Prenatal Screening & fetal abnormalities Flashcards
1
Q
What is screening?
A
- screening identifies apparently healthy people who may be at increased risk of a disease or condition, enabling earlier treatment or informed decisions
2
Q
What are the main screening tests?
A
- Early pregnancy scan
- Screening for Down’s Edward’s Patau’s syndrome
- first trimester combined test
- second trimester quad test
- 18+0 - 20+6 fetal anomaly scan
3
Q
What is the purpose of the early pregnancy scan?
A
- checks for viability
- 2-3% of women attending for the scan will have miscarried
- Accurate dating
- NICE guidance: advise using a scan of dates in lieu of LMP dates
- crucial dor screening tests for trisomies
- reduces the need for postdates induction of labour
- Detect multiple pregnancies
- determines chorionicity
- Diagnosis of major structural anomalies
- spina bifida
- anencephaly
- exomphalos & gastroschisis
- bladder outflow obstruction
- Screening for chromosomal conditions
- Down’s Syndrome - Trisomy 21
- Edward’s syndrome - Trisomy 18
- Patau’s syndrome- Trisomy 13
4
Q
What is the difference between a screening test and a diagnostic test?
A
- Screening test: identifies individuals at high or _low-_risk chance of having a baby with a conditioned screened for
- there is no risk of miscarriage in these tests
- Diagnostic test: give definitive information on the fetal chromosomes by confirming the presence of an extra chromosome or absence of one
- there is a risk of miscarriage in these tests
5
Q
Go through the pregnancy screening timeline
A
- Screening for T21, T18, T13
- combined test 11+2 to 14+1 wks
- Quadruple test 14+2 to10wks
- Screening for fetal anomaly
- anomaly scan 18-20+6wks
- Diagnostic tests
- CVS at 11+0 to 15wks
- Amniocentesis from 15 wks
- blood tests for screening should be booked by 10 wks
6
Q
What is carried out as part of the First trimester combined screening?
- what does it assess?
A
- Maternal age
- Nuchal Translucency Scan
- this is the thickness of the nuchal fluid behind the fetal neck
- the CRL (crown-rump length), can also be measured to help with dating
- Blood test for markers
- PAPP-A (pregnancy-associated plasma protein)
- low around 0.5 MoM
- Beta-hCG
- high around 2.0 MoM
- PAPP-A (pregnancy-associated plasma protein)
- this screens for chromosomal abnormalities
- has a sensitivity of 90% if the detection of T21
7
Q
What does a CRL of 45-84mm indicate?
- what is it?
A
- CRL is crown-rump length, this can be measured in a nuchal translucency (NT) scan
- and it equates to 11+2 to 14+1 weeks old fetus
8
Q
What are Maternal/ fetal influencing factors that indicate combined screening?
A
- Maternal age
- gestational age
- ethnicity
- smoking
- IVF
- Multiple pregnancies
- weight
- diabetes
- past history of chromosome abnormality
- fetal sex
- analytical imprecision
9
Q
What is carried out during the second-trimester maternal serum screening: quadruple test?
A
- only screens for T21 and is only offered to those who couldn’t do an early scan
- only blood tests are done as an NT cannot be done after 14+2 weeks
- use maternal/fetal influencing factors and maternal serum markers to give a diagnosis
- Maternal serum markers include:
lower than expected
- UE3 unconjugated estriol -the placental hormone
- AFP alpha-fetoprotein
higher than expected
- Inhibin A placental hormone
- BHCG (beta-human chorionic gonadotropin)
10
Q
What options are available if the combined or quadruple test indicates a higher chance of T13/18/21?
A
- do nothing- continue pregnancy without having further tests
- Diagnostic invasive testing (miscarriage risk)
- CVS: Chorionic Villus sampling 11+ wks
- Amniocentesis 15+ weeks to term
- Non-invasive prenatal testing (NIPT)
- available privately, planned implementation on the NHS in June 2021
- cell free fetal DNA (maternal blood from 5 weeks)
- the options should be explained to them, and a discussion about what a potential diagnosis and further testing would mean for the parent(s)
11
Q
What are the advantages of a Non-Invasive Prenatal screening Test?
A
- High detection rates, low screen positive rates
- Reduction in invasive diagnostic testing [cost effective] hence reduction in miscarriage caused by invasive testing [CVS/amniocentesis]
- A further option for women
12
Q
What are the disadvantages of a Non-Invasive Prenatal screening Test?
A
- Screening test: Not diagnostic [false positives / false negatives]
- Confirm screen positive results with an invasive test
- Not suitable for everyone, accuracy is reduced in
- multiple pregnancy
- obesity
- women at < 10wks gestation
13
Q
What is the use of ultrasound scanning reform 18+0 to 20+6 weeks?
A
- There are a main 11 conditions which are screened for at the mid-trimester scan
- the baby may benefit from treatment before or after birth
- birth is advisable in an appropriate hospital/ centre and/or to optimise treatment after the baby is born
- the baby may die shortly after birth
14
Q
What 11 conditions are screened fore at the mid-trimester scan?
A
- Ancencephaly
- Open spina bifida
- Cleft lip
- Diaphragmatic hernia
- Gastroschisis
- Exomphalos
- Serious cardiac anomalies
- Bilaterla renal agenesis
- Lathal skelatal dysplasia
- Edwards’ syndrome T18
- Pataus’s syndrome T13
15
Q
What serious cardiac anomalies are screened for at the mid-trimester scan?
A
- Transposition of the Gret arteries
- Atrioventricular Septal Defect
- Tetralogy of Fallot
- Hypoplastic Left Heart Syndrome
16
Q
Define congenital anomalies
A
- a wide range of abnormalities to body structure or function that are present at birth (during the inter-uterine development)
- they result in either physical or mental disability - often both
17
Q
M D D D
What terms are used to classify Structural Abnormalities?
A
- Malformation: flawed development of a structure or organ (eg. transposition of the great arteries)
- Disruption: alteration of an already formed organ (vascular event eg bowel atresia)
- Deformation: alteration in structure caused by extrinsic pressures (mechanical eg talipes due to reduced liquor)
- Dysplasia: abnormal organisation of cells or tissues
18
Q
Give examples of major structural congenital abnormalities
A
- Talipes equinovarus - club foot
- Neural Tube defects
- Encephalocele/ Spina bifida
- Cleft lip
- Cardiac abnormalities
- Tetralogy of Fallot
- ventriculoseptal defect
- ventricular hypoplasia
- Chromosomal defects
19
Q
What are causes of Congenital Anomalies?
A
- Genetic
- inherited/ sporadic mutation
- Ashkenazi Jews or Finns CF and Haemophilia C
- inherited/ sporadic mutation
- Infections
- Rubella, Syphilis
- Zika (potential increase in microcephaly, small not fully developed head)
- Teratogens - external factors
- alcohol, tobacco
- pesticides, medications, radiation
- Socioeconomic and demographic factors
- poorer maternal nutrition
- less screening
- maternal age
20
Q
What are some physical features of a child born with Down’s Syndrome?
A
Facial Features
- small nose and flat nasal bridge / flat face
- large tongue that may stick out of mouth
- eyes that slant upwards and outwards
- a flat back of the head / thickened skin
External features
- broad hands with short fingers
- single palmar crease
- below average wight
21
Q
What abnormalities present in T18 (Edwards syndrome)
A
- Facial abnormalities: small, abnormally shaped head, small jaw and mouth, low-set ears, cleft lip/palate
- Skeletal abnormalities: long fingers that overlap, with underdeveloped thumbs and clenched fists,
- Congenital heart defects: >90%
-
Gastrointestinal abnormalities:
- omphalocele (intestinal loop is outside the abdominal cavity), oesophageal atresia ± tracheo-oesophageal fistula,
- umbilical or inguinal hernia, pyloric stenosis
-
Urogenital abnormalities:
- Gonadal dysgenesis,
- horseshoe kidney, hydronephrosis, cystic kidneys, renal agenesis.
-
Neurological problems:
- anencephaly, hydrocephaly and other brain malformations,
- severe learning disability, seizures.
- Pulmonary hypoplasia
* infants usually die within the first year of life
22
Q
What abnormalities present in Trisomy 13 (Patau’s syndrome)?
A
- Congenital heart defects: >80%
-
Facial abnormalities: cleft lip/palate,
- abnormally small eye or eyes (microphthalmia) or absence of 1 or both eyes (anophthalmia), reduced distance between the eyes (hypotelorism), microcephaly
- Gastrointestinal abnormalities: eg, omphalocele, exomphalos
-
CNS disorder- holoprosencephaly – single brain
- varying severities of this from lobar to alobar
- Abnormally small penis in boys, enlarged clitoris in girls
- Skeletal: as extra fingers or toes (polydactyly), and a rounded bottom to the feet, known as ‘rocker-bottom’ feet
*usually die within days of birth
23
Q
What are the periods of susceptibility to teratogens in the fetuses life?
A
- 0-2 weeks: not usually sensitive during from fertilization to the formation of the embryonic disk
- 3-8 weeks: a period of greatest sensitivity
- 9-28 weeks: gradually decreasing sensitivity
24
Q
What are 8 common Teratogens?
- and what are their effects?
A
-
Warfarin
- Chondrodysplasia (dysplasia in bone development, stippling in bone x-ray at the cartilaginous ends)
- microcephaly
-
Thalidomide
- limb defects/heart defects
-
Rubella
- rubella (deafness)
-
Pesticides
- neural tube defects
-
Hyperthermia
- fetal death, neural tube defects
-
Radiation
- microcephaly, spina bifida
-
Alcohol
- Fetal Alcohol Syndrome (FAS) (maxillary hypoplasia, mental retardation)
-
Androgens
- masculinisation of external genitalia
25
What is Fetal Alcohol Syndrome and what are the defects seen in the child?
* caused by the consumption of alcohol during pregnancy
* severe maternal alcohol abuse is thought to be the biggest cause of fetal mental deficiency
* thin upper lip, short palpebral fissures,
* flat nasal bridge, short nose, elongated and poorly formed philtrum (vertical groove in the median part of the upper lip).
* thought to be more of a spectrum of presenting characteristics based o the severity of alcohol abuse
26
What congenital abnormalities can be detected via ultrasound at the following stages?
- 11+ weeks
- 20 weeks
- Third trimester
* 11+weeks – Anencephaly, Major Limb defects
* Combined screening: Nuchal translucency combined with maternal biochemistry
* 20 weeks (anomaly)
* Heart (4 chamber view), Brain/spine, Skeletal, Cleft lip and palate, Bowel, kidneys, Movements
* Third trimester
* Growth, organs as per 20/40, liquor volume, movements
27
What is the purpose of detecting these abnormalities?
* **Termination of pregnancy**
* **Treatment of the condition** :
* Treat the baby in utero: eg. cleft palate/ pulmonary shunts/tumours, transfusions, balloon occlusion of diaphragmatic hernia
* By _maternal management:_ eg. Antibiotics (eg for toxoplasmosis)
* _Plan post-delivery procedures_: CHD deliver in a tertiary centre for immediate surgery
* **Time Delivery**: diabetes
* **Allow time for acceptance/preparation by parents** – eg. Downs group/support
28
What is the process of TOP?
* Medical
* Progesterone antagonist (mifepristone) orally: stop the pregnancy
* Followed by with misoprostol (prostaglandin E1 analogue): start uterine contractions
* Dependent on pregnancy gestation, this may be done at home or in the hospital
* Surgical
* Tissue evacuated through the cervix using a suction curette
29
What are the risks of TOP?
* Mortality 0.6 deaths per 100,000 abortions (no deaths in 2014 but one in 2015 and one in 2016)
* Failure: 0.2% after surgical & 0.7% after medical
* Incomplete abortion (1%), excessive bleeding (0.1%), uterine damage (surgical) (0.5%), infection (\<1%)
