Oxford Handbook of Midwifery (23 page)

• Cardiac output increases to accommodate the increasing circulating
  

  blood volume.
  

• Peripheral resistance is lowered, due to the relaxing effect of progesterone on the smooth muscle of the blood vessels, leading to a fall in blood pressure.
  
• To avoid aorto-caval compression, as the arterial walls are more relaxed, it is important to avoid placing the woman in an unattended supine position during the third trimester.
  
• Blood flow increases in the uterus, skin, breasts, and kidneys, and blood volume increases by 20–50%, varying according to size, parity, and whether the pregnancy is singleton or multiple.
  

  The respiratory system
  

• Oxygen consumption increases by 15–20% at term.
  
• Tidal volume increases by 40%.
  
• Residual volume decreases by 20%.
  
• Alveolar ventilation increases by 5–8L/min, four times greater than oxygen consumption, resulting in enhanced gaseous exchange.
  
• The amount of air inspired over 1min increases by 26%, resulting in hyperventilation of pregnancy, causing CO
  ₂
  to be removed from the lungs with greater efficiency.
  
• Oxygen transfer to, and CO
  ₂
  transfer from, the fetus are facilitated by changes in the maternal blood pH and partial pressure of CO
  ₂
  (
  p
  CO
  ₂
  ).
  

  The urinary system
  

• Renal blood flow increases by 70–80% by the second trimester.
  
• The glomerular filtration rate increases by 45% by 8 weeks’ gestation.
  
• Creatinine, urea, and uric acid clearance are increased.
  
• Glycosuria occurs as a result of the increased glomerular filtration rate and is not usually related to increased blood glucose.
  

ADAPTATION TO PREGNANCY

47

The gastrointestinal system

Skeletal changes

with the maximum effect in the last weeks of pregnancy.

presenting part during the latter stage of pregnancy and during labour.

Skin changes

The breasts

CHAPTER 4
Antenatal care

48

• Progesterone causes growth of the lobules and alveoli, and develops the secretory ability of these structures, ready for lactation.
  
• Prolactin stimulates the production of colostrum from the second trimester onwards, and after delivery is responsible for the initiation of milk production.
  

  The endocrine system
  

  All the endocrine organs are influenced by secretion of placental hor- mones during pregnancy.
  

• Pituitary hormones
  : prolactin, adrenocorticotropic hormone (ACTH), thyroid hormone, and melanocyte stimulating hormone (MSH) increase. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are inhibited. Oxytocin is released throughout pregnancy and increases at term, stimulating uterine contractions.
  
• Thyroid hormones
  : total thyroxine levels rise sharply from the second month of pregnancy. The basal metabolic rate is increased.
  
• Adrenal hormones
  : cortisol levels increase, leading to insulin resistance and a corresponding rise in blood glucose, particularly after meals. This
  

  makes more glucose available for the fetus.
  

• Pancreas
  : due to increasing insulin resistance, the B cells are stimulated
  

  to increase insulin production by up to four times during pregnancy. In women with borderline pancreatic function, this may result in the development of gestational diabetes, affecting 3–12% of pregnant women.
  

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  CHAPTER 4
  Antenatal care
  

  50‌‌
  

  Blood values in pregnancy
  

  Table 4.1 summarizes the main components of the blood and shows the values prior to pregnancy and the changes as a result of the maternal adaptation to pregnancy.
  

• The main feature is physiological anaemia due to increased plasma volume despite a rise in the red cell mass.
  
• Decreasing plasma protein concentrations lead to lower osmotic pressure contributing to the oedema seen in the lower limbs during pregnancy. Moderate oedema when not associated with disease is an indicator of a favourable pregnancy outcome.
  

  

  Table 4.1
  The main components of blood
  

  Component	Non-pregnant	Change in pregnancy
  Plasma volume	2600mL	3850mL at 40 weeks
  Red cell mass	1400mL	1650mL at 40 weeks
  Total blood volume	4000mL	5500mL at 40 weeks
  Haematocrit (PCV)	35%	30% at 40 weeks
  Haemoglobin	12.5–13.9g/dL	11.0–12.2g/dL at 40 weeks
  Protein	65–85g/L	55–75g/L at 20 weeks
  Albumin	35–48g/L	25–38g/L at 20 weeks
  Fibrinogen	15–36g/L	25–46g/L at 20 weeks
  Platelets	150–400 x 10 3+ /mm 3	Slight decrease
  Clotting time	12min	8min
  White cell count	9 × 10 9 /L	10–15 × 10 9 /L
  Red cell count	4.7 × 10 12 /L	3.8 × 10 12 /L at 30 weeks

  

  THE BOOKING INTERVIEW
  

  51‌‌
  

  The booking interview
  

  The booking interview is a holistic assessment of the woman’s social, health, educational, and psychological needs and identifies those needing additional care. The purpose of the interview is to obtain a history and exchange information so that future care during pregnancy and birth can be planned. Both verbal and written information is given to enable parents to make informed decisions about screening tests.
  

  The following is a guide to the information given and obtained, and the investigations that can be performed during this appointment. All the information gained and given should be carefully recorded. As the interview proceeds it will be possible to establish a rapport and judge when it is appropriate to ask some of the more sensitive questions.
  

  Social considerations