Obstetrics Basics Flashcards
Describe the female HPO axis in:
1) follicular phase
2) midcycle
3) luteal phase
4) pregnancy
Describe LH, FSH, oestradiol and progesterone changes during the menstrual cycle
Describe foetal growth (correlate organs grown with gestational age)
The vast majority of all the organogenesis will be completed by week 12.
The CNS continues to develop throughout the last few stages of pregnancy, + after the birth
Why might SFH (symphysis-fundal height) be lower or higher than expected?
If we measure a baby that is smaller, it may be because
- We have the wrong dates
- The baby is small for gestational age
- Oligohydramnios
- Transverse lie
Larger: wrong dates
- We have the dates wrong
- Molar pregnancy
- Multiple gestation
- Large for gestational age
- Polyhydramnios
- Maternal obesity
- Fibroids
When is SFH measured? When is this plotted on a growth chart?
- SFH measured from 24wks –> plot on growth chart
- every antenatal visit from 24wks should measure SFH
Which biometric parameters are used to measure foetal growth on US?
- 11+3 – 13+6 wks = CRL (crown-rump length = 45-84mm)
- 14-20wks = HC (head circumference)
- 20+ wks = USS biometry (biparietal diameter, head circumference, abdo circumference and femur length serially for 4wks)
- CRL and HC alone become less accurate (genes and environmental factors influence foetal size)
What is the purpose of the anomaly scan?
- 20-22 weeks
- Detailed structural scan to assess foetal anatomy à can detect spina bifida, major congenital anomalies, diaphragmatic hernias, renal agenesis etc.
- Assesses growth and size
- Assesses amniotic fluid volume
- Placental position
What is the combined screening test that occurs at the dating US scan?
- screens for Down’s and other chromosomal abnormalities (Edward’s, Patau’s)
- 3 parts to combined screening test:
- Measurement of nuchal translucency on USS
- Measurement of beta hCG and pregnancy-associated plasma protein A (PAPP-A)
- In trisomy 21 the b-hCG conc is higher (2x) and PAPP-A is lower (0.5x)
- Maternal age
- –> These are combined to give a risk of Down’s à 90% detection rate
- 3 parts to combined screening test:
When is the quadruple test indicated? What is this?
- Screening for Down’s, Patau’s and Edward’s can also be done between 14-20wks or if nuchal translucency measurement is not possible –> uses quadruple test (only maternal biomarkers)
- Measures maternal AFP, hCG, unconjugated oestradiol and inhibin A
- 80% detection rate with 5% false positive rate
When is invasive prenatal testing indicated?
- If a high-risk result is given (for Down’s, Edward’s and Patau’s from the quadruple/combined screening test) the mother can be offered invasive prenatal testing to confirm the diagnosis (CVS/amniocentesis)
- Remember high-risk is usually 1 in 150
- If diagnosis is confirmed, mother must be counselled about continuing vs TOP
Describe the hormonal changes that take place during pregnancy
Human chorionic gonadotrophin is the key hormone produced by human pregnancy. It is a functional homologue of LH, driving the production of oestrogens and progesterones from the ovaries (drives the corpus luteum).
The corpus luteum degenerates towards the end of the last week of the menstrual cycle. The fall in progesterone results in the breakdown of endometrium. To keep the pregnancy going, we need progesterone. HcG drives the progesterone production from the corpus luteum. It peaks and falls in the first trimester.
Placental lactogen is produced, and levels increase as the size of the placenta increases. The same pattern of production is seen in progesterone and oestrogens.
There is a switch over in the production of steroids: for the first couple of months, the corpus luteum produces these hormones. For the next few months, the placenta takes over oestrogen/progesterone production.
- hCG shows peak levels in maternal plasma in the first trimester, and declines thereafter
- Other main hormones (or hormone families) increase as pregnancy progresses
- Increases in progesterone, oestrogens and placental lactogen parallel the increased size of the placenta
- By 10 weeks gestation, the placenta is the source of all progesterone (up to then, mainly corpus luteum)
Levels of progesterone (up to 1µM) and estrogens (up to 20nM) greatly exceed the levels seen during the normal menstrual cycle, so they may have potent effects on the maternal system in pregnancy. Low progesterone levels, or administration of a progesterone antagonist, will lead to loss of the pregnancy at all gestational ages.
The maternal endocrine system is modified substantially during pregnancy, with the high levels of steroids suppressing the HPG, leading to very low levels of LH and FSH throughout pregnancy, and hence no cyclic ovarian or uterine functions.
Describe the 3 phases of labour
-
PHASE I: can last many hours, and involves contractions and cervical/uterine changes
- Contractions become more powerful and more coordinated
- The cervix begins to soften (ripening) and gets thinner (effacement)
- The length of phase I is incredibly variable (12 to 48 hours)
- PHASE II: can last hours, and the baby is delivered in this phase
- PHASE III: approximately half an hour long, in which the placenta is delivered
What are the stages in Phase 1 of labour?
-
Cervical ripening and effacement
- Change from rigid to flexible structure
- Remodelling (loss) of extracellular matrix
- Recruitment of leukocytes (neutrophils)
- This is an inflammatory process – production of:
- Prostaglandin E2, interleukin-8
- Local (paracrine) change in IL-8
-
Co-ordinated myometrial contractions
- Fundal dominance
- Increased co-ordination of contractions
- Increased power of contractions
- Key mediators
- Prostaglandin F2a (E2) levels increased from fetal membranes
- Oxytocin receptor increased
- Contraction associated proteins
- Rupture of foetal membranes
- Loss of strength due to changes in amnion basement component
- This is what is happening when a woman’s ‘water breaks’
- Inflammatory changes, leukocyte recruitment
- This is modest in normal labour, exacerbated in pre-term labour
- Increased levels and activity of MMPs
- Inflammatory process in fetal membranes
Which parameters are observed and are clinically important on a CTG? (how does one read a CTG?)
DR C BRAVADO
- DR: Define risk
- C: Contractions
- BRa: Baseline rate
- V: Variability
- A: Accelerations
- D: Decelerations
- O: Overall impression
What are some reasons a pregnancy may be defined as high risk?
Maternal medical illness
- Gestational diabetes
- Hypertension
- Asthma
Obstetric complications
- Multiple gestation
- Post-date gestation
- Previous cesarean section
- Intrauterine growth restriction
- Premature rupture of membranes
- Congenital malformations
- Oxytocin induction/augmentation of labour
- Pre-eclampsia
Other risk factors
- Absence of prenatal care
- Smoking
- Drug abuse
Which parameters are used to assess (maternal) contractions?
Duration: How long do the contractions last?
Intensity: How strong are the contractions (assessed using palpation)?
What does each 1 big square in a CTG equal to time-wise?
1 big square = 1 minute
What is a normal foetal HR?
normal fetal heart rate is between 110-160 bpm
List some causes of foetal tachycardia
Causes of fetal tachycardia include:
- Fetal hypoxia
- Chorioamnionitis
- Hyperthyroidism
- Fetal or maternal anaemia
- Fetal tachyarrhythmia
In which situations is it common to have a baseline foetal heart rate of between 100-120 bpm ?
- Postdate gestation
- Occiput posterior or transverse presentations
Define Severe prolonged bradycardia. What does it indicate?
<80 bpm for more than 3 minutes, indicates severe hypoxia
What are some causes of prolonged severe foetal bradycardia?
Causes of prolonged severe bradycardia include:
- Prolonged cord compression
- Cord prolapse
- Epidural and spinal anaesthesia
- Maternal seizures
- Rapid fetal descent
What is normal variability in foetal HR?
Normal variability is between 5-25 bpm
How can foetal HR variability be categorised?
Variability can be categorised as either reassuring, non-reassuring or abnormal.
Define a reassuring foetal HR variability
Reassuring: 5 – 25 bpm
Define a non-reassuring foetal HR variability
Non-reassuring:
- less than 5 bpm for between 30-50 minutes
- more than 25 bpm for 15-25 minutes
Define an abnormal foetal HR variability
Abnormal:
- less than 5 bpm for more than 50 minutes
- more than 25 bpm for more than 25 minutes
- sinusoidal
Why might reduced foetal HR variability occur?
Reduced variability can be caused by any of the following:
- Fetal sleeping: this should last no longer than 40 minutes (this is the most common cause)
- Fetal acidosis (due to hypoxia): more likely if late decelerations are also present
- Fetal tachycardia
- Drugs: opiates, benzodiazepines, methyldopa and magnesium sulphate
- Prematurity: variability is reduced at earlier gestation (<28 weeks)
- Congenital heart abnormalities
Define accelerations in foetal HR
Accelerations are an abrupt increase in the baseline fetal heart rate of >15 bpm for >15 seconds.
Are foetal HR accelerations reassuring or non-reassuring?
accelerations = reassuring