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The Amazing Journey of Pregnancy: the First Trimester

The possibility of pregnancy brings a wide variety of emotions, be it planned or unplanned. Despite the complicated feelings surrounding it, there’s no doubt that the process of pregnancy is a miracle. In this post, we’re exploring the amazing journey of pregnancy from conception through the 13th week (also known as the 1st trimester).

Before we do, please know that if you are faced with the possibility of pregnancy and aren’t sure where to turn next, Life’s Choices is here to support you and empower you with the resources necessary to embark on your personal journey. You’re not alone. The first step in making your decisions surrounding your pregnancy is to make sure you are fully educated about the facts surrounding the pregnancy process. Here’s what to know about the first trimester:


A miraculous journey has begun! An egg (oocyte) is released from the ovary into the fallopian tube inside the female body. Small finger like hairs called cilis in the fallopian tube, propel the egg along in anticipation for fertilization. Fertilization takes place in the fallopian tube when an egg is penetrated by a single sperm; each sperm and egg contain 23 chromosomes that when combined transform to make a unique human being with its own set of 46 chromosomes (DNA).

Once this single sperm has united with the egg, a hard protective shell-like membrane, called a zona pellucida, forms around the outside of the newly formed fertilized egg (embryo). This process occurs to protect the embryo from being fertilized by multiple sperm, as one deposit (ejaculation) of sperm from a man to a woman contains 40-150 million sperm which can live inside the woman’s reproductive organs for up to five days.


first trimester

Attribution: Ttrue12, CC BY-SA 3.0, via Wikimedia Commons

The journey for this newly created human being has now begun in the form of an embryo. The embryo is a time in a human’s life that he/she will experience the most rapid development ever, and it all takes place in just eight short weeks. The embryo itself consists of three different stages:

  1. ZYGOTE: The first stage is referred to as a zygote. This stage lasts approximately four to five days. During this stage, the cells within the zygote are multiplying to created millions of other cells that are the building blocks (DNA) to each unique person and are responsible for the development of every organ system, hair color, sex, etc., that will follow him or her throughout that person’s entire life.

  2. BLASTOCYST: After those very busy four to five days, the hard protective shell, or zona pellucida begins to break down to allow for expanded growth of the embryo now referred to as a blastocyst. Let’s pause for a moment and consider how incredible that the embryo is protected and shielded for five days post fertilization; the same number of days that sperm can live within the female reproductive organs. Another unique thing that happens during the blastocyst stage, is the embryo is developing a yolk sac and yolk stem that will support all the baby’s nutritional and circulatory needs until the umbilical cord and placenta can be established. As the placenta and umbilical cord are formed, the yoke sac and yolk stem are simply absorbed into the baby’s gastrointestinal tract. It’s amazing how the yolk sac and stem mimic almost completely the look and function of the placenta and umbilical cord. The yolk sac is also responsible for producing the hormone HCG (Human Chorionic Gonadotrophin). This is the hormone used to help identify a pregnancy and can start being detected in the blood and urine of the pregnant woman as little as one week post fertilization. It is this hormone, along with rising levels of estrogen and progesterone, that helps to support the beginning stages of pregnancy and are responsible for a lot of those early signs/symptoms of pregnancy: nausea (AKA morning sickness), breast swelling/tenderness, darkening of skin pigmentation on the face(melasma), around the breast areola (nipple), fatigue, bloating, constipation, just to name a few. For most women, these annoying symptoms will tend to subside once they move into their second trimester. However, please ALWAYS consult your obstetrician prior to any medication or herbal use.

  3. GASTRULA: As the embryo continues to develop during the blastocyst stage, it is gently guided through the fallopian tubes by the cilia until about day nine post fertilization. It is at this point in the journey that the embryo enters the uterus and finds its way into a blood-filled protective lining of the uterus known as the endometrial layer. This process is also known as implantation and the embryo has now entered the stage known as “gastrula. It is also during this stage that the majestic sound of the baby’s heart starts beating; this will happen at approximately three to four weeks post fertilization or what would also be known as five to six weeks gestation of pregnancy, as pregnancy gestation is based on the first day of your last menstrual cycle and not conception date. (The pregnancy/baby’s development is referred to as gestational weeks.) This means that one to two weeks after a woman misses her menstrual cycle — many times even before a woman knows she’s pregnant – her baby’s heart has formed and begun to beat.


By 10 weeks gestation, all of the baby’s major organ systems and appendages have developed: the brain, nervous system, circulatory system, digestive system, legs, arms, fingers, and toes. The sex organs, eyes, and ears are also starting to develop. The yolk sac and stem have now been absorbed into the digestive system, and the umbilical cord and placenta are now established. The placenta and umbilical cord will now be the means in which nutrients and oxygen rich blood will be delivered to the baby from the mother, and waste byproducts will be released from the baby back to the mother.

Fun fact: If you take negative images of lungs, a tree route system, and the vasculature in a baby’s placenta, visually they all mimic each other. They are all incredibly interdependent upon each other delivering life-sustaining oxygen for the humans and carbon dioxide for the trees. What a masterful design!

Now at 10 weeks gestation, the baby is no longer referred to as an embryo and is now referred to as a fetus measuring approximately one inch long. The fetus will continue to grow rapidly over the next few weeks measuring between three to four inches long by 13 weeks, ending the journey of the fast and furious 1st trimester yet entering the exciting adventure of what will be the second trimester.


To learn about the wonders that occur during the second trimester, keep following along! We’re excited to share later this month this second part of the amazing journey of pregnancy. For more educational and practical information about the pregnancy journey, we encourage you to sign up for Life’s Choices’ free prenatal classes. Learn more about our free class options here:

“…For you created my inmost being; you knit me together in my mother’s womb. I praise you because I am fearfully and wonderfully made; your works are wonderful, I know that full well. My frame was not hidden from you when I was made in the secret place, when I was woven together in the depth of the earth. Your eyes saw my unformed body; all the days were ordained for me were written in your book before one of them came to be…” Psalm 139:13-16


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