Biochemical markers of prenatal diagnosis

1. BY
Dr KHALED SALEH
30 April 2014

2. Definition:
‘Prenatal diagnosis is defined as the detection of
abnormalities in the fetus, before birth’
Screening is the process of surveying a population,
usinga specific marker or markers and defined
screening cut-off levels, to identify the individuals
in the population at higher risk for a particular
disorder.

3. The purpose of prenatal diagnosis is not simply to detect
abnormalities in fetal life and allow termination.It rather
have following goals :
Provide a range of informed choice to the couples at risk of
having a child with abnormality.
Provide reassurance & remove anxiety, especially among
high risk groups.
Allow couples at high risk to know that the presence or
absence of the disorder can be confirmed by testing.
Allow the couples the option of appropriate management
( psychological, pregnancy/delivery, postnatal)
To enable prenatal treatment of the fetus.

4. Some Disorders for which PRENATAL DIAGNOSIS is
available:
1. Congenital malformations
2. Chromosomal disorders
3. Non genetic Fetal disorders
Fetal infections, Immune hydrops, DM,Fetal effects of maternal drugs
e.g valproic acid
4. Single gene disorders
-Multiple malformation synd
*Holt oram, Craniosynostosis, Orofacial digital synd
-Hematological disorders
*Thalassemias, Hemoglobinopathies, Hemophilia
-Metabolic Disorders
*Tay sach, Wilson,
-Neuromuscular disorders
*Huntington chorea, Myotonic dystrophy, Fragile X

5. -Renal Disoders
*kidney disease
-Connective tissue dis / Skeletal dysplasia
* Osteogenesis imperfecta, Ehlers Danlos, Achondroplasia,
Marfan.
-Skin disorders
*Epidermolysis bullosa, Ectodermal dysplasia
5

6. Down’s Syndrome
 – Down’s syndrome (DS) is a congenital disorder,
caused by a trisomy of chromosome 21
 – risk increases with the mother’s age

7. Incidence of Down’s Syndrome
 Down syndrome is a chromosomal disorder caused by
an error in cell division, the likelihood of such an error
occuring increases with maternal age.
This means that an older mother is more likely to give
birth to a child with Down sydrome than her younger
counterpart.
The likelihood of a woman under 30 years of age giving
birth to a child with Down syndrome is less than
1:1000, but increases the older the woman gets (see
chart below), with an incidence of about 1:100 and 1:30
at 40 and 45 years of age respectively.

8. Risk of DS and Chromosomal Abnormalities
at Term
Maternal Age at
Delivery (yr)
Risk of DS Risk of Any
Chromosomal
Abnormality
20 1/1650 1/530
25 1/1250 1/480
30 1/950 1/390
35 1/385 1/180
40 1/100 1/65
45 1/30 1/19

9. Neural tube defects
 NTD (Neural tube defects) can affect 1 in 500 infants
 – Commonest forms of NTD known as anencephaly or
spina bifida
 – Neural tube beneath the backbone fails to develop
definitive diagnosis relies on amniocentesis
 – high levels of AFP (Alphafetoprotein) seen in NTD

10. BIOCHEMICAL MARKERS PRENATAL DIAGNOSIS
1- Alpha-fetoprotein (AFP)
a protein synthesized by the fetus is detectable in
maternal serum from week 6 of pregnancy,with a
peak in week 34 of gestation (4 mg / ml), its value
decreasing in 8-12 months after birth.
Measurement of alpha-fetoprotein can be done
from amniotic fluid or from maternal blood.

11. Elevated values of alpha-fetoprotein are found in:
 Multiple pregnancies
 Skin diseases;
 Organ failure;
 Congenital nephropathy;
 Cystic higroma;
 Hepatic necrosis;
 Neural tube defects
 Abdominal wall defects.


12. Low values of alpha-fetoprotein are recorded in cases
Chromosomal abnormalities
Defects of the placenta
Fetal hydrops
Trophoblastic disease
Diabetic mothers

13. BIOCHEMICAL MARKERS PRENATAL DIAGNOSIS
2-Human Chorionic Gonadotropin
 The hormone human chorionic gonadotropin (better
known as HCG) is produced during pregnancy. It is
made by cells that form the placenta, which nourishes
the egg after it has been fertilized and becomes
attached to the uterine wall.
 Levels can first be detected by a blood test about 11
days after conception and about 12 - 14 days after
conception by a urine test.
 In general the HCG levels will double every 72 hours.
The level will reach its peak in the first 8 – 11 weeks of
pregnancy and then will decline and level off for the
remainder of the pregnancy.

14.  There are two common types of HCG tests. A
qualitative HCG test detects if HCG is present in
the blood. A quantitative HCG test (or beta HCG)
measures the amount of HCG actually present in
the blood.

15. What can a low HCG level mean?
 A low HCG level can mean any number of things and
should be rechecked within 48-72 hours to see how
the level is changing. A low HCG level could indicate
 1- Miscalculation of pregnancy dating
 2-Possible miscarriage or blighted ovum
A blighted ovum (also known as “anembryonic pregnancy”) happens when a
fertilized egg attaches itself to the uterine wall, but the embryo does not
develop. Cells develop to form the pregnancy sac, but not the embryo itself.
A blighted ovum occurs within the first trimester, often before a woman
knows she is pregnant. A high level of chromosome abnormalities usually
causes a woman’s body to naturally miscarry.

16.  3- Ectopic pregnancy
An ectopic pregnancy occurs when
the fertilized egg attaches itself in a
place other than inside the uterus.
Almost all ectopic pregnancies
occur in a fallopian tube, and are
thus sometimes called tubal
pregnancies. The fallopian tubes
are not designed to hold a growing
embryo; the fertilized egg in a
tubal pregnancy cannot develop
normally and must be treated. An
ectopic pregnancy happens in 1 out
of 50 pregnancies

17. What can a high HCG level mean?
 A high level of HCG can also mean a number of
things and should be rechecked within 48-72
hours to evaluate changes in the level.
 Miscalculation of pregnancy dating
 Molar pregnancy
A molar pregnancy is an abnormality of the placenta,
caused by a problem when the egg and sperm join
together at fertilization. Molar pregnancies are rare,
occurring in 1 out of every 1,000 pregnancies. Molar
pregnancies are also called gestational trophoblastic

18. Can anything interfere with my
HCG levels?
 Nothing should interfere with an HCG level except
medications that contain HCG. These medications
are often used in fertility treatments.
 All other medications such as antibiotics, pain
relievers, contraception or other hormone
medications should not have any effect on a test
that measures HCG.

19. BIOCHEMICAL MARKERS PRENATAL DIAGNOSI
3-Beta-human chorionic gonadotropin(β- HCG)
3 weeks LMP: 5 – 50 mIU/ml
4 weeks LMP: 5 – 426 mIU/ml
5 weeks LMP: 18 – 7,340 mIU/ml
6 weeks LMP: 1,080 – 56,500 mIU/ml
7 – 8 weeks LMP: 7, 650 – 229,000 mIU/ml
9 – 12 weeks LMP: 25,700 – 288,000 mIU/ml
13 – 16 weeks LMP: 13,300 – 254,000 mIU/ml
17 – 24 weeks LMP: 4,060 – 165,400 mIU/ml
25 – 40 weeks LMP: 3,640 – 117,000 mIU/ml
Non-pregnant females: <5.0 mIU/ml
Guideline to HCG levels during pregnancy/
LMP Last menstrual period

21. BIOCHEMICAL MARKERS IN PRENATAL DIAGNOSIS
4-Unconjugated estriol
 Estriol (E3) is one of the three major naturally occurring
estrogens, the others being estradiol (E2) and estrone (E1).
 In non-pregnant females, the major estrogen is estradiol
produced by the ovaries.
 During pregnancy, estriol is secreted by the placenta and fetus
and becomes the dominant estrogen form.
 The primary form of estriol measured during pregnancy is
unconjugated estriol (also referred to as “free” estriol or uE3).
 Maternal serum uE3 levels have been used as a functional
marker of the fetal-placental unit and in the evaluation of
pregnancy complications.

22. BIOCHEMICAL MARKERS OF PRENATAL DIAGNOSIS
5- Inhibin - A
 Inhibins are glycoprotein hormones of which there are two
molecular forms, inhibin A and inhibin B.
 Classically, inhibin is known to have a negative feedback
effect on pituitary follicle-stimulating hormone secretion.
 Inhibin A is the predominant molecular form of inhibin in
maternal circulation from 4 weeks of gestation.
 The precise biological function of inhibin A in pregnancy is
could be a better marker of placental function than human
chorionic gonadotropin because of its shorter half-life.
 The possible clinical applications for the measurement of
inhibin A in early pregnancy could be in predicting
miscarriage, Down's syndrome, preeclampsia, and fetal
growth restriction in the first and/or second trimester
before the onset of the clinical symptoms.

23. BIOCHEMICAL MARKERS OF PRENATAL DIAGNOSIS
6- Pregnancy-associated plasma protein-A
 It largest of the pregnancy associated proteins produced
by both the embryo and the placenta during pregnancy
 This protein is thought to have several different functions,
including preventing recognition of the fetus by the
maternal immune system, matrix mineralization and
angiogenesis.
 Detection of this protein is also suggested as a first and
second trimester diagnostic test for aneuploidies,
including Trisomies 21 or Down’s Syndrome

24. Prenatal Screening Modalities for DS and
trisomy 18
 Integrated Prenatal Screening (IPS)
 Serum Integrated Prenatal Screening (Serum IPS)
 First Trimester Screening (FTS)
 Quadruple maternal serum screening (Quad)
 Maternal serum screening (Triple)
What is available in your community?

25. Integrated Prenatal Screening (IPS)
 2 step screening combining:
 T1 (11-13+ 6/7 weeks – ideally 11)
 Nuchal translucency measurement
 Maternal serum marker
 PAPP-A (pregnancy-associated plasma protein)
 T2 (15-20 weeks – ideally 15-17)
 Maternal serum markers
 AFP, uE3, HCG

26. Nuchal Translucency
 Subcutaneous fluid-filled space located
between back of fetal neck and skin. At
minimum an NT scan will measure CRL to
determine gestational age (GA) and the NT
 Crown-rump length (CRL) is the
measurement of the length of human
embryos and fetus from the top of the
head (crown) to the bottom of the
buttocks (rump)
 Measured on U/S between 11–13+ 6/7
weeks, measurement is not valid outside
of this time period
 NT increases with gestational age
Age CRL
6.1Weeks 0.4 cm
7.Weeks: 1.0 cm
8.Weeks: 1.9 cm
9.Weeks: 2.5 cm
10.Weeks 4.0 cm
12.Weeks 5.5 cm
13.Weeks 6.90 cm
14.Weeks 8.0 cm

27. Nuchal Translucency
Increased NT associated with:
 Trisomies 21, 18, 13, triploidy and
Turner syndrome
 Spontaneous fetal loss
 With normal chromosomes:
cardiac defects, diaphragmatic
hernia, pulmonary defects, skeletal
dysplasias, congenital infection,
metabolic/haem disorders, rare
single gene disorders
 Normal pregnancy – chance of a
normal birth varies with size of NT
measurement
NT
measurement
Chance of
normal birth
≤ 3.4mm 95%
3.5 – 4.4mm 70-86%
4.5 – 5.4mm 50-77%
5.5 – 6.4mm 67%
≥ 6.5mm 31%

28. Nuchal Translucency (NT)

29. 29

30. 30

31. Serum Integrated Prenatal Screening (SIPS)
 Serum only - 2 step approach
 Combines first and second trimester serum
markers to produce single risk assessment
 T1
 PAPP-A: 11-13+6/7 weeks
 11 weeks is ideal
 T2
 AFP, uE3, hCG, Inhibin-A: 15–20 weeks
 15-17 weeks is ideal
 Consider when NT not available
False positive rate lower with a dating ultrasound

32. First Trimester Screening (FTS)
 NT measurement: 11 to 13+6/7 weeks
 T1 serum markers
 PAPP-A, free beta hCG: 11-13+6/7 weeks
 11 weeks ideal
 NTD screening with MS-AFP and/or
ultrasound is still recommended in T2

33. Quadruple Screening – Quad test
 Second trimester maternal serum screening
 15-20 weeks – 15-17 weeks optimal
 AFP, uE3, HCG, Inhibin-A
Maternal Serum Screening (Triple)
 Same as Quad screening but without Inhibin-A
False positive rate lower with a dating ultrasound

35. Biochemical markers in the second
trimester

36. Comparison of Prenatal Screening Tests in
Detecting Down Syndrome
Test Detection Rate
(DR)
False Positive
Rate (FPR)
IPS 85 - 90% 2 - 4%
Serum IPS 80 - 90% 2 - 7%
FTS 78 - 85% 3 - 9%
Quad 75 - 85% 5 - 10%
Triple 60 - 85% 5 - 12%
NT alone 60 - 70% 5%