11 - Second trimester to birth

Question 1

12 weeks

Answer 1

• 78 mm
• 26g
• epidermis
• bone, musculature
• central nervous system – brain and spinal cord
• gall bladder, pancreas
• external genitalia

Question 2

Second trimester

Answer 2

• 640g at 24 weeks
• hair and nails
• movement (felt at 18-22 weeks)
• alveoli form, nostrils open
• 5-40% chance of survival, if born at or before 24 weeks

Question 3

Respiratory distress syndrome

Answer 3

The absence of lung surfactant in premature infants (typically infants born before 28 weeks of gestation). Can be supplied extra generously.

• The main problem is that the lungs have not fully developed by 24 weeks.
• Surfactant secreting cells become active in late stages of pregnancy, so alveoli stick together & can’t inflate.
• You can inject surfactant (a detergent) into the lungs and prevent respiratory distress syndrome. This must happen quickly after birth so the brain is not starved of oxygen.

Question 4

What happens during amnion and chorion fusion?

Answer 4

Forms amniochorion due to the baby taking up a lot of space.
A mucus plug forms.

Question 5

Third trimester

Answer 5

• 3.2kg at 40 weeks
• lungs mature
• eyelids open
• pituitary gland functional
• kidneys functional
• testes descend
- fundus position changes

Question 6

How are the internal organs affected during pregnancy?

Answer 6

Pressure on the lower back and bladder, placenta weighs 1.1kg, 5 litres of amniotic fluid.
Uterus expands as the baby grows and moves, causing Brixton hicks contractions.

Question 7

What are the functions of the placenta?

Answer 7

Produces hCG until 16-20 weeks
Produces progesterone from 12 weeks
Oestrogen levels get high prior to birth
Produces prolactin and lactogen
Relaxin- changes to cervix and pubic symphysis to inhibit oxytocin.

Question 8

Maternal physiological changes

Answer 8

• increased respiratory rate, increased tidal volume
• 50% increase in blood volume (increased aldosterone)
• low O2 -> erythropoietin -> red blood cells
• 10-30% increase in nutrient requirement = hunger
• increased urine production = elimination of foetal waste

Question 9

Changes to mammary glands

Answer 9

• Hormones convert mammary glands from an inactive to a secretory state
• By 6 months, secretions are produced which are stored in the ducts.

Question 10

Uterine changes

Answer 10

• A non-pregnant biological female has a uterus the size of an orange (30-40g).
• At the end of pregnancy the uterus occupies most of the abdominal cavity (10kg).
• Increased size due to increased muscle fibres (smooth) – myometrium.
• The smooth muscle stretches during pregnancy – as the baby moves this triggers small contractions (Braxton-Hicks); this is not ‘proper labour’.

Question 11

How is labour stimulated?

Answer 11

Increase in prostaglandin, oestrogen and oxytocin.

Positive feedback reaction occurs.

Question 12

What are the 3 stages of labor?

Answer 12

1. Dilation
2. Expulsion
3. Placental

Question 13

Dilation

Answer 13

• Lasts approximately 8 hours.
• 2-6 contractions per hour, each with a 30s duration.
• The amniochorion ruptures.
• Cervical opening dilates, eventually enough to allow baby to pass through the cervix & vagina.
• Fully dilated cervix diameter is approximately 10cm.

Question 14

Expulsion

Answer 14

• Lasts approximately 2 hours.
• Contractions every 2-3 min, with a 60s duration.
• The myometrium contracts down, forcing the baby out.

Question 15

Placental

Answer 15

• Sustained contraction of myometirum (may be aided by oxytocin injection).
• This ruptures the connections between the placenta and uterus.
• This can cause quite a lot of bleeding to occur.
• However, it’s tolerated by the mother because of the increased blood volume during pregnancy.

Question 16

What are the changes in the circulatory system that occur after birth?

Answer 16

• Prior to birth, the lungs are fluid-filled and have a relatively small supply of blood.
• After birth, the baby takes its first breath and inflates and alters the pressure in the lungs.
• Foramen ovale shunt diverts blood from right atrium to left atrium, then to the left ventricle and out the aorta.
• Pulmonary trunk connects to aorta pre-birth, diverting blood away from lungs.
• After birth, the ductus arteriosus closes and the pressure in the heart alters so blood flows from the left atrium to the left ventricle and from the right atrium to the right ventricle.
• If the foramen ovale doesn’t close after birth it’s possible to hear the disruption in the blood flow (a hole in the heart) and this can be corrected by surgery.

Question 17

Pre-eclampsia

Answer 17

• Affects about 1 in 20 pregnancies
• Most common in 3rd trimester
• High blood pressure (hypertension)
– headache
• Protein in urine (proteinuria)
• Oedema
– sudden weight gain
– swollen, puffy face
– swollen ankles

Question 18

Maternal consequences of pre-eclampsia

Answer 18

• Eclampsia – fits and convulsions
• HELLP syndrome – haemolysis, elevated plasma liver enzymes, low platelet count
• Cerebral haemorrhage
• Cortical blindness
• Acute renal cortical and tubular necrosis
• Pulmonary oedema and respiratory distress syndrome
• Laryngeal oedema
• Intravascular blood clots
• Hepatic infarction
• Hepatic rupture

Question 19

Foetal consequences of pre-eclampsia

Answer 19

• placental dysfunction
– slow growth
– asphyxia
– premature labour
– intrauterine death.

Question 20

Gestational diabetes

Answer 20

• increased maternal insulin resistance
• low maternal insulin levels
• increased blood glucose
Causes the baby to make insulin so can become hypoglycaemic.

Question 21

Rhesus disease

Answer 21

• During delivery, Rh antigens enter mother’s circulation through breaks in placenta
• Mother makes anti-Rh antibodies
• In a subsequent pregnancy, these antibodies cross placenta and destroy foetal blood cells
  • May lead to anaemia and, possibly, intrauterine death.
  • Prevented by injecting at-risk mothers (Rh-) with anti-Rhesus antibodies at 28 weeks (booster at 34 weeks).