingling in the hands and fingers. Sleeping in wrist splints can help relieve this issue.
  • For heartburn, avoiding fried, spicy, and fatty foods (as well as cutting back on portion sizes) can help. After a meal, make sure to stay standing or sitting upright for about 30 minutes, or risk having stomach acid come back up. If you’re still having trouble with heartburn, talk to your provider about appropriate over-the-counter medication management.
  • Water can help with constipation. If you’re still suffering from infrequent bowel movements, a stool softener like Colace (available over the counter) can be helpful.
  • If you’ve got a case of puffy feet, kick your feet up whenever you’ve got a chance. Compression stockings can also be helpful in reducing swelling, as well as cutting back on salt intake. As always, keep drinking that water! If the swelling is noticeable in the legs or face, let your provider know.

When to call your doctor

In the second trimester (weeks 14-27), here's when to call your doctor (according to the Cleveland Clinic):

  • Unusual and/or severe cramping or stomach pain
  • Noticeable changes in fetal movement after 28 weeks (like fewer than 6-10 movements in one hour or less)
  • Worsening difficulty breathing or shortness of breath, headache unrelieved by acetaminophen, new vision changes, or pain in your mid-upper/right-upper abdomen (all potential symptoms of a condition called preeclampsia that can develop after 20 weeks)
  • Signs of premature labor (i.e., regular tightening or pain in the lower stomach or back, any bleeding in the second trimester, fluid leakage, or vaginal or pelvic pressure)

What to expect in the third trimester

You're in the home stretch! By 37 weeks, your pregnancy is considered early term (i.e., no longer preterm) and by 39 weeks, full term. (Note: The language surrounding this changed relatively recently, but pre- and not-preterm are still the same.) In the last few weeks of your pregnancy, your body may go through these changes:

At the same time, you may experiences these symptoms:

  • Braxton Hicks contractions
  • Backaches
  • Shortness of breath
  • Heartburn
  • Spider veins and varicose veins
  • Hemorrhoids
  • Frequent urination
  • Trouble falling or staying asleep
  • Leaking breasts/chests (with colostrum, a watery pre-milk substance)
  • Mood swings

In regards to the last bullet (mood swings), Dr. Conti adds: "'Postpartum depression' is a misnomer. Anxiety and depression can happen at any time during and after pregnancy."

What's happening to the growing fetus

25-28 weeks:

  • The lungs are fully formed but can't yet function outside of the uterus
  • The lungs also begin to produce surfactant (a substance needed for breathing)
  • The fetus can respond to loud noises with their movements
  • Their eyelids can open and close
  • The fetal nervous system begins developing
  • Increased fat levels make the skin look smoother

29-32 weeks:

  • Stretching, kicking, and grasping motions are all possible
  • The eyes begin sensing changes in light
  • The bone marrow begins forming red blood cells
  • There may be some head hair (but no more lanugo)
  • In fetuses assigned "male," the testicles will begin to descend

33-36 weeks:

  • Bones begin to harden but the skull stays soft and flexible
  • Fingernails have grown to the fingertips
  • Limbs will begin to look chubbier
  • There may be movement to the head-down position for birth

37-40 weeks:

  • The circulatory system, musculoskeletal system, nervous system, lungs, and brain are done developing
  • Fat levels will continue increasing

What to know about prenatal care

In the third trimester, you'll go from biweekly or monthly appointments (depending on the circumstances of your pregnancy) with your doctor to weekly ones after 36 weeks. Here's what may happen at those appointments:

A group B strep swab: This is a rectal-vaginal swab used to check for the presence of group B strep, a common and native bacterial strain, in the vagina. Some people have it, some don't — but if you test positive, antibiotics will be administered in labor to prevent transmission to the infant.

Ultrasounds: Toward the end of your pregnancy, your doctor may check the position of the fetus, with the assistance of an ultrasound, to make sure it's in the right placement for birth and delivery.

The Tdap vaccine: This vaccine for the whooping cough is recommended once in the third trimester.

Blood work: Additional lab work may be done, depending on your provider.

Steps you can take

  • Rest, and get comfortable (with lots of pillows!) while doing so. Pregnancy support belts (or a “belly band,” an elastic band that helps to lift the belly), kinesiology tape, swimming (no gravity!), and massage can all help alleviate typical aches and pains.
  • Drinking water is especially good for Braxton Hicks contractions, as they can often be caused by dehydration.
  • Make sure you’ve got the things you’ll need at home, like a breast pump and a car seat. Breast pumps are often covered by insurance with a written prescription, so bring this up to your provider.
  • Rest and enjoy one-on-one time with your partner if you have one or solo time for yourself.

When to call your doctor

During the third trimester (weeks 28-40), it's important to reach out to your healthcare provider if one of the following things happen:

  • Any signs or symptoms that don't feel normal
  • Any vaginal bleeding
  • Increased vaginal discharge with an odor
  • Fever, chills, or pain when peeing
  • Headaches
  • Changes or blind spots in your vision
  • Your water breaks
  • Regular, painful contractions
  • A decrease in fetal movement
  • Significant swelling and weight gain.
  • Chest pain or difficulty breathing

While this pregnancy calendar will hopefully help quell some of your uncertainties, your provider is your best source of info throughout your pregnancy. Write any questions down as they come to mind so you'll have them on hand at visits, and share your questions in the #first-trimester channel with other parents-to-be in the Modern Community.

Pregnancy is different for everyone who experiences it — but information and support (from your provider, friends, and Modern Community members alike) can help you feel as prepared as you can be for what comes next.

This article was reviewed by Dr. Jennifer Conti, MD, MS, MSc.

*This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

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Rachel Sanoff

Rachel Sanoff is a writer and editor in Los Angeles. She was previously an essays editor at O.school, a digital sex education platform, and the features editor at HelloGiggles.

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