Pregnancy Weeks 1 to 5: A Guide for Moms-to-Be

Even before a pregnancy is confirmed, significant changes occur in your body. After fertilisation, the egg travels to the uterus and implants itself, triggering hormonal shifts that support early development. Some women start feeling more tired than usual, experience nausea, or notice breast tenderness, while others feel no different. By week five, as hormone levels continue to rise, these changes may become more noticeable. Understanding this early phase can help with recognising symptoms and making informed choices. This guide walks you through weeks one to five, covering key developments, common signs, and essential do’s and don’ts.

Weeks 1 & 2

Pregnancy is typically counted from the first day of the last menstrual period (LMP), even though conception has not yet taken place. During weeks 1 and 2, the body prepares for ovulation, releasing hormones that support the potential for pregnancy

Key Developments This Week

Menstruation and Hormonal Shifts (Week 1)

The cycle begins with menstruation, during which the uterine lining sheds from the previous cycle. At this stage, hormone levels, particularly oestrogen and progesterone, are low, but they gradually start to rise. The brain signals the ovaries to begin developing follicles, each containing an immature egg, in preparation for ovulation.

Ovulation and Egg Maturation (Week 2)

One follicle becomes dominant and matures, eventually releasing an egg around day 14 in a 28-day cycle. The egg then enters the fallopian tube, where it remains viable for about 12–24 hours, awaiting fertilisation. Cervical mucus becomes clearer and more elastic to facilitate sperm movement, while the uterine lining thickens in preparation for a possible pregnancy.

Symptoms and Signs

At this stage, there are usually no noticeable pregnancy symptoms because implantation has not yet occurred. However, ovulation signs may be noticeable, that include:

• Increased cervical mucus – Ovulation causes a clear, stretchy discharge, which helps sperm travel.
  
  
• Mild pelvic discomfort – Some experience ovulation pain on one side of the lower abdomen.
  
  
• Higher basal body temperature – A slight rise in temperature after ovulation can indicate the fertile window.

Week 3

Week 3 marks the actual beginning of pregnancy, as fertilisation takes place. If an egg meets a sperm, a new life begins at the cellular level. This is a crucial stage where genetic material is determined, and early development starts before implantation occurs.

Read More: Pregnancy Due Date Calculator

Key Developments This Week

Fertilisation: The Union of Egg and Sperm

After ovulation, the egg has a short window of about 12 to 24 hours to be fertilised. If sperm is present in the fallopian tube at the right time, one will successfully penetrate the egg, combining genetic material from both parents. This single-cell structure, now called a zygote, carries all the DNA needed to determine the baby's sex, eye colour, and other inherited traits.

Cell Division and Blastocyst Formation

Soon after fertilisation, the zygote begins dividing rapidly while making its way through the fallopian tube. Within a few days, it transforms into a cluster of cells known as a blastocyst. This tiny structure has an outer layer that will eventually develop into the placenta, while the inner cells will form the embryo. The journey to the uterus continues over the next several days as the blastocyst prepares for implantation.

Preparation for Implantation

By the end of the week, the blastocyst reaches the uterus but does not attach immediately. Instead, it floats for a short time, allowing the uterine lining to be in the optimal state for implantation, which occurs in the following week. This is crucial, as pregnancy is not officially established until the blastocyst successfully implants into the uterine wall.

Signs and Symptoms

At this stage, most women do not experience noticeable pregnancy symptoms because implantation has not yet occurred. However, some early signs may include:

• Mild cramping – A slight pulling sensation as the fertilised egg moves through the fallopian tube.
• Increased basal body temperature – If tracking body temperature, a continued rise may indicate pregnancy.

Since pregnancy hormones (hCG) are not yet at detectable levels, a pregnancy test will not show a positive result at this stage.

Week 4

At week 4, the fertilised egg completes its journey and implants into the uterine lining, marking the official start of pregnancy. This crucial step triggers the release of pregnancy hormones, which help maintain the uterine environment and support early development. 

Key Developments This Week

Implantation and Hormonal Changes

At week 4, the fertilised egg completes its journey and implants into the uterine lining. This process triggers the release of human chorionic gonadotropin (hCG), the hormone that supports early pregnancy and is detected in pregnancy tests. hCG helps maintain the uterine lining and signals the body to continue producing progesterone, which is essential for sustaining the pregnancy.

Embryo and Placenta Formation

As implantation occurs, the inner cells of the blastocyst start developing into the embryo, while the outer layer begins forming the placenta. The placenta will later take over hormone production and provide oxygen and nutrients to the baby. At this stage, tiny blood vessels are also developing, establishing a connection between the embryo and the mother’s blood supply.

Signs and Symptoms

Some women may begin to notice early pregnancy symptoms due to rising hormone levels. These can include:

• Implantation bleeding – Light spotting as the embryo attaches to the uterine wall.
• Mild cramping – A pulling or stretching sensation in the lower abdomen.
• Fatigue – Increased progesterone levels may cause tiredness.
• Breast tenderness – Hormonal changes can make breasts feel sore or sensitive.
• Heightened sense of smell – Some women notice increased sensitivity to certain odours.

Week 5

At 5 weeks pregnant, it becomes more real as changes in the body start to feel more noticeable. 

Key Developments This Week

Rapid Embryonic Growth

The embryo is growing quickly, and essential structures start taking shape. The neural tube, which will develop into the brain and spinal cord, begins to close. The heart, still in its early stages, starts beating, though it is not fully developed yet. Other organs, including the liver and kidneys, are also beginning to form. At this stage, the embryo measures about 1–2 mm long.

Hormonal Shifts and Early Pregnancy Changes

hCG levels continue rising, supporting the production of progesterone and oestrogen, which help maintain the pregnancy. These hormonal changes contribute to the development of the placenta and amniotic sac. They also lead to noticeable early pregnancy symptoms as the body adjusts to its new state.

Signs and Symptoms

• Missed period – One of the most common indicators of pregnancy.
  
  
• Morning sickness – Nausea, with or without vomiting, often triggered by certain smells.
• Fatigue – Rising progesterone levels may cause excessive tiredness.
• Frequent urination – Increased blood flow to the kidneys leads to more frequent trips to the bathroom.
• Breast tenderness – Breasts may feel sore, swollen, or more sensitive than usual.
• Mood swings – Hormonal fluctuations can affect emotions, leading to sudden mood changes.

Do’s and Don’ts for the First 5 Weeks

Do’s

• Take prenatal vitamins – Folic acid is essential for the baby’s early development and helps prevent neural tube defects.
• Eat a balanced diet – Weakness in the first trimester is due to rising Beta HCG hormone. To overcome this weakness, women are advised to have more liquids with sugar, salt and electrolytes. Excessive eating will cause weight gain which can be undesirable. Embryo needs hormonal support to grow. 
• Stay hydrated – Drinking enough water can help with digestion and prevent dehydration, which is common in early pregnancy.
• Get plenty of rest – Fatigue is common in the first few weeks, so allowing the body to recover is important.
• Engage in gentle exercise – Light activities like walking or prenatal yoga may improve circulation and ease discomfort.
• Book a prenatal appointment – Early medical guidance can provide reassurance and ensure the pregnancy is progressing well.
• Manage stress – Practicing relaxation techniques like deep breathing or meditation can help maintain emotional well-being.

Don’ts

• Avoid smoking, alcohol, and drugs – These substances can affect the baby’s development and increase the risk of complications.
• Limit caffeine intake – Too much caffeine may be linked to pregnancy complications, so it’s best to keep it in moderation.
• Do not take medication without medical advice – Certain over-the-counter and prescription drugs may not be safe during pregnancy.
• Stay away from high-risk foods – Raw or undercooked meats, high-mercury fish, and unpasteurised dairy can increase the risk of infections. Avoid raw papaya and raw pineapple all throughout the pregnancy as it can increase the risk of bleeding during pregnancy and cause premature uterine contractions and threaten an abortion. 
• Avoid strenuous activities – Heavy lifting and intense workouts may put unnecessary strain on the body.
• Do not ignore unusual symptoms – Severe cramping, heavy bleeding, or dizziness should be checked by a doctor as soon as possible.

Consult Today

As these first five weeks unfold, the changes within may be subtle, but their significance is profound. For those navigating this journey, having the right guidance can make all the difference. At Max Hospital, our obstetricians and fetal medicine specialists are here to provide clarity and care at every step—whether it’s confirming a pregnancy, addressing concerns, or planning for the weeks ahead. If you’ve recognised early signs or simply want to understand more, consider reaching out to schedule a consultation.

Frequently Asked Questions

Is light spotting normal in early pregnancy?

Light spotting can be normal in the early weeks of pregnancy and is often due to implantation bleeding, which occurs when the fertilised egg attaches to the uterine lining. This usually happens around weeks 3 or 4 and is lighter than a regular period. However, if the spotting is heavy, persistent, or accompanied by severe cramps, medical attention is recommended.

How soon can an ultrasound detect pregnancy?

A transvaginal ultrasound can typically detect a pregnancy as early as 5 to 6 weeks from the last menstrual period. Around this time, a gestational sac may be visible, and by the end of the 6th week, a heartbeat can sometimes be detected. However, the exact timing may vary based on factors such as ovulation and implantation.

Can early pregnancy cause mood swings?

Yes, hormonal changes in early pregnancy can lead to mood swings. Rising levels of progesterone and oestrogen can affect emotions, making some individuals feel more emotional, irritable, or anxious. Fatigue and physical discomfort in the early weeks can also contribute to changes in mood.

What foods can help with fatigue?

Eating nutrient-rich foods can help manage early pregnancy fatigue. Iron-rich foods like spinach, lentils, and lean meats support energy levels, while complex carbohydrates such as whole grains and oats provide sustained energy. Protein sources like eggs, nuts, and dairy can also help reduce tiredness. Staying hydrated and eating small, balanced meals throughout the day can prevent energy dips.

How much weight gain is expected up till 5 weeks of pregnancy?

Significant weight gain is not expected in the first five weeks of pregnancy. Some may gain about 0.5 to 2 kilograms, while others may not notice any changes. In some cases, nausea or food aversions may even lead to slight weight loss. A balanced diet and regular prenatal care can help maintain healthy weight gain throughout pregnancy.