SSM Health: First Trimester Development

From the SSM Health St. Clare Hospital - Fenton:

June 30, 2021

By SSM Health

Oh, baby…the first trimester of pregnancy can be full of so many emotional and physical changes. And no matter how much you try to prepare yourself, that surge of pregnancy hormones can be downright intense.

Almost as soon as you find out you’re pregnant, you’re flooded with feelings of excitement, anticipation, and uncertainty as well as exhaustion, anxiety, and even fear. And there’s the physical changes. Your breasts may quickly swell and become incredibly sore. You may even develop adult acne (so much for that pregnancy glow) and suffer from unfortunate bouts of morning sickness – a misleading term, for the record.

In short, the myriad of changes can be overwhelming. So, to help you better navigate this stage of pregnancy, we’re breaking down what to expect during the first trimester – which begins on the first day of your last menstrual period and runs through week 13 – including your symptoms as well as how your baby’s developing.

I’m Pregnant…What’s Next?

If you took an at-home pregnancy test and it was positive, you’ll want to schedule your first prenatal appointment with your OB/GYN, who’ll confirm the pregnancy, prescribe prenatal vitamins, administer routine blood testing, and listen for your baby’s heartbeat. You may also have your first ultrasound at this time, where you can see your baby in embryonic form.

The Do’s

At that first appointment, your OB/GYN will also recommend the following guidelines for a healthy, safe pregnancy:

• Take a daily prenatal vitamin
• Eat a well-balanced diet
• Eat no more than two servings of seafood per week (due to mercury levels in some fish)
• Drink plenty of water (64 ounces per day)
• Get enough sleep (8 hours per night).
• Exercise daily (walking, swimming, yoga, etc., with your doctor’s permission)

…And Don’ts

Additionally, your OB/GYN may advise you to avoid or limit the following during your pregnancy:

• Limit your caffeine intake to 200 milligrams per day (e.g., 12 ounces of coffee)
• Avoid certain foods including raw fish (sushi) and raw or partially cooked eggs and meats
• No alcohol, tobacco, or substance abuse
• Avoid being around hazardous materials such as certain chemical cleaners without proper ventilation
• Do not participate in contact sports and riskier sports like downhill skiing, horseback riding and diving
• Avoid lying flat on your back, especially while sleeping, because the pressure of your growing uterus can affect the blood flow to your heart
• Reduce your stress, which may increase the risk of preterm labor, low birth weight and possibly miscarriage

First Trimester Symptoms

In addition to these lifestyle changes, early pregnancy brings other new changes – physical and emotional – which are completely normal and can even change with each pregnancy. Most will begin to subside as you enter the second trimester. Some of the normal changes you may experience include:

• Mood swings, which are fueled by surging pregnancy hormones
• Nausea and/or vomiting (also known as morning sickness, even though it may occur at any time of the day)
• Constipation
• Fatigue or exhaustion from the hormones
• Headaches or dizziness from the hormonal changes
• Breast tenderness or an increase in breast size
• Light bleeding or spotting, which often occurs upon implantation around the fourth week of pregnancy
• Frequent urination
• Unusual cravings
• Food/smell aversions
• Acne due to an increase in oil production from the hormones
• Skin discoloration or darkening in certain areas, which often fade after birth

Your Baby’s Development in the First Trimester

While you’re experiencing numerous changes, your baby is rapidly changing during the first trimester as well. In those first three weeks alone, your baby’s brain, spinal cord, heart, and tiny limbs begin to develop.

Embryonic Period (Weeks 4 to 8)

The fourth week marks the beginning of the embryonic period, when your baby goes from being a compact ball of cells to an embryo about the size of a poppy seed. This is also when the embryo implants in the wall of the uterus, which may cause mild bleeding or spotting.

Over the course of the next four weeks, your baby’s developments will include the following:

• Baby’s arm and leg buds are now visible
• The brain develops into five areas
• Eye and ear structures form
• Tissue that will become the vertebra and other bones begins to form
• Continued development of the heart, which now beats with a regular rhythm
• Blood begins moving through the main vessels

Fetal Period (Weeks 9 to 13)

The ninth week marks the beginning of the fetal period. You won’t be able to notice, but your baby – measuring one inch long – is constantly moving around in your uterus. Between the tenth and eleventh weeks, your baby’s heartbeat is beating loudly enough that it can be detected on a Doppler ultrasound.

By the end of the first trimester, your baby measures approximately three inches long and weighs one ounce (about the size of a lemon). Your baby has hands and fingerprints, is beginning to grow fingernails, and can swallow and discharge fluids. Other major developments include:

• Face is well formed
• Limbs become long and thin
• Genitals are noticeable
• Vocal cords are forming
• The head makes up nearly half of your baby’s size
• Your baby can make a fist with his or her fingers
• Tooth buds appear for the baby teeth
• Eyelids will close and won’t reopen until about the 28th week

The first trimester certainly promises lots of changes for both you and your baby. They’re a good sign that your body is doing what it needs to nurture your baby and sustain a healthy pregnancy. However, if you experience any unusual symptoms, don’t hesitate to call your OB/GYN. Your goal – and your OB/GYN’s goal – is to have an uneventful, uncomplicated pregnancy that results in a healthy baby and a healthy you.

If you live in the St. Louis area, SLUCare OB/GYN and Women’s Health at SSM Health St. Mary’s Hospital offers comprehensive care for women at every stage of life — from pediatric and adolescent care to pre-pregnancy planning and counseling through pregnancy and beyond.

For more information about prenatal care and what to expect when you’re expecting, visit our site.

This press release was produced by the SSM Health St. Clare Hospital - Fenton. The views expressed are the author's own.