Anatomical and Physiological Changes During Pregnancy
Pregnancy involves remarkable physical, anatomical and physiological transformations in the body. From the moment of conception to the birth of a child, the body undergoes a series of changes to support the growth and development of the foetus.
Early Signs of Pregnancy
Before any visible signs of pregnancy appear, hormonal changes begin internally. The gestation period begins when a sperm fertilises an ovum. This triggers the production of human chorionic gonadotropin (HCG), the hormone detected in pregnancy tests. Physical symptoms often appear soon after:
- Missed periods
- Swollen or tender breasts
- Frequent urination
- Morning sickness (nausea/vomiting)
- Fatigue
Anatomy Charts to Support Learning
To complement your understanding of pregnancy and the physiological changes involved, our detailed anatomical posters and charts offer a clear, engaging way to visualise key concepts. From pregnancy and female reproductive anatomy to pelvic structure and foetal development, our educational charts are ideal for students, midwifery tutors, clinics, and healthcare settings alike.
Whether you're revising for exams, teaching others, or building patient understanding, these resources provide a visual reinforcement of complex topics.
The Uterus and Early Pregnancy Changes
The uterus, normally positioned between the bladder (anteriorly) and rectum (posteriorly), is held in place by ligaments and muscles. It comprises three layers:
- Endometrium (inner layer, where the placenta attaches ~8–9 days after fertilisation)
- Myometrium (middle muscular layer)
- Perimetrium (outer layer)
Initially, physical changes are minimal, but as pregnancy progresses, the uterus begins expanding to accommodate the developing foetus.
First Trimester (Weeks 1–12)
Baby's Development
By the end of this trimester, the baby is about the size of a grain of rice. Though still tiny, essential structures like the brain, spinal cord, and heart begin to form.
Changes in Your Body
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Abdominal changes: Some bloating may occur, but the ‘baby bump’ usually isn’t visible yet.
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Breasts: Oestrogen levels rise, leading to ductal proliferation. Breasts may feel fuller, tender, and nipples may become more prominent.
- Spotting: Light bleeding occurs in around 40% of pregnant women during early pregnancy. If accompanied by pain, consult a doctor.
Second Trimester (Weeks 13–26)
Baby's Development
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Movement: The baby begins flexing limbs and may suck their thumb.
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Hair growth: Fine hair (lanugo) forms on the baby’s body and scalp.
- Proportions: Arms and legs grow in proportion to the rest of the body.
Changes in Your Body
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Visible bump: The abdomen expands significantly as the uterus grows.
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Weight gain: Approximately 0.5kg (1lb) per week is typical from week 14 onwards.
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Umbilicus: Protrusion of the navel often becomes visible.
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Pelvis: The pelvic region widens, and surrounding ligaments begin to loosen.
- Breasts: Mammary glands continue developing due to increasing prolactin.
Third Trimester (Weeks 27–Birth)
Baby's Development
By week 36, the baby’s head usually ‘engages’ in the pelvis (known as lightening).
- Average size: 48–53cm (19–21 inches)
- Average weight: 2.7–4.1kg (6–9 pounds), though this varies
Changes in Your Body
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Braxton Hicks contractions: These false labour pains may increase in intensity.
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Pelvic and cervical changes: The cervix softens and eventually dilates to 10cm in preparation for labour.
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Mobility: Back pain, pelvic discomfort or symphysis pubic dysfunction may restrict movement.
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Stretch marks: Often appear due to rapid skin stretching.
- Haemorrhoids, fatigue, and frequent urination may intensify.
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Anatomical and Systemic Changes Throughout Pregnancy
Abdomen
The abdominal muscles stretch and strengthen to support the growing uterus and foetus. Umbilical protrusion may occur as the bump grows.
Pelvic and Perineal Region
Muscles and ligaments relax due to hormonal changes. The uterus exerts pressure on the bladder, leading to more frequent urination. Towards the end of pregnancy, the cervix begins to efface (thin) and dilate in preparation for labour.
Breasts
Development continues throughout all trimesters, with increased vascularity, darkening of the areola, and nipple sensitivity. By the third trimester, the breasts are primed for lactation.
Cardiovascular System
Cardiac output increases by up to 40%. Plasma volume rises significantly, which supports placental perfusion but can also lead to oedema.
Renal System
The kidneys filter more blood, contributing to the increased urge to urinate.
Digestive System
Slower digestion due to hormonal changes may lead to constipation, bloating, and nausea (especially in the first trimester).
Musculoskeletal and Lower Limbs
Oedema (swelling) of the legs and feet occurs in roughly half of all pregnant women, due to pressure on the inferior vena cava. Joint pain, fatigue and even numbness can occur.
Discover Antenatal Education Models
For hands-on learning, our pregnancy anatomical models and charts demonstrate real-life anatomical structure, changes in pregnancy, and stages of labour. These models are an excellent way to study reproductive anatomy in a tactile and accurate way, making them ideal for midwifery students, lecturers, and healthcare professionals offering antenatal education.
With life-sized cross-sectional views and model foetuses included in certain models, they bring clarity to topics like uterine changes, cervical dilation, and foetal positioning.
Labour and Delivery
As labour approaches, regular uterine contractions signal the onset of childbirth. The cervix dilates up to 10cm, allowing the baby to pass through the birth canal.
Preparing for Labour
- Have a hospital bag packed by week 36
- Consider your birthing plan and pain relief options
- Keep newborn essentials ready (nappies, clothes, feeding supplies)
- Communicate boundaries around visitors post-birth - bonding time is essential
The Ultimate Antenatal Support Pack
To further support expectant mothers on their journey, the Antenatal Support Pack is a valuable resource worth exploring. This medically reviewed, comprehensive pack provides practical guidance on everything from birthing plans and breastfeeding to mindfulness and hospital checklists. Designed to empower women and their families, the pack encourages self-reflection, personalised planning, and meaningful discussions with healthcare professionals throughout pregnancy.
Takeaway
Pregnancy is an incredible demonstration of the human body’s adaptability. While changes occur in virtually every system, they all work harmoniously to support the development of new life. Whether you're expecting, supporting someone who is, or studying anatomy, understanding these changes is key to appreciating just how complex - and brilliant - the process really is.
If any symptoms feel concerning at any stage, consult a healthcare provider for guidance and care.
