Maternal Adaptations

Plasma volume expands by 45% from the 10th week. Red cell mass (total volume of all RBCs) increases by 15%. However, if you look at the ratios, there is actually haemodilution and the mother will have physiological anaemia by 28-34 weeks. Therefore Hb, haematocrit and RBC all FALL. The circulating blood volume increases by 50% by term. The blood becomes pro-thrombotic (clotting time decreases) in order to prepare the mother for all the blood loss that occurs during child birth.

The average blood loss at birth is 250ml, it can be more with a C-section. Blood loss more than 500ml within the first 24h after birth is considered a primary post-partum haemorrhage.

You can find some more information here: https://www.rcog.org.uk/globalassets/documents/patients/patient-information-leaflets/pregnancy/pi-heavy-bleeding-after-birth-postpartum-haemorrhage.pdf.

The ureters and urethra dilate due to the increase in progesterone (smooth muscle relaxant).

There are three clinical crucial signs with pre-eclampsia: high blood pressure, proteinuria and oedema.

Being 40 years or older is also a risk factor for pre-eclampsia. See this NICE Quality Standard.

Gestational diabetes appears in roughly 4% of pregnancies. It tends to recur in future pregnancies, increases risk for Type 2 DM later in life and increases risk to baby of macrosomia.

During pregnancy, there is an increased respiratory rate, increased alveolar exchange and an increased tidal volume. There is also a slight drop in pCO2 (to approximately 32 mmHg or 4.3 kPa). All these maternal adaptations to the respiratory system lead to mild respiratory alkalosis.

Cardiac output is normally 5L, this increases to 7L during pregnancy. This is due to both an increase in heart rate (by 10-15bpm) and an increase in stroke volume.

MAP falls by about 10mmHg and rises to normal as term approaches.

During pregnancy, there is an increase in progesterone which relaxes smooth muscles. This leads to decreased vascular resistance and a decreased BP. Tidal volume, vascular resistance and plasma volume all increase during pregnancy.