What to Expect When You’re Expecting

During pregnancy your body goes through enormous changes over a relatively short space of time. Dr Lousie Howarth and Professor James Walker reveal what’s going on.

During pregnancy, the mother’s body changes to nurture her developing baby, preparing for the delivery and subsequent breastfeeding. Some of these changes make you feel great, some make you feel wretched. It’s important to remember that the mother is breathing, eating and passing urine from the baby as well as allowing it to grow inside her. The fact that most of these changes are driven by the needs of pregnancy means that most will reverse after delivery when the need is no longer there. 

The new pregnancy

Within days of fertilisation, the placenta starts to take over the mother’s body, producing pregnancy hormones that signal to the mother that she is pregnant, stop the menstrual cycle and cause the first missed period. It is these hormones that make the pregnancy test positive. Unfortunately, they also often produce nausea or morning sickness. These hormones, that maintain and support the pregnancy, cause the mother to retain more fluid and remodel her body to accommodate the baby, including the enlarging of her breasts to prepare them for milk production.

Body System Changes

The heart has to work harder by increasing the volume of each ‘pump’ and heart rate. Sometimes the mother is aware of these changes by noticing palpitations (a sensation of feeling the heart beating). Also, the blood vessels dilate, increasing blood flow to the skin and leading to a feeling of warmth and the subsequent ‘glow of pregnancy’. The widening of the vessels also causes a reduction in blood pressure, which can make pregnant women feel dizzy and faint, especially when they stand up. There is a similar rise in the blood flow through the lungs, which helps to take in more oxygen and get rid of CO2. This is helped by a faster breathing rate similar to after exercise. These changes lead to a rise in cardiovascular fitness after pregnancy and many athletes find that their performance improves as a result. Blood flow to the kidneys increases, leading to a higher excretion of nitrogen waste. This increases the urine flow, which, along with the physical pressure from the growing uterus leads to pregnant women needing to pass urine more often. Hormones relax the bowel, increasing absorption, which causes constipation. 

See also: Preparing for Pregnancy 

Size and weight

The most obvious physical change in pregnancy is a weight gain of around 12kg. This may appear a lot considering the average baby only weighs around 3.0-4.0kg. Another 2.5kg is taken up by the growth of the uterus and placenta and production of amniotic fluid around the baby. The increase in plasma volume, red cells and extra body fluid adds another 3kg. There is between 3-3.5kg of increased maternal fat, mainly on the hips and thighs, and the breasts, which on average increased by two cup sizes as they change the structure to produce milk. This weight gain is largely in preparation for breastfeeding and, since breastfeeding burns an extra 600 to 800 calories per day, this weight can often be lost after delivery. The pregnancy hormones soften the body tissues. Stretch marks may appear as a side effect of softening of skin tissue and the rapid weight gain. The growing uterus is accommodated in the pelvis until after twelve weeks so a woman may not appear pregnant until 14-16 weeks. As it grows, the uterus compresses the structures around it. The bladder is compressed both early and late in pregnancy leading to increased frequency of needing to pass urine. The veins and lymphatic drainage from the legs are compressed leading to swelling of the legs and feet and, sometimes, varicose veins, particularly in the left leg. Some women find their shoe size increases. Elevating the legs as much as possible and exercise such as walking and swimming will help reduce this. Due to the weight of the enlarging uterus, the pelvis tilts and the back arches which causes a change in gait. This, along with ligament softening, can lead to back pain and other joint problems.

Post Pregnancy

After birth, the body largely restores itself to its previous state but these changes take a varied amount of time and depend on whether the mother breastfeeds or not. Swelling may increase after delivery but a large volume of urine is passed to get rid of this within the first week. The uterus gradually returns to normal size over the first month although the abdominal muscles may still remain lax. The extra fat deposited diminishes with breastfeeding over some months. The cardiovascular adaptations may not fully revert back to normal but these are usually positive changes, and make the mother fitter in order to cope with the demanding job of motherhood. 


See also: Considering Private Midwifery 

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