More blood and plasma are needed
in the body to ensure efficient levels of nutrients and oxygen are supplied to
the foetus and mum, blood volume increases by 40-50%. During pregnancy the risk
of venous thromboembolism (VTE) is higher due to the rise of coagulation
produced by the liver. Extra blood puts more pressure on the heart, making
heart rate rise by 10-20 more beats a minute causing increased cardiac output.
Normally, the heart beating faster, and increased blood volume would result in
high blood pressure, but progesterone causes blood vessels to dilate, resulting
in lower blood pressure.
The respiratory system also
adapts to pregnancy due to intra-abdominal pressure caused by the growing
uterus. Shortness of breath is experienced in the third trimester, as the
uterus grows it pushes the diaphragm 4 centi-meters upwards compressing the
lungs. This causes the functional residual capacity to decrease; however, the
total lung capacity is unaffected. Towards the end of pregnancy, the pressure
from the uterus eases when the foetus descends into the pelvis. However, the
new location of the uterus applies extra force on the urinary bladder leading
to frequent urination.
Initiation of labour starts with
the rise of oestrogen and the secretion of oxytocin from the piturity gland. These
high levels of the two hormones cause the uterus to contract, the uterus releases
prostaglandins leading to the decrease in progesterone. Towards the end of the
third trimester the body triggers an inflammatory response using surfactant
proteins to stimulate the softening of the cervix, preparing for dilation.
Contractions start the first stage of labour, labour is separated into three stages.
The first stage begins at the start of contractions to the complete opening of
the cervix, also known as the dilation stage. Gradual, mild contractions are
the latent phase of stage 1 and will be the beginning of the cervix dilating.
Once the cervix reaches 3cm stage one moves onto the active stage where the
intensity and frequency of contraction will increase to every three to four
minutes, lasting up to 90 seconds. More vigorous contractions move the head of
the baby downwards, applying pressure against the cervix. The pressure results
in the rupture of the amniotic sac, known as ‘waters breaking’.