Fetus at 6 Weeks: Development, Size, and What to Expect

At 6 weeks pregnant, you’re experiencing one of the most critical stages of early pregnancy. While you may have just discovered you’re pregnant or confirmed it recently, remarkable changes are already happening inside your body. Understanding what your developing baby looks like and what’s occurring during this crucial time can help you navigate the early weeks of pregnancy with confidence.

At this stage, your baby is technically called an embryo rather than a fetus, but the term “fetus at 6 weeks” is commonly used when discussing early pregnancy development. This week marks significant milestones in your baby’s growth, including the development of vital organs and the beginning of a recognizable human form.

How Big Is the Fetus at 6 Weeks?

At 6 weeks of pregnancy, your baby is incredibly tiny but growing rapidly. The embryo measures approximately 0.25 inches (4 to 5 millimeters) in length from crown to rump. To put this in perspective, your baby is about the size of a sweet pea, lentil, or small pomegranate seed.

Despite being so small, your developing baby is undergoing dramatic transformations. The embryo has grown significantly from the previous week, nearly doubling in size. This rapid growth will continue throughout the first trimester as cells multiply and differentiate into specialized tissues and organs.

Major Developmental Milestones at 6 Weeks

Neural Tube Formation

One of the most critical developments happening at 6 weeks is the closing of the neural tube. This structure runs along your baby’s back and will eventually develop into the brain and spinal cord. The neural tube typically closes during the sixth week of pregnancy, which is why adequate folic acid intake before and during early pregnancy is so important. Proper neural tube development is essential for preventing neural tube defects such as spina bifida.

Heart Development and Function

Perhaps one of the most exciting milestones at 6 weeks is that your baby’s heart is beginning to beat. The primitive heart has formed and is starting to pump blood through tiny vessels. At this stage, the heart beats at approximately 100 to 160 times per minute, which is roughly twice as fast as your own heart rate. In many cases, this heartbeat can be detected on an ultrasound, though it depends on the quality of the equipment and the position of the embryo.

Facial Features Begin to Form

The beginnings of facial features start to appear during week 6. Dark spots mark where your baby’s eyes and nostrils will develop. Small depressions on the sides of the head indicate where the ears will form. The jaw and cheeks are also starting to take shape, though the face won’t look fully formed for several more weeks.

Limb Buds Emerge

Small buds that will eventually become your baby’s arms and legs begin to appear at 6 weeks. The arm buds are typically visible slightly before the leg buds develop. These paddle-shaped protrusions will gradually lengthen and differentiate into distinct segments that will become shoulders, arms, elbows, forearms, and hands.

Internal Organ Development

Major organs are beginning to form during the sixth week of pregnancy. The liver, kidneys, lungs, and intestines are all starting to develop. The digestive and respiratory systems are in their earliest stages of formation. Additionally, the pituitary gland at the base of the brain begins to develop, which will eventually control hormone production throughout your baby’s life.

Body Shape Changes

Your baby’s body begins to take on a characteristic C-shaped curve at 6 weeks. The embryo has a prominent head region and a tail-like structure that will eventually become the lower spine and legs. While your baby doesn’t look quite human yet, the basic body plan is being established.

What You Might Experience at 6 Weeks Pregnant

Pregnancy Symptoms

At 6 weeks, pregnancy hormones are surging through your body, which often leads to noticeable symptoms. Common experiences include:

• Morning sickness: Despite its name, nausea and vomiting can occur at any time of day. Many women begin experiencing morning sickness around week 6, though some may have started earlier or may not experience it at all.
• Breast tenderness: Your breasts may feel swollen, sore, or sensitive to touch as they begin preparing for milk production.
• Fatigue: Extreme tiredness is common during early pregnancy as your body works hard to support your developing baby.
• Frequent urination: You may notice you need to urinate more often as pregnancy hormones increase blood flow to your kidneys.
• Food aversions or cravings: Your sense of smell may become more sensitive, and you might develop strong preferences or aversions to certain foods.
• Mood swings: Hormonal changes can affect your emotions, leading to mood fluctuations.
• Mild cramping: Some women experience light cramping as the uterus expands, though severe pain should be reported to your healthcare provider.

Physical Changes

While you probably won’t show yet at 6 weeks, your body is changing internally. Your uterus is expanding, though it’s still within your pelvis. You may notice bloating that makes your clothes feel tighter around the waist. Your blood volume is beginning to increase to support the growing placenta and embryo.

The Placenta and Amniotic Sac at 6 Weeks

The placenta is rapidly developing at 6 weeks, though it won’t be fully functional for a few more weeks. This remarkable organ will serve as the life-support system for your baby throughout pregnancy, providing oxygen and nutrients while removing waste products.

The amniotic sac, which contains amniotic fluid, surrounds and protects your developing baby. This fluid-filled environment provides cushioning and allows your baby to move freely as they grow. The amniotic fluid also helps maintain a constant temperature and protects against infection.

What Happens During a 6-Week Ultrasound?

If you have an ultrasound at 6 weeks, it will likely be a transvaginal ultrasound, which provides a clearer view of the embryo at this early stage. During the scan, your healthcare provider will look for:

• Gestational sac: The fluid-filled structure that surrounds the embryo
• Yolk sac: A circular structure that provides nutrients to the embryo until the placenta takes over
• Fetal pole: The early embryo itself
• Heartbeat: The flickering motion of the developing heart, though it may not always be visible at exactly 6 weeks

It’s important to note that dating can vary, and if a heartbeat isn’t detected at 6 weeks, your healthcare provider may schedule a follow-up ultrasound in a week or two. Every pregnancy develops at a slightly different pace, and being off by even a few days can make a difference in what’s visible on an ultrasound.

Important Health Considerations at 6 Weeks

Prenatal Vitamins

If you haven’t already started taking prenatal vitamins, now is the time to begin. Folic acid is particularly crucial during these early weeks when the neural tube is closing. Most healthcare providers recommend at least 400 to 800 micrograms of folic acid daily. Prenatal vitamins also typically contain iron, calcium, and other essential nutrients needed for your baby’s development.

Avoid Harmful Substances

The first trimester is a critical period of organ formation, making it essential to avoid substances that could harm your developing baby:

• Alcohol: No amount of alcohol is considered safe during pregnancy
• Tobacco: Smoking increases risks of complications and should be stopped immediately
• Recreational drugs: All illegal drugs should be avoided
• Certain medications: Always consult your healthcare provider before taking any medication, including over-the-counter drugs and supplements
• High-mercury fish: Limit consumption of fish high in mercury such as shark, swordfish, and king mackerel

Diet and Nutrition

Eating a balanced diet supports your baby’s growth and helps manage pregnancy symptoms. Focus on:

• Lean proteins to support cell growth
• Whole grains for energy and fiber
• Fruits and vegetables for vitamins and minerals
• Dairy products for calcium and vitamin D
• Plenty of water to stay hydrated

If morning sickness makes eating difficult, try small, frequent meals and focus on foods that you can tolerate. Many women find that bland, dry foods like crackers are easier to keep down.

When to Contact Your Healthcare Provider

While some discomfort is normal during early pregnancy, certain symptoms warrant immediate medical attention:

• Severe abdominal pain or cramping
• Heavy bleeding or passing tissue
• Severe nausea and vomiting that prevents you from keeping any food or fluids down
• Fever above 100.4°F (38°C)
• Painful urination or other signs of infection
• Sudden severe headache or vision changes

Miscarriage Risk at 6 Weeks

It’s natural to worry about miscarriage during early pregnancy. The risk is highest during the first trimester, with most miscarriages occurring before 12 weeks. However, once a heartbeat is detected on ultrasound, the risk of miscarriage decreases significantly.

Most miscarriages that occur in early pregnancy are due to chromosomal abnormalities and are not caused by anything the mother did or didn’t do. If you experience signs of miscarriage such as heavy bleeding or severe cramping, contact your healthcare provider immediately.

Emotional Well-Being During Early Pregnancy

The early weeks of pregnancy can be emotionally challenging. You may feel excited, anxious, overwhelmed, or all of these emotions at once. Hormonal changes can intensify feelings, and it’s completely normal to experience a range of emotions.

Consider these strategies for supporting your emotional health:

• Connect with other expectant parents through support groups or online communities
• Talk openly with your partner, friends, or family about your feelings
• Practice stress-reduction techniques such as gentle prenatal yoga or meditation
• Get adequate rest and prioritize self-care
• Seek professional support if you’re experiencing persistent anxiety or depression

Looking Ahead: What Comes Next

After 6 weeks, your baby will continue to develop rapidly. In the coming weeks, you can expect:

• Continued organ development and refinement
• Formation of fingers and toes
• Further development of facial features
• Growth of bones and muscles
• Development of the digestive and urinary systems

By the end of the first trimester at 12 weeks, all major organs will have formed, though they will continue to mature throughout pregnancy. Your baby will look more recognizably human, with a defined head, body, and limbs.

Preparing for Your Prenatal Appointments

If you haven’t already scheduled your first prenatal appointment, now is an excellent time to do so. Your healthcare provider will likely schedule your first visit sometime between 6 and 10 weeks of pregnancy. During this appointment, you can expect:

• Confirmation of your pregnancy through blood or urine tests
• Calculation of your due date based on your last menstrual period
• A complete medical history and physical examination
• Discussion of your symptoms and any concerns
• Blood tests to check your blood type, Rh factor, and screen for various conditions
• Possibly an ultrasound to confirm the pregnancy and check for a heartbeat

Come prepared with questions and a list of any medications or supplements you’re currently taking. It’s also helpful to know your family medical history and that of your baby’s father.

Common Questions About the Fetus at 6 Weeks

Can you see the fetus at 6 weeks?

Yes, the embryo can typically be seen on a transvaginal ultrasound at 6 weeks, though it will appear as a small flickering dot. The gestational sac and yolk sac are usually more clearly visible. Whether a heartbeat can be detected depends on the exact timing and the equipment used.

Is it an embryo or fetus at 6 weeks?

At 6 weeks pregnant, your baby is technically called an embryo. The term “fetus” isn’t used until week 11 of pregnancy (9 weeks after conception), when the embryonic period ends and the fetal period begins. However, many people use the terms interchangeably when discussing early pregnancy.

What does the fetus look like at 6 weeks?

At 6 weeks, the embryo has a curved, somewhat tadpole-like shape with a large head region relative to the body. Small buds where arms will develop are visible. The embryo has a tail-like structure that will later become the lower spine. Dark spots indicate where the eyes are forming, and the beginnings of ears and nose are present.

Can you hear a heartbeat at 6 weeks?

While the heart begins beating around 6 weeks, whether it can be detected depends on several factors including the exact gestational age, the position of the embryo, and the type of ultrasound equipment used. A transvaginal ultrasound provides the best chance of detecting a heartbeat this early. If a heartbeat isn’t detected at 6 weeks, your healthcare provider will likely schedule a follow-up scan.

Conclusion

At 6 weeks pregnant, your tiny embryo is undergoing remarkable transformations. From the closing of the neural tube to the beginning heartbeat, these early weeks establish the foundation for your baby’s entire development. While you may be experiencing uncomfortable symptoms, remember that these are signs your body is working hard to nurture your growing baby.

Focus on taking care of yourself by eating nutritious foods, taking prenatal vitamins, avoiding harmful substances, and getting plenty of rest. Stay in close contact with your healthcare provider and don’t hesitate to reach out with questions or concerns. Every pregnancy is unique, and your medical team is there to support you through this incredible journey.

The coming weeks will bring even more exciting developments as your baby continues to grow and your pregnancy progresses. Embrace this special time and trust in your body’s amazing ability to create and nurture new life.

Sources:

• American College of Obstetricians and Gynecologists – How Your Fetus Grows During Pregnancy
• Mayo Clinic – Prenatal Care
• March of Dimes – Your Baby’s Growth and Development
• Centers for Disease Control and Prevention – Pregnancy
• MedlinePlus – Fetal Development