Week 12: Anatomical changes during pregnancy

What changes happen during early pregnancy?

Symptoms similar to secretory phase of menstrual cycle, but no menstrual period

How do pregnancy tests work?

After 2 weeks, pregnancy can be detected by hCG secretion

• cells outside blastocyst secrete hCG

• hCG goes to ovary and maintains the corpus luteum

  • released until approx. Week 8 of pregnancy, then placenta secretes E and P

• hCG levels can indicate health of pregnancy

What are the symptoms of the first trimester?

Mainly due to increases hormones - oestrogen, progesterone, hCG

• missed period

• swollen breasts

• fatigue

• morning sickness

• increased blood flow to pelvic viscera

What causes nausea and vomiting in pregnancy?

Action of GDF15 on vomiting centres in brain

• resolves in most people by end of 1st trimester

  • some others have ‘hyperemesis gravidum’

What does foetal and uterine size look like in the first trimester?

Fundal height will be in line with pubic bone

What types of testings can be done in the first trimester (2)?

1. Blood tests - hCG, prenatal screening (sex, chromosomal abnormalities)

2. Ultrasound(s)

What happens in the second trimester (5)?

‘Fun trimester’

• usually fatigue and morning sickness disappears

• growth of foetus and uterus - particularly lower portion

• breast development

• skin changes: stretching, pigmentation

• changes in uterine ligaments (growing): round ligament and uterosacral ligament

What test(s) are conducted in the second trimester?

Ultrasound - morphology (18-20 weeks)

• placenta (location) - not bottom part of placenta grows last

• baby growth, organs

What happens in the third trimester (4)?

Rapid growth of foetus (accelerates at 20 weeks, max growth at 28 weeks)

• uterus stretches, wall thins

  • from 70g - 1.1kg

  • volume from 10mL to 5L

• breast development → increase in glandular mass and secretions

• production of colostrum

• uterus - Braxton hicks ‘practice’ contractions

What happens to the cervix during pregancy?

Shortens and cervical canal widens

• due to relaxin hormone → changes protein composition of cervix

What does relaxin do?

Relaxes smooth muscle in cervix → shortens cervix and widens cervical canal

• has additional effects on muscle and ligaments

• symphysis pubis dysfunction: pain during pregnancy

What are the 3 stages of labour?

1. Cervix dilation

2. Baby is born

3. Placenta is born

Describe the hormonal control of labour

Hormonal signals: oestrogen, progesterone, prostaglandins, oxytocin, relaxin

• PGs and oxytocin can be used to induce labour

What is oxytocin?

Oxytocin is a hormone

• naturally occurring, and/or pharmacologically administered

• released through a positive feedback loop

• leads to mother-baby bonding

What happens to the perineum during vaginal delivery?

Many nerves and muscles are vulnerable to damage

• interventions for tearing → episiotomy (cut sideways)

How is breastfeeding initiated?

Prolactin is suppressed during pregnancy (by oestrogen and progesterone)

• After birth, the delivery of the placenta causes a sudden drop in progesterone and oestrogen, removing the inhibition on prolactin.

  • removal of progesterone → delivery of placenta

  • prolactin → milk production

  • oxytocin is released in response to suckling → contraction of cells around glands to expel milk

What happens to the uterus and cervix post-partum?

• Uterine involution - but remains larger than pre-pregnancy

• Cervical opening is less rounded