Oxford Handbook of Midwifery by Janet Medforth, Sue Battersby, Maggie Evans, Beverley Marsh, Angela Walker Read Free Book Online Page B

estimation of fetal age. If the results differ from the menstrual date by more than 2 weeks, the scan date should be accepted as the correct date and the EDD adjusted accordingly.

Having accurate dates allows for correct interpretation of fetal screening tests and prevents unnecessary induction of labour for post-maturity.
CHAPTER 4 Antenatal care
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Adaptation to pregnancy
Increasing amounts of circulating hormones bring about pregnancy changes throughout the body, and all body systems are affected to a greater or lesser degree. The changes allow the fetus to develop and grow, prepare the woman for labour and delivery, and prepare her body for lactation.
The reproductive system
Most of the changes take place in the uterus, which undergoes hypertrophy and hyperplasia of the myometrium. The decidua also becomes thicker and more vascular.
Progesterone causes the endocervical cells to secrete thick mucus, which forms a plug, called the operculum, in the cervical canal, protecting the pregnancy from ascending infection.
Muscles in the vagina hypertrophy and become more elastic to allow distension during the second stage of labour.
The cardiovascular system
• Due to the increasing workload the heart enlarges.
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
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The ureters relax under the influence of progesterone and become dilated. Compression of the ureters against the pelvic brim can lead to urinary stasis, bacteriuria, and infection of the urinary tract.
As the fetal head engages at the end of pregnancy the bladder may become displaced upwards.
The gastrointestinal system
Nausea is experienced by 70% of pregnant women, beginning at around 4–6 weeks and continuing until 12–14 weeks.
Most women notice increased appetite and increased thirst in pregnancy.
Reflux of acid into the oesophagus, resulting in heartburn, is common.
Transit of food through the intestines is much slower and there is increased absorption of water from the colon, leading to an increased tendency to constipation.
Skeletal changes
Pelvic ligaments relax under the influence of relaxin and oestrogen,
with the maximum effect in the last weeks of pregnancy.
This allows the pelvis to increase its capacity to accommodate the
presenting part during the latter stage of pregnancy and during labour.
The symphysis pubis widens and the sacro-coccygeal joint loosens, allowing the coccyx to be displaced.
While these changes facilitate vaginal delivery, they are likely to be the