Third Month of Pregnancy: Key Milestones and Changes

Highlights

• Marks the completion of the first trimester.
• Morning sickness and fatigue remain common but may begin to subside soon.
• Emotional fluctuations are typical due to hormonal changes.
• The placenta begins to form, taking over hormone regulation.
• The fetus grows from the size of a cherry to a nectarine by the end of the month.
• First comprehensive medical check-ups and laboratory tests are conducted.
• Nutrition, oral health, and physical activity require special attention.

In This Article

• Common signs and symptoms in the third month
• Weeks included in the third month (9–13 weeks)
• Maternal body changes and possible complications
• Fetal growth and development
• Recommended medical examinations and screenings
• Nutrition and weight gain guidelines
• Sexual activity considerations
• Lifestyle advice and preventive care
• Tools and assistance for expecting parents

Overview

The third month of pregnancy marks the end of the first trimester — a critical period in fetal development and maternal adaptation. For many, this stage is challenging due to persistent nausea, fatigue, and mood swings triggered by hormonal changes. At the same time, important medical monitoring begins, setting the foundation for the months ahead.

Signs and Symptoms

The most recognizable sign at this stage is toxicosis (morning sickness), manifesting as nausea, vomiting, and heightened sensitivity to odors. Additional symptoms include:

• Slight increase in hip and waist size
• Breast enlargement and nipple darkening
• Fatigue, drowsiness, dizziness
• Digestive changes (constipation, heartburn, hemorrhoids)
• Gum bleeding due to increased demand for vitamins and minerals

Vaginal discharge may also appear. It is considered normal if it is light, odorless, and not accompanied by pain or itching. However, blood-stained or foul-smelling discharge requires medical attention, as it may indicate infection or pregnancy complications.

Weeks Included

The third month of pregnancy covers weeks 9 through 13.

• Week 9: Fetus measures 22–30 mm, weighs ~4 g (size of a cherry).
• Week 13: Fetus measures 65–78 mm, weighs 14–20 g (size of a nectarine).

Maternal Changes

• Hormonal transition: By the end of this month, the placenta takes over hormonal regulation from the corpus luteum.
• Breast changes: Increased size, heaviness, tingling, or itching; potential appearance of stretch marks.
• Circulatory system: Blood volume rises, circulation accelerates, and progesterone lowers vein tone, which may worsen varicose veins.
• Weight gain: By the end of the month, average weight gain is ~2 kg. Some individuals may lose weight due to nausea and poor appetite.
• Abdominal shape: A small fat layer forms on the belly and hips, though the pregnancy bump is usually not yet visible externally.

Fetal Development

During the third month, rapid progress occurs:

• Body proportions begin forming; head is still large compared to the body.
• Organs such as the pancreas and endocrine glands start functioning.
• Hormones and insulin production begin.
• The iris of the eye forms; lymphatic vessels develop.
• In males, testes begin forming and secreting testosterone.
• External genitalia remain difficult to distinguish, but by the end of the month, sex determination by ultrasound may be possible.

Medical Examinations

The third month is considered the optimal time for initial registration in prenatal care. Key assessments include:

• Blood and urine analysis
• HIV and sexually transmitted infection screening
• Biochemical tests
• ECG
• Vaginal and cervical examination
• Uterus size evaluation

At the end of the third month (or early in the fourth), the first ultrasound is typically performed. It helps to:

• Confirm gestational age and due date
• Evaluate fetal development consistency
• Detect potential genetic abnormalities (e.g., Down syndrome)
• Identify multiple pregnancy

Additional consultations may be scheduled with specialists (therapist, ENT, ophthalmologist, dentist, endocrinologist).

Nutrition

Balanced diet remains crucial:

• Dairy products, lean meat, fish, eggs, whole grains
• Fresh fruits and vegetables (at least 4 times daily)
• Nuts for additional vitamins and minerals
• Frequent small meals (5–7 times daily)

Fiber helps regulate digestion and prevent constipation. Excessive weight gain and unhealthy foods should be avoided.

Sexual Activity

In the absence of medical contraindications, sexual activity is not restricted during the third month. Many report heightened desire due to hormonal changes. Emotional connection, comfort, and safety remain key. Concerns or discomfort should be discussed with a healthcare provider.

Lifestyle Recommendations

• Spend at least one hour outdoors daily to ensure oxygen supply.
• Engage in safe physical activities (yoga, swimming, prenatal exercises).
• Avoid heavy lifting, abdominal strain, or high-risk sports.
• Use supportive bras, maternity clothing, and compression stockings if needed.
• Prevent falls by choosing safe footwear and using non-slip surfaces.

Tools and Assistance

• Pregnancy calculators – help track week and month progression.
• Ultrasound screening – for early evaluation of development and risks.
• Prenatal care records – medical chart documenting test results and observations.
• Specialized clothing and cosmetics – maternity wear, creams for stretch mark prevention, compression stockings.
• Support communities – online and offline groups provide emotional support and shared experiences.
• Professional consultations – regular monitoring by obstetricians and related specialists.

Summary:
The third month of pregnancy finalizes the first trimester, a stage marked by hormonal changes, organ development, and the formation of the placenta. While morning sickness and fatigue may still persist, this period is crucial for establishing medical supervision, maintaining balanced nutrition, and preparing for the next phases of pregnancy.