Obstetric Terms

This section covers obstetric terms, procedures, acronyms, and conditions which are too small to have their own page, but are of relevance to the practice of obstetric anaesthesia and critical care.

Abortion - AB

Usually understood by patients to refer to an elective termination of pregnancy. Non-elective abortions are covered under miscarriage

Anteflexed - AF

See anteverted.

Amniotic Fluid Index - AFI

Estimate of uterine amniotic fluid volume:

Alpha-foetal protein - AFP

Maternal blood test used to evaluate for presence of foetal birth defects. AFP is:

  • Produced in foetal liver
  • Elevated in:
    • Neural tube defects
    • Abdominal wall defects
    • Abnormal placentation

Advanced Maternal Age - AMA

Pregnancy in woman over 35. Associated with ↑ risk of obstetric complications, including:

  • Placental abruption
  • Placenta praevia
  • Malposition
  • Low Birth Weight
  • Preterm Delivery
  • Post-dates delivery
  • PPH
  • Requirement for IVF
    • Subsequent ↑ risk of multiple pregnancy (due to IVF) amplifies some of the above risks

Artificial Rupture of Membranes - AROM

Deliberate breaking of amniotic membranes surrounding foetus. AROM:

  • Also known as amniotomy
  • Indications include:
    • Induce or augment labour
      With or without oxytocin infusion.
    • Perform foetal measurements
      • Apply foetal scalp electrode
      • Measure foetal lactate/pH
    • Assess composition of liquor in presence of abnormal FHR
  • Benefits:
    • Reduced length of labour
    • Reduced oxytocin requirement
      For augmented labour.
    • Allow liquor assessment
  • Complications:
    • Cord prolapse
    • Rupture of vasa praevia
    • Infection
      Proportional to number of subsequent VE’s.
    • Pain

Anteverted - AV

Normal anterior flexion of uterus over bladder.

Biparietal Diameter - BPD

Ultrasonographic measurement of foetal head width, used to produce an estimate of foetal weight and subsequently gestational age.

Bilateral Salpingo-oophorectomy - BSO

Removal of both ovaries and fallopian tubes.

Biophysical Profile - BPP

Prenatal ultrasound evaluation of foetal well-being. Evaluates:

  • FHR
  • Foetal Breathing
  • Foetal Movement
  • Foetal Tone
  • AFI

Beat-to-beat varibility - BTBV

Short-term variability in foetal heart rate.

Bilateral Tubal Ligation - BTL (“Beetle”)

Permanent technique for female sterilisation.

Breech Presentation

Where the presenting part is the bottom or feet. Breech presentations are:

  • Sometimes able to be converted to a cephalic presentation with ECV
  • Safest delivered via caesarian section
  • Subdivided into:
    • Frank (extended) breech
      Feet are next to ears with hips flexed and knees extended.
    • Complete (flexed) breech
      Foetus is cross-legged.
    • Footling breech
      One or both feet are the presenting part.

Cephalopelvic Disproportion - CPD

Mismatch between size of foetal head and maternal pelvis. Results in obstructed labour due to mechanical failure to progress, and commonly leads to caesarian section.

Cord Prolapse

Prolapse of umbilical cord through an open cervix in advance of the presenting part. Cord prolapse:

  • May lead to rapid foetal ischaemia and death - this is an obstetric emergency Requires rapid intervention and commonly operative delivery. Broadly, management consists of:
    • Minimising cord impingement
      • Replacing cord into vagina
      • Elevating the presenting part
      • Tocolysis
    • Assisted vaginal birth may be considered if cervix is dilated and presenting part is engaged
    • Emergency caesarian section is required if foetus is viable and unable to deliver vaginally.
  • Occurs in 0.2-0.4% of births
    About half are iatrogenic, due to:
    • AROM
    • ECV
    • Insertion of intrauterine pressure monitor
  • Risk factors include:
    • Malpresentation
    • LBW
    • Multiple pregnancy
    • Multiparity
    • Polyhydramnios
    • Prematurity
    • Pelvic tumours
    • Abnormally long umbilical cord
  • Differs from:
    • Umbilical cord presentation
      Umbilical cord lies in front of the presenting part, but the membranes are intact.
    • Occult umbilical cord prolapse
      Cord lies trapped beside the presenting part.

Cartiotocograph - CTG

Electronic measurement of foetal heart rate and uterine tone.

Contractions

Tightening and shorterning of uterine muscle, causing the cervix to shorten and foetus to move into the birth canal. Key terms:

  • Number of contractions
    Quantified as number per 10 minutes, e.g. 4:10.
    • Tachysystole is >5:10
      May be associated with ↑ foetal acidosis, and is associated with placental abruption.
  • Duration
    Time in seconds from onset to offset.
  • Relaxation time
    Time in minutes and seconds between contractions.
  • Resting tone
    Intrauterine pressure during relaxation.
    • Qualified as ‘soft’ or ‘firm’
    • Quantified in mmHg if transduced directly
  • Strength/intensity
    Intrauterine pressure during contaction.
    • Qualified as ‘mild’, ‘moderate’, or ‘strong’
    • Quantified as peak pressure in mmHg if transduced directly

Dilation

First stage of labour is defined by extent (in cm) of cervical dilation, and is divided into:

  • Latent phase
    Softening and shortening of cervix. Occurs from 0-3cm.
  • Active phase
    Active labour from 3-10cm. Contractions become more active and dilation continues at 0.5-1cm/hr.

External Cephalic Version - ECV

External rotation of foetus in the womb to a cephalic presentation. ECG is:

  • Associated with risks of:
    • ROM
    • APH
    • Failure
  • Contraindicated when:
    • Caesarian section required for other reasons
    • APH occurred in last 7/7
    • CTG is abnormal
    • Major uterine abnormality
    • ROM
    • Multiple presentation

External Foetal Monitoring - EFM

*See [CTG].

Estimated Gestational Age - EGA

Measure of age of pregnancy in weeks, i.e. x/40. May be calculated from:

  • Days since last menstrual period
  • Size of foetus on early obstetric ultrasound
  • Days since oocyte retrieval (if IVF)

Foetal Death in Utero - FDIU

Death occurring after point of viability, usually 20 weeks.

Group B Strep - GBS

Bacteria which commonly colonises maternal vagina. GBS colonisation:

  • ↑ risk of:
    • Preterm labour
    • PROM
    • Chorioamnionitis
    • Neonatal infection
      5% mortality from:
      • Pneumonia
      • Sepsis
      • Meningitis
  • Identified with routine antenatal culture
  • Treated with IV antibiotics during labour

Gestational diabetes - GDM

Diabetes that occurs during pregnancy. GDM:

  • Occurs in ~10% of Australian Pregnancies
  • Usually resolves following the pregnancy
  • ↑ risks of:
    • Pre-eclapsia
    • HTN
    • Premature labour
    • Macrosomia
    • IUGR
    • Caesarian section
  • Treatment includes:
    • Insulin
      First line treatment as it does not cross the placenta.

Gravida and Parity

Summary of obstetric history:

  • Gravida
    Number of pregnancies. NB:
    • Includes curent pregnancy
    • A twin pregnancy counts as 1
  • Parity
    Pregnancy carried to >20 weeks.

Related terms:

  • Nulligravida
    Woman who has never been pregnant.
  • Primigravida
    Woman with her first pregnancy.
  • Multigravida
    Woman who has had multiple pregnancies.
  • Nulliparous
    Woman who has never delivered.
  • Primiparous
    Woman who has delivered once.
  • Multiparous
    Woman who has had multiple deliveries.
  • Grand multipara
    Woman who has had 5 or more deliveries.

Hydrops Foetalis

Abnormal accumulation of fluid:

  • With at least two of:
    • Subcutaneous oedema
    • Ascites
    • Pleural effusion
    • Pericardial effusion
  • Classified into:
    • Immune
      10-20% of cases.
    • Non-immune:
      • Cardiac failure
      • Venous obstruction
      • Lymphatic obstruction
      • ↓ oncotic pressure

Intrauterine Foetal Demise - IUFD

*See FDIU.

Intrauterine Growth Restriction - IUGR

Estimated foetal weight that is under the 10th centile on ultrasound:

  • Does not imply pathology
    May be normal, but also associated with:
    • Uteroplacental insufficiency
      In turn associated with severe pre-eclampsia, which requires monitoring.
    • Antepartum stillbirth
    • Preterm delivery
  • Generally requires ↑ surveillance
  • May require early delivery for foetal or maternal reasons

Internal Foetal Monitoring

Describes foetal scalp pH and lactate electrodes, providing indications of foetal ischaemia and influence obstetric decision making around urgency of caesarian section.

Low Birth Weight - LBW

Defined as birth weight < 2500g. Related terms include:

  • Very low birth weight (VLBW)
    Weight < 1500g.
  • Extremely low birth weight (ELBW)
    Weight < 1000g.

Kleihauer-Betke Test

Quantitative assessment of volume of foetomaternal haemorrhage, used both to diagnose the presence of foetal-maternal blood transfer and determine the dose of anti-D required in an Rh- mother. The Kleihauer test:

  • Measures foetal hameoglobin
  • Has poor sensitivity and reproducibility
  • Tends to overestimate haemorrhage
  • Cannot identify the source foetal haemoglobin Most inaccurate during 2nd trimester when maternal HbF is high

Last Menstrual Perioid - LMP

Time of last menstrual period, used as a surrogate marker for when conception occured; usually 14 days after LMP.

Miscarriage

Collection of terms, including:

  • Complete miscarriage
    Return to normal uterine size following passage of all products of conception.
  • Inevitable Miscarriage
    Heavy vaginal bleeding with an open cervix and passage of products of conception.
  • Incomplete Miscarriage
    Failure to pass all products of conception.
    • May require evacuation Usually requires GA. Blood loss may be substantial.
  • Threatened Miscarriage
    Vaginal bleeding at < 20/40, in presence of a viable foetus. Threatened miscarriage is:
    • First symptom of pregnancy in ~20%
    • Suggested by small volume blood loss, minimal pain, a closed cervix, and presence of foetal heart sounds
    • Managed with bed rest and anti-D
    • Associated with ↑ risk of complete miscarriage
  • Missed miscarriage Spontaneous abortion with the absence of vaginal bleeding, see FDIU
    • Requires evacuation of products of conception
  • Septic Miscarriage
    Infection of retained products following an incomplete miscarriage.
    • Suggested by pain, fever, discharge from an open cervix
    • Requires cultures, antibiotics, resuscitation, and D&C

Nucal Cord

Where umbilical cord wraps around the foetal neck.

Oligohydramnios

Where amniotic fluid volume is less than expected for gestational age. Oligohydramnios:

  • Occurs in ~6% of pregnancies
  • Causes include:

Pregnancy Induced Hypertension (PIH)

*See hypertension of pregnancy.

Presentations

Position that the foetus sits in the birth canal. Includes:> * Cephalic
Normal, head-first. Includes: * Occiput Anterior (OA)
Includes left occiput anterior (LOA) and right occiput anterior (ROA). * Occiput Posterior (OP)
Includes left occiput posterior (LOP) and right occiput posterior (ROP). * Occiput Transverse
Includes left occiput transverse (LOT) and right occiput transverse (ROT). * Breech * Shoulder

Polyhydramnios

Where amniotic fluid volume is greater than expected for gestational age. Polyhydramnios:

  • Occurs in ~1% of pregnancies
  • Causes include:
    • Idiopathic
      Majority.
    • Maternal
      60-65% of cases.
      • GDM
      • CHF
    • Foetal
      10-20% of cases.
      • Neural tube defects
        Majority of foetal causes.
      • Foetal macrosomia
      • Gastrointestinal obstruction
        • Upper GI atresia
        • Abdominal wall defects
      • Cervical masses
      • Thoracic masses
      • Arrhythmia
      • Twin-twin transfusion
      • Hydrops foetalis

Presenting Part

Refers to which anatomical part of the foetus is closest to the birth canal. See presentations.

Preterm Premature Rupture of Membranes - PPROM

PROM occurring prior to 37 weeks.

Premature Rupture of Membranes - PROM

Rupture of the amniotic sac prior to onset of labour. May lead to:

  • Foetal:
  • Maternal:
    • Placental abruption
      See PPH.
    • Endometritis

Preterm labour - PTL

Onset of labour prior to 37 weeks. See preterm labour.

Post-Dates{#pd} - PD

Pregnancy extending past 42 weeks.

Rhesus

Refers to maternal Rhesus status, either RH(-) or RH(+). This is important as:

  • Rh(-) mothers may develop Anti-RH(+) if the foetus is RH(+)
    Due to foetal-maternal transfer of blood.
  • May lead to haemolytic disease of the newborn
    Anaemia may be:
    • Mild
      Observation/phototherapy.
    • Moderate
      Exchange transfusion.
    • Severe
      FDIU, foetal hydrops.

Rupture of Membranes - ROM

Breakage of the amniotic sac, causing amniotic fluid (the ‘waters’) to leak out of the vagina.

Small for Gestational Age - SGA

*See IUGR.

Spontaneous Abortion (SAB)

See miscarriage.

Spontaneous Rupture of Membranes - SROM

Unassisted/normal ROM.

Station

Describes location of the presenting part of the foetus in reference to the ischial spines. Operative vaginal delivery is not recommended at negative station, i.e. when the presenting part is above the ischial spines.

Termination of Pregnancy - TOP

Use of medication or surgery to end a pregnancy.

Trial of Labour After Caesarian Section (TOLAC)

Attempting normal vaginal delivery after previous caesarian. TOLAC is associated with:

  • ↑ risk of uterine rupture
  • Re-do caesarian rate of ~50%

Vaginal Birth After Caesarian Section - VBAC

Successful vaginal delivery after previous caesarian.

Vasa Praevia

Where foetal vessels within the amniotic membrane cover or are close to the internal cervical os. May lead to foetal death due to hypovolamic shock if foetal vessels rupture when ROM occurs.

Vaginal Delivery

Birth via the vagina. Related terms include:

  • Spontaneous Vaginal Delivery (SVD)
    Labor and delivery achieved without induction, assisted, or caesarian.
  • Induced Vaginal Delivery
    Artificial induction of labor, see induction of labour.
  • Normal Vaginal Delivery (NVD) Vaginal delivery without caesarian.
  • Assited/Instrumented Vaginal Delivery (AVD)
    Vaginal delivery

Vaginal Examination - VE

Internal examination performed to assess dilation, station, and presentation.

References

  1. Bell DJ, Weerakkody Y. Amniotic Fluid Index. Radiopaedia. 2018.
  2. Lau A, Refaey M. Polyhydramnios. Radiopaedia. 2018.
  3. Khoshnaw KT, Refaey M. Oligohydramnios. Radiopaedia. 2018.
  4. Smith GC, Shah I, Crossley JA, Aitken DA, Pell JP, Nelson SM, Cameron AD, Connor MJ, Dobbie R. Pregnancy-associated plasma protein A and alpha-fetoprotein and prediction of adverse perinatal outcome. Obstet Gynecol. 2006 Jan;107(1):161-6.
  5. RCOG. Induction of Labour at Term in Older Mothers. RCOG. 2013.
  6. Stanislavsky A. Biparietal Diameter. Radiopaedia. 2016.
  7. Maharaj D. Assessing cephalopelvic disproportion: back to the basics. Obstet Gynecol Surv. 2010 Jun;65(6):387-95.
  8. King Edward Memorial Hospital. Clinical Practice Guideline: Cord Prolapse: Umbilical.. Government of Western Australia North Metropolital Health Service.
  9. RANZCOG. Management of breech presentation at term. RANZCOG. 2001.
  10. Department of Health. Pregnancy Care Guidelines; Part F: Routine Maternal Health Tests 39: Group B Streptococcus. Australian Government. 2018.
  11. Nankervis A, Price S, Conn J. Gestational diabetes mellitus: A pragmatic approach to diagnosis and management. Aust J Gen Pract. 2018 Jul;47(7):445-449.
  12. Lausman A, Kingdom J; MATERNAL FETAL MEDICINE COMMITTEE. Intrauterine growth restriction: screening, diagnosis, and management. J Obstet Gynaecol Can. 2013 Aug;35(8):741-748. doi: 10.1016/S1701-2163(15)30865-3.
  13. Perinatology. Hydrops Fetalis. Perinatology. 2015.
  14. RANZCOG. Vasa praevia. RANZCOG. 2016.
  15. Garite TJ, Simpson KR. Intrauterine resuscitation during labor. Clin Obstet Gynecol. 2011 Mar;54(1):28-39.
  16. Callum J, Barrett J. Kleihauer-Betke Test. Blood Banking and Transfusion Medicine: Basic Principles & Practice. 2nd Ed. 2007.