Pregnancy Basics

Pregnancy by trimester


Fertilization, the union of the egg and the sperm into a single cell called a zygote, occurs in the fallopian tube. During the following days, the single cell divides into more cells and migrates to the uterus, where it implants. After implantation, the fertilized egg is called an embryo, and at the ninth week, it is called a fetus

Conception normally happens roughly 11-21 days after the first day of the last period (1). Pregnancy starts on the first day of a woman’s last period, lasts for roughly 40 weeks, and is broken into three trimesters.

The first trimester

Weeks 1 – 13

What’s happening?

During the first trimester, the uterus is supporting the beginning stages of growth in the fetus and placenta (1). The body is carrying nutrients and oxygen to the fetus. By the end of the first trimester, the baby will have all of their major organs, although they are not developed enough to function outside of the womb. 

During the first trimester, the following occur (2):

  • Your baby has arms, hands, legs, and feet by 6 weeks
  • Your baby is able to move their limbs by 8 weeks
  • Your baby’s intestines begin forming at 8 weeks
  • Your baby will start forming touch receptors
  • Your baby’s optic nerves, retina, and lenses will all form
  • The tube that will become the baby’s heart begins to beat spontaneously
  • Your baby’s skin begins forming around weeks 5-8
  • Your baby’s vocal cords are formed
  • Your baby’s white blood cells are formed to fight off illness
  • Your baby’s muscles are formed

Important notes

Because of the immense fetal growth that occurs during the first trimester, it is recommended that the mother begins taking prenatal vitamins before pregnancy, or as soon as possible during pregnancy (1). She should also maintain a healthy diet and schedule her first prenatal appointment 6-8 weeks after her last menstrual period.

First trimester maternal physical changes

Physical changes that may occur during the first trimester include (1):

  • Nausea
  • Fatigue
  • Breast tenderness
  • Mood swings
  • Headaches
  • Constipation

The second trimester

Weeks 14-27

What’s happening?

During the second trimester, the baby will be able to hear and recognize their mother’s voice. Their movements will also grow more noticeable to the mother. Most women feel their babies kicking at roughly 20 weeks.

During the second trimester, the following occur (3):


  • You should be able to hear the baby’s heartbeat with a stethoscope by 20 weeks, and the baby’s brain is now regulating that heartbeat. 
  • Your baby’s brain will be producing blinks, regulating heartbeat, and initiating kicking movements.
  • Your baby’s skin will acquire a vernix caseosa by week 19, which is a layer of oil and skin cells that protects the skin from amniotic fluid.
  • Your baby is growing hair by week 16 and has eyelashes and eyebrows by week 22. Their skin is covered in a layer of hair called lanugo. 
  • Your baby’s eyes are beginning to open and they are able to see, hear, and smell during the second trimester.
  • Your baby is sucking, swallowing, and tasting foods you eat via amniotic fluid (the fluid inside the uterus).

Important notes

Between 18-22 weeks, an anatomy ultrasound usually occurs, wherein the baby’s heart, brain, kidneys, and lungs are measured and assessed (parents can find out the sex of the baby at this time, if desired) (1).

Many women have a larger appetite during the second trimester, and thus gain more weight during the second trimester. It is important to check in with your doctor about your weight gain to make sure it’s not exceeding the recommended amount. You should also do light exercise and maintain your healthy diet as your baby grows. Genetic screening tests are commonly administered during the second trimester; ask your doctor about anything in your medical or genetic history that could put your baby at risk. Doctors will also test for gestational diabetes during the second trimester, between 26-28 weeks.

Second trimester maternal physical changes

The second trimester is often marked by some respite from early pregnancy symptoms, higher energy levels, and better mood (3). Some new physical changes may still occur, including:

  • Heartburn
  • Leg cramps
  • Backaches
  • Sensitive gums
  • Congestion
  • Mild swelling of ankles and feet
  • Varicose veins
  • Dizziness
  • Increase in appetite and pregnancy weight gain

The third trimester

28 weeks – birth

What’s happening?

During the third trimester, the baby is growing more quickly than in previous trimesters (4). The fetus will start out at roughly 2.5 pounds and 16 inches long and grow to between 6-9 pounds and 19-22 inches long by week 40.

During the third trimester, the following occur (4):

  • Your baby will be able to regulate their own body temperature, dream, and blink.
  • The skin will transform from transparent to opaque by 32 weeks. Your baby will also shed their vernix, the layer over the skin that protects the baby from the amniotic fluid.
  • The baby will shed the hairy layer that regulates warmth, called lanugo (4).
  • The cartilage will turn into bones during the 7th and 8th months.
  • Meconium starts to build up in the intestines in the last few weeks of pregnancy.
  • During the third trimester, your baby will acquire the ability to perceive light and darkness.
  • Around week 34, your baby will likely turn to the head-down, bottom-up position in preparation for birth. In some cases, the baby will remain in breech position

Important notes

During the third trimester, you will see your doctor more regularly (1). Your doctor will check your blood pressure, test your urine, listen to the fetal heart rate, check your hands and legs for swelling, and measure fundal height (approximate length of the uterus). Your doctor will also check your cervix to monitor the body’s readiness for labor and delivery. You will likely be screened for Group B Streptococcus (GBS), a bacteria which can severely harm newborns. If you are GBS-positive, you may need to take antibiotics to keep the baby from getting it. 

Some things you might want to do during the third trimester include (4):

  • Tour your hospital: It’s a great idea to visit your hospital and learn about where you’ll be laboring and giving birth.
  • Interview pediatricians: You will need to choose a pediatrician for your baby before they are born. It’s a good idea to ask your potential pediatrician how they feel about those issues that are more important to you. 
  • Count kicks: Your doctor will likely instruct you to monitor fetal movement by doing kick counts after 28 weeks. 
  • Buy baby needs: It’s a good idea to purchase or borrow baby essentials before heading to the hospital. There are many ways  to acquire the necessities, including a crib, feeding tools (breast pumps should be provided free through medical insurance plans), a car seat, a changing table, and clothing.
  • Restrict travel: You should remain in close proximity to your doctor or midwife in case you go into labor early, and it is advised that you don’t fly or board a cruise ship.
  • Take classes: You may want to use the third trimester to take courses on childbirth, parenting, CPR, and other relevant subjects in preparation for delivery and beyond.
  • Learn what to expect: It’s a good idea to learn what happens during birth, what after birth looks like, and what to expect for the first year. 
  • Learn about cord blood banking: Consider cord blood banking and mention it to your practitioner. 
  • Pack your hospital bag: You will need to prepare your hospital bag for labor and delivery. Important items to pack include toiletries, a change of comfortable clothes, and a cell phone charger, among others.

Third trimester maternal physical changes

Physical changes that may occur during the third trimester include (4):

  • Fatigue
  • Abdominal aches from carrying the weight of the baby
  • Varicose veins
  • Braxton Hicks (false or practice) contractions
  • Heartburn
  • Backache
  • Stretch marks
  • Lactation
  • Clumsiness
  • Lack of bladder control


37-42 weeks (typically)

A normal pregnancy usually results in birth at between 37-42 weeks. The due date is estimated from the first day of your last period, adding 40 weeks to that date.

What to look for

Signs of labor include (4):

  • Bloody show: A stringy mucus discharge that is tinged pink or brown with blood. It may be accompanied by the passing of the mucus plug, which is the seal of the uterus. 
  • Labor contractions: Unlike Braxton Hicks contractions, real labor contractions grow more intense and are not eased by movements or changes in position. 
  • Water breaking: This doesn’t happen for all women, but some women will feel their “water break”: a surge of wetness in their underwear.

Call your doctor if you experience any of these symptoms, and they will direct you as to when to head to the hospital (2). If your water breaks, you will need to go to the hospital quickly to prevent infection. 

About ABC Law Centers

ABC Law Centers was established to focus exclusively on birth injury cases. A “birth injury” is any type of harm to a baby that occurs just before, during, or after birth. This includes issues such as oxygen deprivation, infection, and trauma. While some children with birth injuries make a complete recovery, others develop disabilities such as cerebral palsy and epilepsy.

If a birth injury/subsequent disability could have been prevented with proper care, then it constitutes medical malpractice. Settlements from birth injury cases can cover the costs of lifelong treatment, care, and other crucial resources. 

If you believe you may have a birth injury case for your child, please contact us today to learn more. We are happy to talk to you free of any obligation or charge. In fact, clients pay nothing throughout the entire legal process unless we win. 

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  1. What Happens During the Trimesters of Pregnancy? (n.d.). Retrieved November 18, 2018, from
  2. Editors, W. T. (2018, August 31). Your Guide to the First Trimester of Pregnancy. Retrieved November 19, 2018, from
  3. Editors, W. T. (2018, September 04). Your Guide to the Second Trimester of Pregnancy. Retrieved November 19, 2018, from
  4. Editors, W. T. (2018, September 05). Your Guide to the Third Trimester of Pregnancy. Retrieved November 19, 2018, from

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