1. ANTENATAL SCREENING TESTS AND PRENATAL DIAGNOSİS
Selçuk Özden MD, Prof

2. SCREENING TESTS DURING PREGNANCY
Goal of screening is to detect or define risk for disease in an asymptomatic low risk population.

3. SCREENING TESTS DURING PREGNANCY
An ideal perinatal genetic screening test should:
Identify common or important fetal disorders
Be cost-effective and easy to perform
Have a high detection rate and a low false-positive rate
Be reliable and reproducible
Screen for disorders for which a diagnostic test exists
Be positive early enough in gestation to permit safe and legal options for pregnancy termination if desired

4. BASIC TESTS DURING PREGNANCY
Complete blood count
Blood typing
Fasting glucose level
Antibody screening
Pap smear
Urine analysis
Urine culture
Rubella
Hepatitis B and C
HIV

5. SCREENING of FETAL ANOMALIES
Incidence of Major congenital abnormalities: 2 to 3 percent of pregnancies.
Screening tests
Diagnostic tests

6. SCREENING of FETAL ANOMALIES
Screening for neural tube defects (NTD)
Screening for aneuploidies
Screening for fetal structural anomalies

7. SCREENING FOR NTDs
Neural tube defects (NTDs) are the second most common class of birth defect after cardiac anomalies
Reported frequency : ~ 0.9 per 1000 births.

8. SCREENING FOR NTDs Maternal Serum Alpha-Fetoprotein (MSAFP) Screening
AFP is a glycoprotein synthesized by the fetal yolk sac and later by the fetal gastrointestinal tract and liver.
It is the major serum protein in the embryo and fetus and is thus analogous to albumin.
Defects in fetal integument, such as neural-tube and ventral wall defects, permit AFP to leak into the amnionic fluid, resulting in dramatically increased maternal serum AFP levels.

9. SCREENING FOR NTDs Maternal Serum Alpha-Fetoprotein (MSAFP) Screening
Screening is generally performed from 15 through 20 weeks.
AFP is measured in nanograms per milliliter and reported as multiples of the median (MoM) of the unaffected population.
Cut-off value: 2.0 or 2.5 MoM.

10. ABNORMAL MS-AFP LEVELS

11. FACTORS INFLUENCING AFP LEVELS
Maternal weight—The AFP concentration is adjusted for the maternal volume of distribution.
Gestational age—The maternal serum concentration increases by approximately 15 percent per week during the second trimester.
Race/ethnicity—African American women have at least 10-percent higher serum AFP concentrations but are at lower risk for fetal NTDs.
Diabetes—Serum levels may be 10 to 20 percent lower in women with insulin-treated diabetes.
Multifetal gestation—Higher screening threshold values are used in twin pregnancies.

12. EVALUATION of ELEVATED AFP LEVEL
Counseling ,
Diagnostic tests
Sonography
Amniocentesis

13. SONOGRAPHIC FINDINGS
99 percent of fetuses with open spina bifida had one or more of these findings
Frontal nothcing (Lemon sign)
Small biparietal diameter,
Ventriculomegaly
Obliteration of cysterna magna,
Banana sign

14. SONOGRAPHIC FINDINGS
Lemon Sıgn
Banana Sıgn
Spına Bifida
Hidrocephaly

15. SONOGRAPHIC FINDINGS
Anencephaly
Encephalocele

16. AMNIOCENTESIS
It has been replaced in most centers by targeted sonography.
If the amnionic fluid AFP level was elevated, an assay for acetylcholinesterase was performed, and if positive, was considered diagnostic of an NTD.
Acetylcholinesterase leaks directly from exposed neural tissue into the amnionic fluid.

17. ANEUPLOIDY SCREENING
All women who present for prenatal care before 20 weeks should be offered screening

18. ANEUPLOIDY SCREENING Types of screening:
Maternal age screening is a poor screening test, because approximately 70 percent of Down syndrome pregnancies are in women younger than 35 years.
First-trimester screening at 11 to 14 weeks’ gestation, using the fetal nuchal translucency measurement together with serum analytes,
The addition of other serum analytes to second-trimester screening
Combinations of first- and second-trimester
Maternal serum cell-free fetal DNA testing for trisomy 21, 18, and 13

19. ANEUPLOIDY SCREENING

20. FIRST TRIMESTER ANEUPLOIDY SCREENING
At 11 to 14 weeks’ gestation: Fetal nuchal translucency measurement together with serum analytes, has achieved Down syndrome detection
Nasal bone

21. FIRST TRIMESTER ANEUPLOIDY SCREENING
The most commonly used screening protocol combines the NT measurement with serum hCG and PAPP-A (Pregnancy Associated Protein-A).
Detection rates: 79 to 87 percent
False-positive rate: 5 percent

22. SECOND TRIMESTER ANEUPLOIDY SCREENING
Triple test:
Between weeks gestation
AFP 
hCG 
Unconjugated estriol: 
Quadri test:
AFP, hCG, estriol and 4. inhibin are measured.
Cut-off value : 1:200
Amniocentesis and cytogenetic analysis is recommended

23. CELL FREE FETAL DNA SCREENING
Using massively parallel sequencing or chromosome selective sequencing to isolate cell-free fetal DNA from maternal plasma, fetal Down syndrome and other autosomal trisomies may be detected as early as 10 weeks’ gestation.
Detection rates for trisomies 21, 18, and 13: ~ 98%
False-positive rate: % or less.

24. CELL FREE FETAL DNA SCREENING
This technology has recently become clinically available as a screening test,
It is not considered a replacement diagnostic test.
Pretest counseling is recommended.
If an abnormal result is identified, genetic counseling and invasive prenatal diagnostic testing should be offered to confirm the results.

25. CELL FREE FETAL DNA SCREENING
Test may be offered to the following groups: (ACOG 2012)
Women 35 years or older at delivery
Those with sonographic findings indicating increased risk for fetal aneuploidy
Those with a prior pregnancy complicated by trisomy 21, 18, or 13
Patient or partner carries a balanced Robertsonian translocation indicating increased risk for fetal trisomy 21 or 13
Those with an abnormal first-, second-, or combined first and second-trimester screening test result for aneuploidy.
The College does not recommend offering the test to women with low-risk pregnancies or multifetal gestations

26. SONOGRAPHIC SCREENING
Structural anomalies (Hard markers)
Aneuploidy markers (Soft markers)
Other findings

27. STRUCTURAL ANOMALIES Cardiac defects, Central nervous system,
Facial anomalies,
Cystic hygroma,
Diaphragmatic hernia
Gastrointestinal,
Genitourinary anomalies
Nonimmun hydrops
Limb anomalies

28. STRUCTURAL ANOMALIES Cardiac defects: Atrioventricular septal defect
Aneoplody risk: 58%

29. STRUCTURAL ANOMALIES Duoadenal atresia: Double-bubble Polyhidramnios
Trisomy 21 risk: 1/3

30. STRUCTURAL ANOMALIES
Cystic hygroma:
Aneuploidy risk: 60%

31. STRUCTURAL ANOMALIES
Non immun hydrops fetalis: Aneoploidy risk: 16%

32. STRUCTURAL ANOMALIES
Diaphragmatic hernia:
Aneoploidy risk: 8-34%

33. STRUCTURAL ANOMALIES
Omphalocele:
Aneoploidy risk: 30-40%

34. STRUCTURAL ANOMALIES
Gastroschisis:
Aneoploidy risk is not increased

35. CENTRAL NERVOUS SYSTEM
Ventriculomegaly (>10 mm):
İsolated hydrocephaly: 3%
Hydrocephaly+ spina bifida: 8%
Isolated spina bifida: %
Dandy Walker Malformation
Aneuoploidy risk ↑
Holoprosencephaly
Risk of trisomy 13: %

36. FACIAL ANOMALIES Holoprosencephaly Cleft lip and palate:
Aneuploidy ↑ (tri.13 , 18)
Medyan cleft lip and palate: 82%

37. LIMB ANOMALIES Rocker-Bottom Foot: Trisomi 13, 18 ↑ Clubfoot:
Trisomi 13 ve 18 ↑
Sandal gap:

38. LIMB ANOMALIES
Clinodactily:
Clenched hand
Polydactily:

39. SOFT MARKERS
Soft markers are normal variants rather than fetal abnormalities,
In the absence of aneuploidy they do not significantly affect prognosis.

40. SOFT MARKERS Nuchal skinfold thickening Echogenic intracardiac focus
Renal pelvis dilation
Echogenic bowel
Short femur and humerus
Nasal bone absence or hypoplasia
Single umbilical artery
Choroid plexus cyst
Clinodactily
Echogenic bowel

41. SOFT MARKERS Nuchal skinfold thickening
A measurement ≥ 6 mm is considered abnormal
Nasal bone absence
In approximately two thirds of fetuses with Down syndrome, the nasal bone is not visible at the 11- to 14-week examination

42. SOFT MARKERS Echogenic fetal bowel
it increases the risk for Down syndrome approximately sixfold
Choroid plexus cyst:
Echogenic intracardiac focus

43. SOFT MARKERS
Single umbilical artery
Renal pelvis dilation

44. PRENATAL DIAGNOSTIC TESTS
Invasive procedures used in prenatal diagnosis:
Amniocentesis,
Chorionic villus sampling, and
Fetal blood sampling
Preimplantation genetic diagnosis permits similar diagnoses to be made in oocytes or embryos before implantation.

45. AMNIOCENTESIS
Is the most common invasive procedure used to diagnose fetal aneuploidy and other genetic conditions.
It is generally performed between 15 and 20 weeks’ gestation.
The time needed for karyotyping is 7 to 10 days.

46. AMNIOCENTESIS Complications
Fetal loss rate following midtrimester amniocentesis : In sigletons: 1 per 300 to In twins: 1.8%
Amnionic fluid leakage in 1 to 2 percent and
Chorioamnionitis in less than 0.1 percent
Needle injuries to the fetus are rare.

47. EARLY AMNIOCENTESIS
If performed between 11 and 14 weeks, amniocentesis is termed “early.”
Sac puncture may be more challenging due to lack of membrane fusion to the uterine wall.
Higher rates of procedure-related complications than other fetal procedures.
ACOG recommends against the use of early amniocentesis.

48. CHORIONIC VILLUS SAMPLING (CVS)
CVS is generally performed between 10 and 13 weeks’ gestation.
The primary advantage of villus biopsy is that results are available earlier in pregnancy, allowing safer pregnancy termination, if desired.
A full karyotype is available in 7 to 10 days.

49. CHORIONIC VILLUS SAMPLING (CVS)
Complications:
Fetal loss rate is comparable to that with amniocentesis (2 percent)
Limb reduction defects and oromandibular limb hypogenesis:
When performed at ≥ 10 weeks’ gestation, the incidence of limb defects does not exceed the background rate.
Vaginal spotting is not uncommon.
Chromosomal mosaicism is identified in up to 2 percent of specimens. Amniocentesis should be offered,

50. FETAL BLOOD SAMPLING
This procedure is also called cordocentesis or percutaneous umbilical blood sampling (PUBS).
Fetal blood karyotyping can be accomplished within 24 to 48 hours.
Fetal loss rate is approximately 1.4 percent

51. PREIMPLANTATION GENETIC TESTING
For couples undergoing in vitro fertilization (IVF), genetic testing performed on oocytes or embryos before implantation may provide valuable information regarding the chromosomal complement and single-gene disorders.
There are two separate categories of testing
Preimplantation genetic diagnosis (PGD)
Preimplantation genetic screening (PGS)

52. PREIMPLANTATION GENETIC TESTING
There are three techniques:
Polar body analysis: Sampling of first and second polar bodies should not affect fetal development
Blastomere biopsy: is done at the 6- to 8-cell (cleavage) stage when an embryo is 3 days old
Trophectoderm biopsy: involves removal of 5 to 7 cells from a 5- to 6-day blastocyst
The first and second polar bodies are normally extruded from the developing oocyte following meiosis I and II, and their sampling should not affect fetal development

53. PREIMPLANTATION GENETIC DIAGNOSIS (PGD)
When either or both members of a couple are known carriers of a specific genetic disease or a balanced chromosomal rearrangement, preimplantation genetic diagnosis (PGD) may be performed to determine if an oocyte or embryo has the defect.
Only embryos without the abnormality would be implanted.

54. PREIMPLANTATION GENETIC DIAGNOSIS (PGD)
It is used to diagnose:
single-gene disorders such as cystic fibrosis, β-thalassemia, and hemophilia;
to determine gender in X-linked diseases;
to identify mutations such as BRCA-1 that do not cause disease but confer significantly increased risk;

55. PREIMPLANTATION GENETIC SCREENING (PGS)
This term is used for aneuploidy screening that is performed on oocytes or embryos before IVF transfer. Such screening is used with couples who are not known to have or carry a genetic abnormality.
Most commonly, FISH is used to identify the copy number of selected chromosomes, and it is performed on a single blastomere

56. GESTATIONAL DİABETES SCREENING
Single step approach (75 g 2 saat OGTT)
Two-step approach
First step: 50 g 1 hours glucose screening
Second step: 100 g 3 hours Oral Glucose Tolerence Test (OGTT)

57. GESTATIONAL DİABETES SCREENING
ACOG recommend a two-step approach to screen and diagnose gestational diabetes
Screening should be performed between 24 and 28 weeks’ gestation
50-g screening test is followed by a diagnostic 100-g, 3-hour oral glucose tolerance test (OGTT)

58. GESTATIONAL DIABETES SCREENING
First step: 50-g oral glucose challenge test.
If plasma glucose level >140mg/dl
Second step: 100-g, 3-hour oral glucose tolerance test (OGTT)
Two or more of the venous plasma glucose concentrations listed must be met or exceeded for a positive diagnosis.

59. SCREENING FOR PRETERM LABOR
Measurement of cervical length by transvaginal ultrasonography: Benefit of routin screening is not clear.
Fetal fibronectin: Benefit of routin screening is not clear.
Periodontal disease: increase the risk of preterm labor independently. Treatment decrease the risk.
Bacterial vaginosis: is an independent risk factor of preterm labor.

60. SCREENING FOR PREECLAMPSIA
There is no effectiv preventive measure.
Uterine artery Doppler:
Early diastolic notch
Etkili bir önlem yok
Serum markers: are nonspecific.

61. SCREENING FOR INFECTIOUS DISEASES
Group B streptococcus screening: prevent neonatal sepsis effectively
HIV screening: ACOG recommends routin screening and treatment. Treatment decrease perinatal transmission
Rubella, Hepatitis B, varicella screening : Immunisation is offered according to immunoglobulin titer. After vaccination, contraception is recommendedfor 3 months.

62. REFERENCES
Williams Obstetrics 24.th edition-Cunningham et al. The McGraw-Hill Companies-2014
Gabbe: Obstetrics: Normal and Problem Pregnancies, 6th ed., 2013
Current Obstetrics & Gyneacology , McGrawHill, LANGE, 12 th edition 2015
Moore KL, The Developing Human, Tenth Edition, Copyright © 2016 By Elsevier, Inc.
Creasy And Resnik’s Maternal-fetal Medicine, Seventh Edition, Elsevier Saunders, 2014