At just four weeks pregnant, your embryo — no bigger than a period on a page, measuring 1/25 of an inch — is already forming the foundational layers that will become its brain, heart, lungs, kidneys, and digestive system. The zygote has completed its journey from the fallopian tube, implanted in the uterine wall, and divided into two distinct structures: the embryo itself and the placenta that will sustain it until birth. Mothers at this stage may notice PMS-like symptoms including mood swings, bloating, breast tenderness, and a heart rate increase of up to 15 extra beats per minute — all driven by rising levels of progesterone and oestrogen. Nutritionally, eating one to three oranges daily is recommended at this stage, as they supply vitamin C, folic acid, vitamin B6, potassium, and iron — nutrients that support the baby's brain development and cardiovascular health while reducing the mother's risk of infection.
- By the end of pregnancy week 4, the baby measures 1/25 inches long — approximately the size of a period (dot).
- During week 4, the zygote completes its journey from the fallopian tube to the uterus and divides into 2 parts: the embryo and the placenta.
- The inner cell layer, called the endoderm, develops into the baby's liver, lungs, and digestive system during week 4.
- The second cell layer, the mesoderm, develops into the baby's kidneys, sex organs, bones, muscles, and heart.
- At week 4, a pregnant woman's heart rate may increase by an additional 15 beats per minute.
- Pregnant women are advised not to eat more than 2–3 regular-size oranges per day, as excess consumption can cause stomach acidity, cramps, and heartburn.
- Eating at least 1 orange per day during early pregnancy may help protect against infections and support haemoglobin production through its Vitamin B6 content.
Pregnancy Diary Week 4
Discover your pregnancy journey
Pregnancy Diary Week 4
Although it is very early days, you are aware of changes, but you may not even have done a pregnancy test as yet. Here’s some of what can be happening for you during pregnancy week 4 in terms of baby’s development and how you’re feeling. Plus check out the nutritional benefits of oranges for you and your baby.
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How your baby is growing
What you can expect at this time
A beneficial food for your pregnancy nutrition
Pregnancy Diary Week 4: How Is Your Baby Growing?
By this time, the journey of the zygote from the fallopian tube to the uterus should have been completed. On the fourth week, the uterus begins to thicken and it continues until the 4th month of your pregnancy. The zygote settles into the uterine lining and divides into two. The first half becomes the embryo and the second half forms a placenta which serves as the baby’s lifeline until the delivery.
During this period, the embryo begins to develop. The inner layer develops into the baby’s liver, lungs and the digestive system. This layer is known as the endoderm. Also known as the mesoderm, the second layer develops into the baby’s kidneys, sex organ, bones, muscles and heart. On the other hand, the outer layer, which is known as ectoderm, forms into the baby’s nervous system as well as the eyes, hair, skin. The growth and development of the organs at this stage is impressively rapid.
What you can expect
At this stage, the signs and symptoms of your pregnancy might have become more evident. Just like the major changes taking place inside the body, you should also anticipate some changes outside the body. You may begin experiencing some PMS like symptoms. You probably have complained about dizziness, light-headedness, abdominal cramps, pains, morning sickness and feelings of fainting.
Early pregnancy symptoms such as mood swings and cramping may be obvious to you. Bloating can also be expected at this point in time. Blame it on the progesterone. This hormone slows down your digestion in order to allow nutrients to enter into your bloodstream. You’re constantly changing mood can also be blamed on your hormones. You might have a slight bleeding due to the implantation of zygote into your uterus.
You might even notice a little pressure on your stomach but this shouldn’t cause you to worry. It is pretty normal during this stage. Your breasts may become more tender and appear bigger, and as time passes by, you will notice significant change in their size. Also, the breasts can become sore, tingly and fuller. This is due to the increase of hormones such as progesterone and oestrogen in your system.
By this time, your heart should be beating more rapidly. In fact, you might have an additional 15 beats per minute. And you may feel tired most of the time, which may lead to you falling asleep more frequently. By the end of the 4th week of your pregnancy, your baby should be 1/25 inches long which is equivalent to a period (dot).
Oranges For Pregnancy Nutrition
Oranges are probably one of the best fruits to eat during this early stage of pregnancy. Oranges are citrus fruits which provide additional protection to pregnant women. According to research, taking at least one orange in a day makes the body less prone to infections. It offers plenty of vitamin C which provides additional protection and resistance against diseases such as cancer and osteoporosis.
Furthermore, oranges are packed with massive amount of Vitamin B6 which is beneficial during the process of haemoglobin production. In effect, pregnant women are less likely to suffer from haemoglobin deficiency during this very crucial stage.
Oranges are also beneficial to the baby. This citrus fruit contains ample amount of folic acid and Vitamin B which are beneficial in the baby’s brain development. The fruit also contains high level of potassium and iron which ply vital roles in protecting the cardiovascular system of the body, especially the heart. Though this citrus fruit is beneficial to the body, pregnant women should not eat more than 2-3 regular size oranges, as it can cause stomach acidity, stomach cramps and heartburn.
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Pregnancy Diary Week 4
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DISCLAIMER
All articles on the blog and website are intended as information only. Please do not consider any of the information provided here as a substitute for medical advice. At all times seek medical advice directly with your own doctor and medical team.
ANNOUNCEMENT
This website was formerly Merrion Fetal Health. The clinic has undergone a rebrand and is now known as Merrion Ultrasound.
What is happening to a baby's development at week 4 of pregnancy?
At week 4, the zygote completes its journey from the fallopian tube to the uterus and divides into two parts — one becomes the embryo and the other forms the placenta. Three distinct layers begin developing: the endoderm (liver, lungs, digestive system), mesoderm (kidneys, sex organs, bones, muscles, heart), and ectoderm (nervous system, eyes, hair, skin). By the end of week 4, the baby is approximately 1/25 of an inch long, roughly the size of a period (dot).
What are the common symptoms of pregnancy at week 4?
Common week 4 pregnancy symptoms include dizziness, light-headedness, abdominal cramps, morning sickness, mood swings, bloating, and breast tenderness. Some women may also experience slight implantation bleeding as the zygote embeds into the uterine lining. Fatigue is also common, and heart rate may increase by an additional 15 beats per minute.
Why do pregnant women experience bloating at week 4?
Bloating at week 4 is caused by the hormone progesterone, which slows down digestion to allow more nutrients to enter the bloodstream. This hormonal change is a normal part of early pregnancy. Mood swings at this stage are also attributed to hormonal fluctuations.
What causes breast tenderness and swelling in early pregnancy?
Breast tenderness, soreness, tingling, and fullness in early pregnancy are caused by increased levels of the hormones progesterone and oestrogen. These changes begin as early as week 4 and become more pronounced as pregnancy progresses. The breasts may also appear noticeably larger over time.
Are oranges good to eat during early pregnancy?
Oranges are considered one of the best fruits to eat during early pregnancy because they provide vitamin C, vitamin B6, folic acid, potassium, and iron. Vitamin B6 supports haemoglobin production, while folic acid and vitamin B aid the baby's brain development. Potassium and iron also help protect the cardiovascular system.
How many oranges should a pregnant woman eat per day?
Pregnant women should limit their orange intake to no more than 2–3 regular-size oranges per day. Eating more than this can cause stomach acidity, stomach cramps, and heartburn. Despite these risks, consuming at least one orange daily can help reduce the body's susceptibility to infections.
What is the difference between the endoderm, mesoderm, and ectoderm in a week 4 embryo?
In a week 4 embryo, the endoderm is the inner layer that develops into the liver, lungs, and digestive system, while the mesoderm (middle layer) forms the kidneys, sex organs, bones, muscles, and heart. The ectoderm is the outer layer and develops into the nervous system, eyes, hair, and skin.
What is implantation bleeding and when does it occur?
Implantation bleeding is a slight bleeding that can occur when the zygote embeds itself into the uterine lining, typically around week 4 of pregnancy. It is considered a normal early pregnancy symptom and should not be a cause for concern. Some women may also feel a mild pressure on their stomach at this stage.