antenatal screening and diagnosis Flashcards
what maternal blood screening is done
- Haemoglobinopathy: Thalassaemia, Sickle cell disease
- VDRL screening
- HIV, Hepatitis B
- Maternal Rhesus antibody
- Combined first trimester serum screening for Trisomy 21 downs, 18 edward and 13 patau
when is screening done
maternal age
- first trimester combined screening, fetal NT
If they miss this then they can only do serum
integrated screening
20 week anomaly scan - useful screening tool
how many minimal scans are provided for pregnant women
2 scans
1st - dating scan, NT
2nd - detailed anatomy scan between 18-21 weeks
other reasons for having additional scans
Response to clinical concerns /findings-small for dates, polyhydramnios, oligohydramnios, reduced Fetal movements
response to raised maternal AFP
referred because they are small 3cm above or below
Why is first timester US used
- Viability
- Accurate dating - C sections
- twin determination and chorionicity - confirm it is intrauterine
- detection of fetal abnormalities-anencephaly (absent cranial bone) large anterior abdominal wall defects (gastrachiasis) cystic hygroma
- measurement of nuchal translucency
what is nuchal translucency
yellow fluid behind neck in bw image measures the space
purpose of a detailed US scan 18-21 weeks
Viability Measurements (growth) Liquor volume - around baby Fetal anatomy Placental location Assessment of normal variants for aneuploidy and fetal growth
normal variant screening in pregnancy (soft markers)
- nuchal fold >6 mm
- Ventriculomegaly>10mm
- Echogenic bowel
- Renal pelvic dilatation
- Biometry <5th centile on national charts
what should not be reported from a detailed scan
Two vessel cord
Enlarged cisterna magna
choroid plexus cysts
echogenic focus in heart
name invasive procedures done in pregnant women
Amniocentesis
Chorion villus sampling
Fetocide
Aspiration of fluid filled fetal cavities
Amnioreduction/amniodrainage
indications for amniocentesis/chorion villous sampling
1) Assessment of fetal karyotype- fetal chromosomes
maternal age, high risk for aneuploidy screening, abnormal ultrasound findings, parental translocation, maternal request
2) Molecular genetic testing –
autosomal recessive/ dominant conditions
3) Virology screen
To assess for fetal infections eg CMV
what is amniocentesis
getting fluid from around the baby
Ideally after 15 weeks of gestation - if done earlier miscarriage rate may increase
Should be performed under direct Ultrasound guidance
15-20 ml aspirated using 22 G needle
Culture of amniocytes, harvesting and banding; Microarrays, Rapid testing ( FISH/PCR)
risks of amniocentesis
Risk of miscarriage 0.5-1%
preterm delivery
chronic liquor leak
what is chorion villous sampling
- Ideally after 10 weeks
- sample from placental tissue
- Ultrasound guided with continuous visualisation of needle tip
- Transabdominal/transcervical
Sample to cytogenetic/molecular genetics
risks of chorion villous sampling
Risk of miscarriage 1%
Risk of culture failure 1%
mosaicism 1%
what is fetocide
done by fetal medicine specialists
Detection of serious fetal abnormality and aneuploidy often delayed until the anomaly scan 20-22 weeks’ gestation
Distressing for parents to faced with the delivery of their baby with signs of life
Induction of labour with prostaglandins preceded by fetocide after 22 weeks of gestation in many countries.
lidocaine
recent advances to get chromosomal problems
Use of molecular cytogenetics-FISH ( Fluorescence in situ hybridisation) visualisation of specific DNA sequences
Use of PCR-for aneuploidy, infections
indications for preimplant genetic diagnosis
Known balanced parental translocation
Increased maternal age
Familial history of X-linked recessive disorders
advantages of non invasive prenatal diagnosis
Less invasive diagnostic techniques that probe the fetal genome through either isolation and
characterisation of DNA from fetal cells identified in the maternal circulation or analysis of free fetal DNA in maternal plasma.
reduces risk of miscarriage
Circulating fetal nucleated red blood cells, mesenchymal stem cells, and trophoblast have all been used for various prenatal diagnostic tests.
what is free fetal DNA
progressively increases during pregnancy, has been estimated to account for approximately 3% to 6% of total DNA in maternal plasma, smaller amounts in serum.
Estimates of the number of fetal cells in the maternal circulation vary depending on the stage of gestation and the method used for analysis.
It is rapidly cleared from the maternal circulation and is undetectable within two hours of delivery.
3 areas where non invasive prenatal diagnosis has been used (NIPT)
Prediction of fetal rhesus phenotype from maternal plasma
Prediction of fetal sex from maternal plasma
Detection of fetal aneuploidy
Prenatal diagnosis in pregnancy
Determination of chorionicityfetal gender, number of placentas and characteristics of the membrane between the two amniotic sacs
Nuchal translucency measurement
Fetal abnormality
how is chorionicity is determined
number of placentas and characteristics of the membrane between the two amniotic sacs
characteristic sign of dichrorionic damniottic twins
lambda sign at 10-14 weeks of gestation
